高能暂现源 · 每日文献综述

The cosmographic condition $j(z)=1$ provides the kinematical signature of the spatially flat $Λ$CDM model independently of any specific dark-energy or modified-gravity theory. We investigate the extent to which current observations permit departures from this condition by considering three phenomenological ``almost-$Λ$CDM'' cosmographic closures, in which the cosmic jerk differs slightly from unity through a small deformation parameter $ε$. The models are constrained using Markov Chain Monte Carlo analyses of recent DESI baryon acoustic oscillation measurements together with compressed Planck cosmic microwave background likelihoods and the Union3, Pantheon+, and DESY5 Type Ia supernova compilations. Rather than assuming a parameterized dark-energy equation of state, our cosmographic framework reconstructs the expansion history directly from observations, with the effective dark-energy equation of state emerging as a derived quantity. We find that all three closures are tightly constrained to the vicinity of the $Λ$CDM cosmographic fixed point, with Planck data driving the preferred evolution toward $j_0\simeq1$ and $w_{\rm DE,0}\simeq-1$. Despite their distinct kinematical constructions, the reconstructed dark-energy evolution consistently exhibits smooth freezing behaviour close to $w=-1$, without crossing the phantom divide. Model comparison using the Akaike and Bayesian information criteria shows that the almost-$Λ$CDM models remain statistically competitive with standard dark-energy parameterizations while requiring fewer assumptions about the functional form of $w(z)$. These results demonstrate the power of model-independent cosmography for constraining the cosmic expansion history and provide a natural framework for future studies of cosmological perturbations and structure formation.

It has been proposed that the ultra-high-energy (UHE) event $\rm KM3-230213A$ detected by KM3NeT could be explained by dark matter (DM) decay. Prima facie this seems unlikely because the arrival direction of the event is opposite to the Galactic Centre. We develop a per-event test statistic to quantitively assess this possibility and forecast the required future events to exclude the DM hypothesis in favour of an isotropic signal. For the single event observed, the DM decay hypothesis is disfavoured but not excluded ($p\text{-value}_{\rm DM}\simeq0.13$--$0.15$). We emphasise how including the time-averaged detector visibility helps discrimination despite reducing the proportion of visible sky, reducing the number of events for exclusion from $\sim33$--$43$ to $\sim22$--$27$. Moving beyond this, we perform a fully time-resolved forecast and find that the required number of events for exclusion reduces by $40\%$, $\sim14$--$16$. The time variation in the signal provides vital information allowing one to exclude or confirm the DM hypothesis with much fewer events. Our results are robust against DM decay channels and halo distributions and can readily be applied to other relics distributed similarly. Our framework allows one to turn event timing into a probe of signal geometry and is generic to any UHE equatorial neutrino telescopes.

Solar Type II radio bursts are manifestations of shocks produced by explosive and eruptive solar activities, such as solar flares and coronal mass ejections (CMEs). Metric range or coronal Type II bursts are interesting because of their association with CME-driven shocks. It is therefore important to examine the correlation between the properties of Type II bursts and the associated CMEs. This, in turn, would be useful in understanding the impact of CMEs on space weather and geomagnetic activity. We conducted a statistical study of 23 coronal Type II radio bursts in the frequency range 150-20 MHz, for the period spanning 2007-2024. We correlated the frequency bandwidth of coronal Type II bursts with the angular width of the associated CMEs. Our investigation showed an anti-correlation between the two quantities with a correlation coefficient of $\approx$ -0.62. We further deduced the height of the Type II bursts (r$_{Type II}$) at the onset time of the burst and compared them with the estimated height of the associated CMEs/shocks (r$_{CME}$). With the exception of one event, for the rest of the Type II burst events, r$_{Type II}$ was $<$ r$_{CME}$. The results suggest that the CMEs with large angular widths produce narrow-band Type II emissions, and these Type II emissions could possibly be produced in the flank region of the CME-driven shock rather than at the shock front.

We examine the Repetitive Penrose Process in the rotating Simpson-Visser spacetime, whose parameter space includes regular black holes, black-bounce geometries, and traversable wormholes. Assuming that the regularization parameter remains unchanged throughout the evolution, the analysis shows that the endpoint of the repetitive process is not always determined solely by the conventional minimum spin condition. Instead, for sufficiently large values of the regularization parameter, the evolving solution may leave the parameter domain corresponding to the original two horizon black hole branch before the dynamical spin limit is reached. Within the present framework, this provides an additional geometry-induced condition that limits the continuation of the iterative sequence. The numerical results further show that the relative importance of the dynamical and geometry-induced termination mechanisms depends sensitively on the regularization parameter. For small deformations, the evolution remains qualitatively similar to that of the Kerr spacetime. As the regularization parameter increases, however, the cumulative extracted energy, the number of admissible Penrose iterations, and the efficiency of the process are progressively reduced. We also examine how the extracted energy, the final irreducible mass, and two complementary efficiency measures vary with both the regularization parameter and the particle decay radius. Overall, the present analysis indicates that, within the RSV geometry, the underlying spacetime structure influences not only the cumulative efficiency of the repetitive Penrose process but also the parameter range over which the iterative evolution remains self-consistent. These results highlight the role that spacetime geometry can play in shaping the long-term evolution of idealized Penrose-type energy extraction processes in regular rotating black-hole spacetimes.

We investigate a modified cosmological dynamics in which the Universe is composed of baryonic matter and a complex (classical) scalar field. The phase component of this field is identified with the axion field, which accounts for the dark matter contribution, while its modulus follows a $λφ^4$-like theory, associated with a dominant constant energy density and describing the dark energy component of the Universe. When the potential term of this complex scalar field is studied near its maximum, it naturally provides an interaction term between dark matter and dark energy. The cosmological model that emerges from this physical framework leads to a modified $Λ$CDM dynamics, in which the dark matter contribution is slightly and monotonically suppressed. We then construct the effective running Hubble constant associated with this revised cosmological scenario and we compare this diagnostic tool with the binned data of the Pantheon Sample of Type Ia Supernovae. As a result of the fitting procedure, we are able to provide a satisfactory interpretation of the data in terms of our theoretical conjecture that results statistically favored with respect to the $Λ$CDM model.

The redshifted 21-cm line of neutral hydrogen (HI) is a powerful tracer of large-scale structure, and post-reionization HI intensity mapping is emerging as a competitive cosmological probe whose interpretation requires a description of how HI populates galaxies and dark matter halos. We characterize the HI--halo mass relation, its redshift evolution, and its intrinsic scatter, identifying its secondary dependences. We use the updated GAlaxy Evolution and Assembly (GAEA) semi-analytic model, applied to the Millennium-I and Millennium-II simulations, to predict the HI mass function (HIMF) and the HI--halo mass relation from the present day to redshift $z\simeq5$. At $z=0$, the model reproduces the observed HIMF and its decomposition by host-halo mass. The median HI--halo mass relation rises with halo mass, peaks near $10^{11.7}\,M_\odot$, declines as central galaxies are quenched by feedback from active galactic nuclei, and rises again where satellites dominate, approaching a single power law at high redshift. We show that the substantial scatter, of about 0.5 dex, is not random but is governed by halo assembly: at fixed mass, higher-spin, later-forming, and less-concentrated halos are systematically HI-richer, with spin together with either concentration or formation time accounting for part of this scatter and leaving an intrinsic dispersion of about 0.3 dex. We encode the median relation, these secondary trends, and the intrinsic scatter in a compact, physically motivated prescription expressed entirely in terms of quantities available in dark-matter halo catalogs. This prescription reproduces the full scatter and enables the construction of large-volume 21-cm mock catalogs for interpreting ongoing intensity-mapping measurements with SKA precursor facilities, such as MeerKAT, and for preparing for forthcoming surveys with the SKA.

The aim of this work is to investigate particle acceleration by shock waves in the magnetospheres of supermassive black holes, where the magnetic field is vortex-driven. For this purpose, we investigated the first-order Fermi acceleration process at relativistic shocks in the magnetospheres of supermassive black holes. In our analysis, we considered synchrotron radiation and inverse Compton scattering as the principal energy-loss mechanisms limiting the maximum attainable particle energy. We investigated the acceleration of both protons and electrons and demonstrated that, for a typical supermassive black hole with a mass of $10^8$ solar masses, protons can be accelerated to energies of several hundred PeV, whereas electrons can attain energies of up to approximately 120 GeV.

We investigate the effect of local cosmic voids on low-redshift measurements of the Hubble rate in flat $w_0w_a$CDM cosmologies. Using a hydrodynamical model for isolated spherical inverse top-hat underdensities, we compute the void-induced Hubble shift as a function of redshift, enclosed density contrast $δ_{\rm E}$ and cosmological parameters. We find that the effect is mainly controlled by the matter sector, through $δ_{\rm E}$ and $Ω_{\rm m,0}$, while dynamical dark energy gives only subdominant late-time corrections. For a Planck-calibrated $Λ$CDM background, matching the SH0ES value requires a present-day void with $δ_{\rm E}(z=0)\simeq -0.44$, substantially deeper than the KBC-like local underdensity. A KBC-like void lowers the SH0ES-Planck discrepancy to about $2σ$, but is not deep enough to fully reconcile the two measurements. Allowing for dynamical dark energy, including regions motivated by recent DES and DESI analyses, changes this result only at the percent level. We also show that the reported redshift dependence of locally inferred $H_0$ values can be represented phenomenologically by an effective enclosed matter profile. This reconstruction should be interpreted as a consistency test of local-structure effects rather than as explanation for an evolving background value of $H_0$. Overall, local underdensities can affect low-redshift Hubble-rate inferences, but they do not resolve the Hubble tension within the spherical void setup considered here.

Common envelope (CE) evolution is a critical phase in the lives of binary stars, producing close binaries that are progenitors of type Ia supernovae and gravitational wave sources. Despite its importance, CE evolution remains poorly understood, largely due to the scarcity of systems with constrained pre- and post-CE properties. Here, we present a star cluster-based framework for reconstructing the evolutionary histories of white dwarf+main-sequence (WD+MS) post-CE binaries, where cluster membership can provide an independent age constraint and/or rule out a merger origin for the WD. We demonstrate this method with Alessi12-PCE, the first such binary in an open cluster with precisely determined pre- and post-CE properties. We classify the companion as an M4V and measure a WD mass of $1.06 \pm 0.02 M_{\odot}$, making it the most massive WD+MS binary associated with a cluster. A 6.99-hour periodicity detected in a light curve is confirmed as the binary orbital period via radial velocity monitoring. Combined with the WD mass, WD cooling age, and Alessi 12 cluster age, stellar evolution models imply a $5.40 \pm 0.10 M_{\odot}$ WD progenitor that entered a CE on the asymptotic giant branch (AGB). CE evolution models where convection is the dominant physical mechanism that sets $α_{\text{CE}}$ reproduce the observed orbital separation in exactly two scenarios: either a mid-AGB interaction with $α_{\text{CE}}\approx0.99$, or a late-AGB interaction with $α_{\text{CE}}\approx0.05$. Applicable to other post-CE binaries in star clusters, our new framework enables empirical constraints on CE physics inaccessible from field binaries alone.

Active Galactic Nuclei (AGNs) are one of the most powerful sources in the Universe. The accretion-liberated energy can strongly impact the surrounding environment, up to the host galaxy and beyond. Notwithstanding their ubiquitous presence, nuclear outflows are poorly characterised, mainly due to the degeneracy between their number density $n_e$ and radial location $r$, intrinsic in the photoionisation equilibrium models which are usually employed to fit the observations. This degeneracy prevents a self-consistent determination of the gas energetics and, therefore, of the efficiency in transporting the AGN energy outwards. We analyse a joint XMM-Newton and NuSTAR observation of the bright, highly-variable AGN NGC 4051. The high flux allows to perform time-resolved spectroscopy and, thus, to study the evolution of its three main ionised absorbers. Since the timescale of the gas ionisation variability depends on its number density, constraining it allows to break the density-distance degeneracy. We employ the Time-Evolving PhotoIonisation Device (TEPID) to model the temporal evolution of the outflows. We split the observation in 37 time-resolved spectra, each few kiloseconds long (total duration 160 ksec), and we fit them jointly with the time-resolved ionised spectra. We fully constrain $n_e=10^7 cm^{-3}$ and $r=10^4$ gravitational radii for the absorber with the highest opacity and intermediate ionisation. This distance is the same of the optical and UV Broad Line Region and of the soft X-ray emission lines. The fastest and most ionised absorber is at $r<600 r_G$, cospatial with the broad component of the Fe K$α$ line. The slowest and least ionised absorber is at $r \geq 3.8 \cdot 10^5 r_G$, the same distance of the cold torus and the narrow Fe K$α$. The total energy outflow rate is below $10^{-4} L_{bol}$, ruling out a meaningful mechanical impact on the host galaxy.

We argue that the back-reaction of inhomogeneities, when combined with a pure cosmological constant, produces an effective dark energy whose equation of state can evolve with time. Our analytical computation agrees with recent numerical simulations, which have shown that the back-reaction of inhomogeneities can impact dark energy around the present time. Here, its equation of state is derived from an average version of the Friedmann equations, for which the average is taken over a fixed volume of matter particles (not necessarily global). When treating the inhomogeneities as small perturbations around a homogeneous background, dark energy acquires a time dependence which reduces to a boundary term, at least at quadratic order in the scalar modes of the perturbations. Thus, it becomes negligible for a global average. On the other hand, when treating instead the spatial derivatives of the inhomogeneities perturbatively in a gradient expansion, dark energy gets the same time dependence, which no longer reduces to a boundary term. This time dependence can be significant even for a global average or when the constant spatial curvature induced by the inhomogeneities is negligible. It also keeps the same sign around the present time, thus causing dark energy to remain either always phantom or never phantom, not allowing for any crossing from one type of behaviour to the other.

Accurate cluster mass measurements are crucial for cosmology, yet conventional hydrostatic equilibrium (HSE) methods can suffer from systematic biases, particularly in dynamically disturbed systems. We present a gated recurrent unit (GRU) based deep learning framework for predicting three-dimensional mass profiles of galaxy clusters from spherically averaged intra-cluster medium (ICM) radial profiles. By treating ICM profiles as sequential data, the GRU captures radial dependencies and naturally handles profiles with different radial samplings. We train and validate the model using high-resolution hydrodynamical simulations from The Three Hundred Project, achieving unbiased mass predictions with a typical 1$σ$ scatter of $\sim$5% over most of the cluster region, significantly improving upon HSE estimates. The model provides radius-dependent uncertainty estimates and remains robust against variations in data quality and cluster morphology. When trained jointly on independent simulation suites (GIZMO-SIMBA and GADGET-X), it successfully generalises across both simulations. Feature importance analysis shows that enclosed gas mass is the dominant predictor, with pressure and temperature providing additional information on the radial mass distribution. We further apply the GRU model to X-ray observations of the REXCESS and X-COP cluster samples from XMM-Newton and compare the inferred mass profiles with HSE estimates. The HSE masses are systematically lower than the GRU predictions for the higher-mass X-COP sample, while the REXCESS sample shows mass differences that are close to zero on average. This work provides a data-driven framework for cluster mass inference that bridges simulations and observations and can be extended to multi-wavelength datasets, including Sunyaev-Zel'dovich and optical observations.

Many white dwarfs are polluted by metals, which are generally understood to be the accreted remnants of a planetary system. Modeling these systems typically assumes that the metal concentration is homogeneous throughout the white dwarf's atmosphere. However, the magnetic fields of a white dwarf may affect the accretion geometry of the white dwarf via magnetospheric accretion. Convection in the white dwarf's photosphere will then transport the metals across the surface, with a structure set by the relative sinking versus spreading timescales. In this work, we construct models for the accretion geometry, subsequent spreading, and observed pollution of magnetic white dwarfs. We show that the magnetic fields will initially concentrate the pollution into a narrow region of the white dwarf's surface. The relative spreading and sinking timescales determine whether the metals become uniformly distributed or remain confined to localized patches. If the magnetic field and spin poles are misaligned, then patchy white dwarfs exhibit periodically variable pollution signatures, which enable constraints on the patch area. We explore this model as a possible explanation for the recent detection of periodically variable pollution signatures in magnetic white dwarfs. Finally, we also demonstrate that the concentration of material due to the magnetic field may lead to systematic underestimates of the mass accretion rate onto these objects.

The redshifted 21-cm line is a promising probe of the Epoch of Reionization, during which the first generation of stars ionized the InterGalactic Medium (IGM). We aimed to constrain the IGM neutral Hydrogen fraction and spin temperature via redshifted 21-cm absorption against high-redshift radio sources. We analysed an 18-hour observation of the radio-loud quasar PSO J352.4034-15.3373 ($z = 5.84$) in the 203-222.5 MHz band. We obtained a continuum image with a $0.66$ mJy/beam rms noise and a spectrum with $3.6$ mJy/beam rms noise per 390 kHz-wide channel. We fit the quasar spectrum with a power-law continuum modified by an intervening 21-cm absorption, testing two scenarios: an island model, a residual cold neutral Hydrogen patch surviving at the end of reionization, and a global model, approximating the overall decline of the IGM HI fraction and spin temperature with redshift. Combining archival data spanning 150 MHz to 3.0 GHz with our measurements, we determined a quasar flux density of $86.8 \pm 1.1$ mJy at 200 MHz and a spectral index of $-0.88 \pm 0.02$ across the full frequency range. We found no evidence for the 21-cm absorption from intervening neutral Hydrogen at $5.38<z<5.84$. Assuming the island model, we set a 95% confidence lower limit on the IGM spin temperature of $1.73$ K in residual HI regions. Assuming the global model, we constrained the 21-cm optical depth to $τ_{21}< 0.02$ (95% C.L.). These results provide constraints on the 21-cm optical depth near the end of reionization, over the $5.38 < z < 5.84$ range, and confirm that the IGM was heated above the adiabatic cooling limit ($\sim 0.8$ K at $z = 5.68$), consistent with theoretical predictions and with 21-cm power spectrum measurements at higher redshifts. Our results also disfavour the presence of extremely cold HI regions at $z < 5.84$ and open the way to future 21-cm absorption from high-redshift sources.

The latest measurement of the primordial deuterium abundance is in $\sim 2σ$ tension with several state-of-the-art predictions of standard Big Bang nucleosynthesis (BBN), when using the baryon density inferred from the $Λ$CDM model fit to cosmic microwave background (CMB) data. This tension increases to $\sim 3σ$ for models attempting to solve the Hubble tension, such as early dark energy (EDE), which generally predict a larger baryon density than in $Λ$CDM. We test whether this discrepancy could be pointing to a non-standard expansion history during BBN. We compute light-element abundances with PRIMAT and compare $Λ$CDM, a $ΔN_{\rm eff}$ extension, and a very early dark energy (vEDE) component. For vEDE, we sample $ΔH/H$, the fractional increase of the expansion rate while deuterium burning is freezing out and helium-4 fusion is mostly over. The Bayesian analysis using BBN plus the CMB baryon-density constraint in the EDE cosmology gives $ΔH/H = 0.087^{+0.036}_{-0.037}$ during the deuterium burning epoch, i.e. at a temperature $T_{\rm D}\simeq0.03\,{\rm MeV}$, and no residual tension. The vEDE component preserves the observed deuterium abundance at the larger CMB baryon density while only mildly affecting helium-4. By contrast, extra radiation raises the helium-4 abundance too efficiently and does not reconcile the baryon density determinations. Together with inflation, dark energy, and EDE, our results hint at the presence of another light scalar field in cosmology.

The VLBI Global Observing System (VGOS) is the next generation system for geodetic and astrometric Very Long Baseline Interferometry (VLBI). To optimize the observing time for each source in geodetic schedules, a flux density catalog is needed for the sources that are observed at the VGOS frequencies. The aim of this work is to monitor the flux densities of geodetic sources in the VGOS bands. The obtained flux density time series can be used for more effective scheduling of geodetic and astrometric VLBI experiments, as well as probing active galactic nuclei (AGN) physics. The Onsala Twin Telescopes have been used as a single baseline interferometer to measure flux densities of AGN that are part of the International Celestial Reference System (ICRF3). The telescopes observed at 3.2, 5.5, 6.6 and 10.4 GHz simultaneously. Both locally planned flux monitoring sessions and international geodetic experiments were analyzed. The data were calibrated using the Common Astronomy Software Applications (CASA). The possibility of predicting geodetic signal-to-noise ratios (S/N) using the measured flux densities was also tested. Simultaneous light curves in up to four frequencies have been obtained for 361 sources. The majority of the sources vary significantly in flux density during the measurement period. Most sources have a flat or inverted spectrum, with only 6 % having a steep spectrum. Furthermore, the flux densities from this work were shown to more precisely predict geodetic signal-to-noise ratios compared to the standard VGOS flux density catalog, especially for the most variable sources. Flux density variation needs to be taken into account to obtain the most optimal VGOS schedules. The flux density catalog presented here is expected to be of use for both astronomy and geodesy. We plan to continue the monitoring program.

We study core composition \(g_1\) modes of cold, nonrotating neutron stars containing antikaon condensates, hyperons, and \(Δ(1232)\) baryons and present, to our knowledge, the first calculation in full general relativity of the continuous-composition \(g_1\)-mode frequency and gravitational-wave damping time for stars with a \(K^-\) condensate. Using the BigApple relativistic mean-field equation of state, we compute frequencies, damping times, and frozen-composition tidal overlaps, and identify the buoyancy channels with a species-resolved Ledoux decomposition validated by mode-frequency sensitivities. We compare fully frozen matter with a fast-\(K\) limit for \(n\leftrightarrow p+K^-\) and a strong-equilibrium limit for the \(Δ\) quartet. Fast-\(K\) equilibration retains \(36\%\)--\(44\%\) of the peak local kaon buoyancy and \(65.7\%\)--\(73.4\%\) of the frozen terminal-configuration frequencies, while increasing the damping times by factors of \(14.4\)--\(31.8\); the mode remains above the nucleonic band. Strong \(Δ\) equilibration removes most of the direct \(Δ\)-induced enhancement, returning the \(NΔ\) mode toward the nucleonic band, whereas the high-frequency \(NYΔ\) branch survives through the frozen \(Λ\) gradient. Eigenfunction tracking confirms a continuous \(g_1\) branch, and representative DD-ME2 calculations reproduce this hierarchy. The direct full-GR frozen-composition phase shifts satisfy \(|ΔΦ_{g_1}|\leq1.410\times10^{-3}\) rad, a factor of 21 below the \(0.03\)-rad favorable-event scale for the Einstein Telescope. An exotic species therefore produces a distinct composition mode only if its composition gradient, or a coupled slowly equilibrating gradient, survives over the oscillation period.

Brown dwarfs and gas-giant planets are expected to emit coherent radio emission via the electron cyclotron maser instability (ECMI) mechanism powered by non-thermal electrons in their magnetospheres. Detection of a characteristic spectral cutoff in their cyclotron emission is likely to be the only feasible route to measure their magnetic field strengths. Previous radio measurements of a subset of cold brown dwarfs (spectral type T or methane dwarfs) have not shown such a cutoff at frequencies as high as $\gtrsim 10\,{\rm GHz}$, implying field strengths far higher than canonical expectations from dynamo scaling laws. However, it is also possible that these high-frequency emissions did not originate in the large-scale magnetic field but rather from small high-field-strength loops at the surface, which the scaling laws are not designed to predict. Here we present radio observations of a methane dwarf binary (WISEP J101905.63+652954.2) whose radio emission was first detected in an untargeted low-frequency survey, making it more likely that the emission traces the object's large-scale magnetic field. The object's spectrum shows a clear radio spectral cutoff whose location yields a polar surface field strength of around 126 gauss. Canonical dynamo scaling laws based on energy balance now over-predict the field strength for this object, but the scaling law based on Lorentz-Coriolis force balance (Elsasser number rule) is consistent with the measurement. Our results suggest that multi-frequency (MHz to GHz) monitoring of brown-dwarf electron cyclotron maser emission is essential to separately measure the `mean field' on large scales and `fluctuating' fields on smaller spatial scales in order to determine the dynamo scaling law that most accurately predicts field generation in the metallic hydrogen layer of gas giants and cold brown dwarfs.

The physical origin of cosmic acceleration remains one of the central questions in modern cosmology. The integrated Sachs-Wolfe (ISW) and Rees-Sciama (RS) effects, which arise from the evolution of gravitational potentials, provide a dynamical test of cosmic acceleration. We measure the cross correlation between the Planck temperature map of the cosmic microwave background (CMB) and a foreground-free map of the $100\,μ\mathrm{m}$ cosmic infrared background (CIB) from Y.-K. Chiang (2023), using the $k$-nearest neighbor cumulative distribution function ($k$NN-CDF). As the CIB map is reconstructed from ${\sim}600$ million Wide-field Infrared Survey Explorer galaxies extending to $z\approx2.5$, the measurement is equivalent to a galaxy-CMB cross correlation. We find evidence for a positive cross correlation, rejecting the null hypothesis of no correlation at $p=0.02~(2.3σ)$ using the $χ^2$ test. We further quantify its amplitude with $A_{k\mathrm{NN}}$, defined relative to an assumed cosmological model, and obtain $A_{k\mathrm{NN}}=0.95\pm0.20~(4.8σ)$ with respect to $Λ\mathrm{CDM}$ mock data including the ISW and RS effects. The $k$NN-CDF analysis improves the detection significance by ${\sim}20\%$ over the two-point correlation function. We also explore evolving dark energy by constructing two tomographic maps from the full CIB map; the results are consistent with $Λ$CDM. Finer tomographic reconstruction of the CIB, for example from multiband data of SPHEREx, would further tighten constraints on evolving dark energy.

A combination of recent observations and numerical simulations has called into question whether Sun's interior is characterized by strong turbulent convection, a problem known as convective conundrum. In light of a possible absence of vigorous convective motions, we examine whether the Sun's differential rotation, previously assumed to be tightly coupled to Reynolds stresses, may instead be sustained by the presence of a background latitudinal entropy gradient in thermal wind balance. By performing global hydrodynamical simulations of a rotating spherical shell representing the bulk of the solar convection zone, we demonstrate that solar-like differential rotation can be generated under a variety of thermal stratifications. This work proposes an alternative scenario for the origin of solar differential rotation that accommodates the previously reported discrepancies.

Reentrant phase transitions of accelerating anti-de Sitter black holes are known numerically, but their apparent loss at small string tension has lacked an analytic explanation. In the single-string ensemble at fixed pressure, charge, and tension, we solve the unrestricted two-phase Maxwell-turning problem for the charged slowly accelerating C-metric. Elimination forces the two horizon coordinates to coincide and yields a closed one-parameter locus. An exhaustive enumeration of the remaining equilibria establishes global phase selection throughout the physical black-hole sector. The locus exists for $0<μ<0.202602$, with no positive lower threshold. As $μ\to0$, the pressure and temperature widths of the reentrant window contract as the fourth and third powers of the tension, while the entropy gap and latent heat diverge. A two-chart blow-up gives a parameter-free limiting profile and identifies thermodynamic-volume inversion as the turning mechanism between two distinct noncritical phases. At a Maxwell boundary with fixed sheet incidence, projective Newton data of the thermodynamic jumps determine the leading coexistence profile. Their positive simple roots fix the turn count, order, and curvature signs; the C-metric realizes the primitive binomial class.

We study the effect of viscosity on the Sunyaev-Zeldovich signal in a simulated constrained Coma cluster analog. We aim to provide alternative constraints on the amount of viscosity in the ICM. We use the Coma cluster realization with different levels of viscosity from the LOWER DECKS zoom-ins of the SLOW constrained simulations. We generate mock thermal and kinetic Sunyaev-Zeldovich maps and and analyze their statistics. We compare them to Planck observations. Viscosity shows a consistent trend in thermal SZ (tSZ) profiles, increasing the signal in the center and suppressing it in the outskirts. Viscosity also has a strong effect on the tSZ power spectrum, elevating its amplitude on all scales. Comparisons with Planck observations suggest that the effective ICM viscosity is below $5\%$ of the Spitzer value. Unsharp masking reveals an effect on small scales, which are, however, not yet detectable with current observational data. The thermal Sunyaev-Zeldovich effect shows clear and consistent trends that allow us to probe the effective viscosity of the ICM. Our analysis suggests suppressed ICM viscosity below $5\%$ of the Spitzer value, consistent with previous X-ray analysis. Our results validate the strength of the SZ effect as an independent method to constrain ICM viscosity.

In this paper, we show that the robustness of black hole stability is not preserved when the perturbations are disposed on some critical values of the coupling constant in two non-minimally coupled scalar-tensor models, in particular for a number of regular black holes. Using an analytical demonstration in the near-horizon approximation, we obtain exact expressions for the critical coupling constant in two models for which the instability will occur. The numerical analysis show that these critical values are consistent with the threshold points in time-domain profiles of field perturbations. At that threshold value, the effective potential of the Regge-Wheeler equation exhibits an extremum exactly on the location of event horizon. We also show that the real part of the quasi-normal frequencies vanish in the near-horizon regime at critical coupling constant -- recently addressed as purely imaginary modes. Finally, we recover the general area quantization of the spherical black holes at that critical coupling without invoking to highly-damped mode approximation and the result is independent of a specific coupling model.

Be stars are massive main-sequence stars rotating close to their breakup rate. They possess a decretion disc of material built up due to mass loss from the star, however, there is not a consensus to the mechanism responsible for the formation of the disc because of their sub-breakup spin rates. We present the first 2D hydrodynamical simulations of the formation of a Be star decretion disc from a rapidly rotating star due to boundary layer effects that reduce the rotation rate of the disc close to the star. In our simulations with a disc aspect ratio of $h/r=0.1$, a decretion disc forms around a star rotating with $80 \%$ of the breakup rate, but fails when rotating at $70 \%$ of the breakup rate. For a thinner disc, a faster stellar spin may be needed to form a dynamically important decretion disc. We also demonstrate good agreement between 1D and 2D models. Although this work does not consider the presence of magnetic fields and the angular momentum transport is through viscosity, our results robustly show a Be star disc may be built up hydrodynamically through boundary layer effects, and may play an essential role in regulating the stellar spin.

We present precise radial-velocity (RV) observations of the K-type red supergiant HD~216946 (V424 Lac) obtained over approximately 22 years with the Bohyunsan Optical Astronomy Observatory Echelle Spectrograph (BOES). The RV measurements reveal a significant long-period variability with a period of 1365 days. To investigate its origin, we analyzed the RV data together with line-profile variations (LPVs), chromospheric activity indicators, and published photometric variability. The LPVs exhibit periods of approximately 1370--1380 days, while the Na~D lines show a similar periodicity near 1355 days, both comparable to the RV period. In contrast, the H-line indicators display longer periods of 2730--2800 days, approximately twice the RV period. The close correspondence between the RV variations and the activity-related diagnostics strongly suggests that the 1365-day RV signal is primarily linked to chromospheric activity and extended atmospheric variability rather than arising from purely Keplerian motion. Published photometric studies also report additional long-period variability, including a 1601-day long secondary-period (LSP)-like variation. The coexistence of multiple non-identical periods indicates that the observed variability of HD~216946 is unlikely to originate from a single physical mechanism. We therefore interpret HD~216946 as a multiperiodic red supergiant in which several intrinsic stellar processes coexist. The observed variability is most likely dominated by chromospheric activity and large-scale atmospheric dynamics, possibly accompanied by rotational modulation and LSP-like variability, although the presence of a low-mass stellar companion cannot be completely excluded.

We investigate the quasinormal modes of scalar and Maxwell field perturbations coupled to the Einstein tensor in generalized Nariai spacetimes. Our results show that, for both types of perturbations, the coupling introduces different critical values, which separate the frequency spectrum into distinct branches. Near these critical values, the square-root term that determines $ω_R^2$ may change sign, giving rise to a parameter interval in which the modes are purely imaginary. Away from this regime, the coupling affects the oscillatory parts of the two fields in opposite ways: $ω_R^2$ generally increases with the coupling constant $η$ for the scalar field, whereas it decreases with $η$ for the Maxwell field. The magnetic charge tends to enhance the oscillatory response, while increasing the spacetime dimension narrows the purely imaginary regime. This comparison shows analytically that the same curvature coupling can affect scalar and Maxwell perturbations in qualitatively different ways.

Improving sub-Hz sensitivity of gravitational wave (GW) detectors is important to detect heavier binary black hole mergers and study phenomena in stronger gravity fields. Torsion-bar-based GW detectors have been projected to focus on low-frequency GW. Among noise sources of GW detector, actuation noise induced by vibration of force sources and fluctuation of environmental magnetic fields is one that increases in low frequency. In this study, we propose photon-pressure actuator as a solution to isolate an actuator from seismic and magnetic noise. It can also be used as a photon calibrator. We designed an optical layout of the photon-pressure actuator having four beams independently controlled and applied it to CHRONOS experiment. Based on a realistic power control system, we estimated its maximum torque amplitude around yaw rotation axis as $1.0\times 10^{-8}$ N$\cdot$m and actuation efficiency as $6.6\times 10^{-13}$ rad/V, which are sufficiently large for controlling the CHRONOS torsion bar. The actuation noise was estimated as $5.3\times 10^{-19}$ rad ${\rm Hz}^{-1/2}$ at 1 Hz, lower than the target sensitivity of CHRONOS. Assuming its usage as a photon calibrator, the estimated systematic error was 1.14%.

We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). In this sixth paper of the series, we measure the dust and gas mass-loss rates by the pulsating Asymptotic Giant Branch (AGB) stars and red supergiants (RSGs) across the stellar disc of M33. We combined our time-averaged near-IR photometry with the multi-epoch mid-IR photometry obtained with the Spitzer Space Telescope, and employed a combination of spectral energy distribution modelling and scaling relations. We found that the mass-loss rate is approximately proportional to luminosity (birth mass), with additional weaker dependence on pulsation period and/or amplitude (reflecting stellar evolution). As a population, AGB stars contribute most to the mass return into the interstellar medium (ISM). Super-AGB stars also reach very high mass-loss rates, in excess of $10^{-4}$ M$_\odot$ yr$^{-1}$. The mass loss of RSGs appears to be subject to different modes, with rates well below, around, and well above the nuclear burning timescale. The timescale for the dominant mass loss phase is $\sim0.6$-$2\times10^5$ yr, shorter than the thermal-pulsing AGB or RSG phases. The rate at which stars return mass to the ISM, $\sim0.1$ M$_\odot$ yr$^{-1}$ is about four times lower than the star formation rate, which would deplete the current ISM mass within about a Gyr, thus requiring additional, external gas supplies to sustain the long-term future of star formation in M33.

We report on the measurement of the height-dependent time shifts of wave pulses in the lower solar atmosphere from high-resolution spectro-polarimetric observations obtained with the SUSI instrument on board the SUNRISE III balloon-borne solar observatory during its successful science flight in July 2024. The line-of-sight velocities derived from the line-core positions of 19 spectral lines in a 2 nm-wide window around the Ca II H line were used to determine the time shifts of propagating pulses at their respective formation heights. Our analysis reveals that these shifts are roughly ordered according to the computed formation heights of the respective spectral lines. A statistical analysis of the time shifts using sit-and-stare observations with a total duration of one hour reveals that wave pulses propagating upwards from near the solar surface to heights of approximately 500-700 km are most common, with average time lags of 20 s to 30 s between these heights. Also present are pulses with close-to-zero phase shifts, predominantly above intergranular lanes and areas of enhanced magnetic activity. Additionally, downward propagating wave pulses with negative time lags of 10 s to 15 s are seen, mostly above areas of enhanced magnetic activity. A common feature of all the observed pulses is that in the lower 250 km they show small time lags of zero to a few seconds, and only at higher layers do the propagating pulses become more dominant. This study demonstrates the potential of the many-line approach for investigating the height dependence of the physical conditions in the solar atmosphere.

The metric theory of spacetimes studies Lorentzian manifolds using tools of metric geometry. This is achieved via the null distance, which is a definite distance constructed from a time function on a spacetime. This enables the study of Gromov-Hausdorff-type convergence of spacetimes, a program recently initiated by Sakovich and Sormani. In this paper we study such notions of convergence for cosmological spacetimes with compact slices, i.e., $(a,b)\times M$ endowed with a Lorentzian metric $-dt^2+h_t$, where $h_t$ is a family of Riemannian metrics on the compact manifold $M$. Assuming mild extension properties of $h_t$, we first establish that these spacetimes are causally-null compactifiable and future developed. We then study monotone sequences with a uniform upper bound on the spatial diameter, obtaining uniform convergence of the null distances, as well as convergence of the associated timed metric spaces in the future developed Gromov-Hausdorff sense. Finally, we prove that causally-null compactifiable spacetimes satisfying a mild causal accessibility condition are causally-null, and relate the causally-null distance induced by the limit distance with the null distance induced by the (possibly non-smooth) limit metric tensor. Examples are provided to motivate the necessity of our hypotheses.

Detection of primordial $B$-mode polarization in the cosmic microwave background (CMB) from tensor perturbations generated during inflation is a major scientific goal of future CMB missions. Its success will strongly depend on the characterization of polarized foregrounds, a challenge that the LiteBIRD satellite aims to tackle with its 15 frequency bands ranging from 40 to 402 GHz. In this work, we forecast the ability of LiteBIRD to characterize polarized dust and synchrotron emission in the diffuse interstellar medium (ISM), at the angular power spectrum level. From simulated LiteBIRD intensity and polarization maps with different foreground complexities, we compute cross-frequency angular power spectra and fit them to dust and synchrotron spectral energy distributions, which are modeled by a modified black body and a power law, respectively. We find that LiteBIRD will be able to measure the dust temperature, dust and synchrotron spectral indices and spatial correlation with dispersions as low as $σ(T_{\rm d})\sim0.2$ K, $σ(β_{\rm d})\sim0.006$, $σ(β_{\rm s})\sim0.04$ and $σ(ρ)\sim10^{-2}$, as well as to detect and quantify deviations from the proposed parametric model due to variations of the emission properties in the three dimensions of our Galaxy. Additionally, LiteBIRD is likely to rule out the power-law model of polarized foreground angular power spectra suggested by Planck data. It will also be able to detect differences in the values of $β_{\rm d}$, $T_{\rm d}$, and $β_{\rm s}$ between $E$ modes, $B$ modes, and intensity in the diffuse ISM for the first time, highlighting the joint variations of the physical conditions and the magnetic field structure across the Galaxy. We conclude that in addition to detailed studies of CMB polarization, LiteBIRD will open a new window onto the physical conditions governing the ISM of the Milky Way.

A graviton can be converted into a phonon in a resonant bar detector. First-order perturbation theory predicts a strong enhancement of this conversion for coherent and squeezed graviton states, but the probability can exceed unity when the coherent or squeezing parameter is large. Since a conversion probability must satisfy the unitarity bound, we solve the graviton-phonon quantum dynamics exactly within the rotating-wave approximation. For an initial coherent state, we find that the conversion occurs intermittently through narrow bursts separated by intervals of strong suppression. For an initial squeezed state, the departure from perturbative behavior occurs earlier, and the conversion is strongly suppressed after its initial growth. These effects may provide signatures of quantum graviton-phonon dynamics relevant to single-graviton detection.

It is an old idea that higher-dimensional super-gravity (SuGra) is put on-shell just by imposing Bianchi identities on super-field strengths over super-spacetimes subject to super-torsion constraints. We give a modernized, rigorous account and review recent developments, pointing out how this perspective lends itself to the construction of infrared completions of SuGra by electromagnetic flux quantization in differential nonabelian cohomology theories $\mathcal{A}_{\mathrm{dff}}$ lifting the coefficient $L_\infty$-algebra $\mathfrak{l}\mathcal{A}$ of the super-Bianchi identities. After surveying necessary background, we highlight: (1.) our recent proof that solutions of 11D SuGra are equivalent to the $\mathfrak{l}S^4$-Bianchi identities on super $C$-field flux over super-torsion-free 11D super-spacetimes, (2.) how from this the nonlinearly self-dual gauge sector on 6D M5-brane worldvolumes is equivalent to the $\mathfrak{l}_{S^4}S^7$-Bianchi identity on super $B$-field flux, (3.) and the recent complete discussion of superspace dimensional reduction of this situation to 10D IIA SuGra via $\mathfrak{l}\mathrm{Cyc}(S^4)$-Bianchi identities on super NS/RR-flux, together with its extension to further reduction to 9 SuGra via $\mathfrak{l}\mathrm{Tor}(S^4)$-Bianchis on the corresponding super-fluxes. We close by indicating how this implies consistent infrared completions of 11D SuGra by $C$-field flux quantization in 4-Cohomotopy, of 10D IIA SuGra by NS/RR-field flux-quantization in a form of twisted unstable K-theory, and of M5-brane worldvolumes by $B$-field flux-quantization in twisted (twistorial) relative Cohomotopy. The latter admits geometric engineering of experimentally relevant topological quantum orders.

The gauge symmetry breaking $SU(2) \to U(1) \to Z_2 \to 1$ successively produces monopoles, strings and domain walls bounded by strings (WBS), with the elementary monopole carrying a $U(1)$ magnetic flux twice as large as the elementary string. The elementary strings and subsequently WBS emit gravitational waves, and during their decay, the WBS yield a network of composite strings that carry the same $U(1)$ flux as the monopoles. Depending on the cosmological evolution, we provide the gravitational wave spectra generated by the elementary strings and WBS, in combination with the composite strings which are either effectively stable, quasistable, or metastable. These three scenarios are also realized in the symmetry breaking chain $SU(3) \to SO(3) \to Z_2 \to 1$. Both $SU(2)$ and $SU(3)$ have appeared in the literature as flavor gauge symmetries.

The field equations of Conformal Gravity (CG) are constructed from fourth-order derivatives of the metric. While the second-order field equations of General Relativity (GR) reduce to a second-order Poisson equation in the weak-field limit, those of CG yield a fourth-order one. Despite this, works by Tanhayi, Fathi, and Takook [Mod. Phys. Lett. A 26, 2403 (2011)], Payandeh and Fathi [Int. J. Th. Phys. 51, 2227 (2012)], and Fathi, Olivares, and Villanueva [Galaxies 9, 43 (2021)] use second-order Poisson equations to generate purported solutions to CG in a weak-field limit. We demonstrate that these solutions are erroneous due to the use of second-order Poisson equations instead of appropriate fourth-order ones. We also point out other inconsistencies in the derivations of these metrics, such as the assertion that known CG (electro)vacuum solutions describe the interiors of matter distributions.

The terminal-velocity paradigm has long been used to interpret the motion and infer the distances of HVCs accreting onto the Milky Way, yet its validity under realistic Galactic conditions remains uncertain. We investigate its dynamical limits by combining analytical modelling with three-dimensional hydrodynamical simulations of clouds moving through a stratified Milky Way halo. We derive a generalized equation of motion including gravity, ram-pressure drag, a phenomenological mass-exchange model capturing mass loss and growth, and Bernoulli-driven cloud expansion. Analytical solutions for constant-property clouds provide a reference framework, while the full evolution is assessed using simulations with adiabatic physics, radiative cooling, and thermal conduction. Terminal velocity is a local equilibrium but not a global attractor: dense clouds remain quasi-ballistic over most of their trajectories and approach terminal motion only shortly before reaching the Galactic disc. Hydrodynamical effects further limit the paradigm. In adiabatic flows, instabilities rapidly disrupt the cloud, rendering the terminal-velocity description inapplicable. Radiative cooling instead promotes condensation and momentum loading, maintaining strong coupling to the background gas and restoring a terminal-velocity-like regime over extended periods, while thermal conduction mainly affects small-scale structure. Synthetic observables, including position--velocity diagrams, optical extinction, and soft X-ray emission, reproduce key features of observed HVCs such as velocity bridges and compression-driven emission. We also provide direct measurements of the effective drag coefficient for infalling clouds, finding values of order unity but strongly time-dependent. Overall, the terminal-velocity paradigm is a conditional description governed by cloud structure, mass exchange, and the ambient medium.

Pulsar glitches are thought to originate when angular momentum is transferred to the crust of the neutron star from the superfluid enclosed within, mediated by vortex avalanches. This idea has been qualitatively validated in the existing literature by simulating a star with a small number ($\sim 10^{3}$) of superfluid vortices, subject to deceleration and uniform pinning. Here, we employ the Barnes-Hut approximation to simulate up to $10^{5}$ vortices in a reasonable time. Using the new setup, we probe glitches that originate in the presence of inhomogeneous pinning. The inner crust of a neutron star is expected to crack as the star spins down, relieving stresses and resulting in rearrangements within the crustal lattice. These regions become centres for pinning with large pinning energies. Many such vortex traps are expected to exist in mature pulsars like Vela. We simulate one such star and find that the rise of the glitch is now staggered, a clear signature of the trap network. In young to middle-aged stars like PSR J0537-6910, we expect quakes which result in new traps and also unpin the vortices in existing ones. We observe that such a configuration involving the simultaneous release of several traps could introduce a bimodality in the glitch-size distribution, a feature that has previously been reported for PSR J0537-6910. Our simulations also indicate that macroscopic inhomogeneities in the distribution of vortices could spontaneously develop in a star with uniform pinning sites.

We study primordial black-hole (PBH) formation in a single-field model which passes from slow roll, through a transient ultra-slow-roll phase, into kination. Nonlinear numerical-relativity simulations are used to follow localised, initially sub-Hubble field fluctuations across the non-attractor transition, to determine the resulting super-Hubble curvature profiles, and subsequently to evolve their re-entry during kination. Within the set of initial configurations explored here, we find three qualitatively distinct outcomes, namely a patch which remains trapped in inflation, a positive-curvature overdensity, and a negative-curvature void bounded by an overdense shell. Each may form a PBH, although by a different physical mechanism. For one selected profile in each of the overdense and void channels, we measure collapse thresholds and compare them with thresholds for sinc profiles. The comparison shows that neither the central curvature nor the peak linear compaction alone provides a profile- or channel-independent collapse criterion. PBH abundances in non-attractor models must therefore be formulated in terms of the distribution of complete profiles, with the trapped, overdense, and void channels treated separately.

We study how one complex quasinormal frequency can parameterize the geometry and model-conditional thermodynamics of a prescribed family of static, spherically symmetric black holes. For a minimally coupled massless test scalar in the eikonal limit, the ratio $χ=ω_Rτ=ω_R/ω_I=2Q$ removes the overall mass scale. If $χ$ is injective in one dimensionless parameter, that parameter and the geometric scale can be reconstructed within the chosen family. The normalized metric then fixes the horizon and Hawking temperature, whereas Wald entropy requires the gravitational action. For the RN-form family, $χ$ determines $u=q^2$ but not the sign of charge. The constant-coupling static MOG metric is exactly RN under $\mathcal M=(1+α)m_{\rm MOG}$ and $u=α/(1+α)$; consequently, the complete minimally coupled scalar spectrum is identical on mapped backgrounds for every multipole and overtone. The two assignments have equal temperature but different action-dependent entropy. Chebyshev and WKB--Padé calculations quantify the finite-multipole error, with a maximum eikonal ratio error of $2.1\times10^{-3}$ on the tested $l=2$ RN grid. The construction is therefore a model-dependent inverse, not a theory selector. Applying it to gravitational-wave observations requires the appropriate tensor, vector, and scalar perturbation sectors beyond the test-field eikonal approximation.

The solar-neighbourhood star-formation history (SFH) can be constrained from the colour-magnitude diagram (CMD) of non-degenerate stars and tested independently with the white-dwarf luminosity function (WDLF). These two tracers sample complementary evolutionary phases and provide a consistency check on both the recovered SFH and the adopted WD cooling models. We reconstruct the local SFH from the Gaia DR3 CMD and test whether the resulting history reproduces the observed 40 pc WDLF. We fit non-degenerate stars in a cylinder of radius 200 pc and vertical extent $\pm40$ pc using the SFERA synthetic-population code. The fit is performed with the PISA and PARSEC stellar libraries. Each CMD-derived solution is then used to generate a synthetic WD population for comparison with the 40 pc WDLF, adopting the same initial-final mass relation and four WD cooling model sets: BaSTI, MIST, La Plata, and Montreal. The two CMD-based solutions agree on the main features of the local SFH: low activity at the oldest ages, an early episode around 9-11 Gyr ago, reduced activity between about 4 and 9 Gyr, and enhanced star formation over the last few Gyr. The predicted WDLFs reproduce the bright and intermediate part of the observed distribution for all cooling grids, but differ substantially around the WDLF maximum and along the faint tail. MIST and BaSTI shift too much weight to magnitudes fainter than the observed maximum, whereas La Plata gives the closest match to the faint tail but leaves larger residuals around the maximum. Montreal provides the best overall compromise. On this cooling scale, progressively removing the oldest synthetic WDs shows that the faint tail disfavours a substantial contribution from WDs with total ages older than about 11 Gyr.

Previous studies of poly-instantons in type IIB Calabi-Yau orientifolds found that these effects arise when Euclidean D3-branes wrap rigid cycles with a Wilson line. In this work, we extend this result through a general analysis of instanton zero modes, revealing the existence of new poly-instanton effects for rigid cycles with a deformation, provided that O3-planes are localised on the worldvolume of the Euclidean D3-brane. We provide concrete Calabi-Yau examples with explicit orientifold involution and brane setup. One of them is particularly well suited for realising axion hilltop quintessence. In particular, the double exponential suppression of poly-instanton effects allows to reproduce the observed vacuum energy for natural values of the underlying parameters.

In the cold dark matter paradigm, ultra-light particles are emerging as strong contenders to conventional massive particles. A unique prediction of dark matter comprising such ultra-light particles, known as fuzzy dark matter (FDM), is the presence of strong density modulations throughout galactic halos due to wave interference, which -- when approximated by a Gaussian random field (GRF) -- have been proposed to account for the inability to reproduce the observed positions (when measured at sufficient precisions) and flux ratios of multiply-lensed images of quasars. Here, we predict for the first time the properties of gravitationally lensed images generated from 3-D density fields obtained by wave simulations that directly evolve the Schrödinger--Poisson equations. Using a novel framework to project these evolved density fields along various axes of the 3-D halo, we obtain the distribution of perturbations to the positions of lensed images. As an exacting test, we find that particles of mass $10^{-22}$ eV can reproduce the positions of the quadruply-lensed radio jets in system HS 0810+2554 to a level better than that of either the GRF approximation or, to a greater extent, an NFW best-fit solution, both of which rely on accurately capturing the global 3-D density field of dark matter halos. Our work highlights the importance of wave simulations for making accurate FDM lensing predictions and the potential for high-resolution observations of lensed systems to serve as a direct probe of the nature of dark matter.

Observations by the James Webb Space Telescope reveal a population of high-redshift objects, the little red dots. These sources exhibit optical reddening alongside blue ultraviolet continua, host broad Balmer lines indicative of active black holes, and lack detectable x-ray emission. Their cosmic abundance at early epochs exceeds standard Eddington-limited growth timescales. Prevailing models invoke specific dust geometries to reconcile these traits. We propose a dust-free physical framework. We evaluate the concept that the dust-poor subset of little red dots represents the observational manifestation of hierarchically nested supermassive stars. A primary radiation-dominated envelope traps a nuclear star cluster. Plunging stars drive a magnetic dynamo that inflates the envelope. This produces the red optical continuum. Unobscured infalling stars yield the blue ultraviolet excess. Trapped stellar debris sediments to form a high-density secondary core within this Compton-thick host. This nested topology thermalizes x-rays and powers the broad hydrogen $α$ features. The central seed accretes at the global radiation limit of the host envelope. This kinetic bypass shortens the assembly timescale from hundreds of millions of years to tens of millions of years.

Daily modulation from Earth shielding provides a powerful search handle for sub-GeV dark matter (DM) in low-threshold experiments. We use this effect as a probe of interaction structure in scenarios where DM couples to both electrons and nuclei. Nuclear scattering in the Earth alters the incident DM flux, while electron scattering produces the observable ionization signal, so the total rate and modulation pattern encode different aspects of the underlying interactions. We develop this two-interaction framework for argon and xenon targets and introduce a new statistical analysis that tests the modulation shape, including the location-dependent exposure of underground detectors to different Earth-crossing trajectories, alone and in combination with the ionization spectrum. We demonstrate the method for liquid-noble detectors at underground sites SURF (USA), LNGS (Italy), and SUPL (Australia), and apply it to DarkSide-50 data as a concrete case study. Our results show that Earth-scattering modulation can help disentangle electron and nuclear DM interactions and provide a validation handle for low-threshold liquid-noble searches.

KIC 8462852, also known as Tabby's star, shows deep, irregular flux variations up to 20 per cent in its Kepler light curve. These unusual events show no apparent periodicity. Multi-wavelength observations show the dips are consistent with transiting dust, although its origin remains uncertain. The leading explanation is that dust may originate from a family of exocomets or planetesimal fragments. TESS data reveal a unique, symmetric transit event consistent with a planet or brown dwarf. This would support the theory that incoming exocometary bodies may result from orbital perturbations by a planet. The analysis of the TESS and, archival and newly obtained radial velocity (RV) data, suggests that a companion could orbit around Tabby's star with a period of at least ~1030 d. When combined with the constraints imposed by Kepler and other photometric surveys, we find only five orbital period windows are possible. We conduct observations to follow-up the first two windows, significantly reducing the allowed ranges. Fitting the TESS transit using exocometary models produces a poor fit or the need of physically unrealistic parameters, favouring the giant companion hypothesis. A 2.3 $σ$ detection of $M=9.4^{+4.9}_{-4.1}$ M$_{\mathrm{Jup}}$ (3$σ$ upper limit < 28.0 M$_{\mathrm{Jup}}$) at the transit orbital period provides tentative evidence of the companion, but more RV observations are required. Along with the radius $R=1.7\pm0.1$ R$_{\mathrm{Jup}}$, the companion would lie in the giant planet-brown dwarf regime. In the future Gaia DR4 astrometry will reveal the nature of this object.

Recent JWST observations suggest that star formation in the early universe was substantially burstier than assumed in standard models. Such burstiness can be described as a stochastic process characterized by the burst amplitude and the coherence time of star formation epochs. In this paper, we investigate how bursty star formation modifies the 21-cm power spectrum during Cosmic Dawn through its impact on the non-local radiation fields that govern its evolution, namely Lyman-$α$ and X-ray backgrounds. To do so, we introduce an unequal-time correlation in the star-formation-rate density sourcing the two fields and we compute its impact using the analytical framework implemented in the public code Zeus21. We find that the burstiness-induced time correlation produces a shot-noise-like contribution in the Lyman-$α$ and X-ray fields, enhancing both their auto- and cross-power spectra while leaving the global 21-cm signal, $T_{21}(z)$, unchanged. As a result, the 21-cm power spectrum is strongly modified by a shot-noise-like contribution at the beginning of the Cosmic Dawn, where the signal is dominated by lower-mass halos ($M_h\lesssim10^{10}\,M_\odot$), and is boosted by a factor of a few near the Wouthuysen-Field absorption trough. Elsewhere at low redshift, where the clustering signal dominates and larger halos drive the signal, the burstiness component is negligible.

We investigate cosmological inflation within the framework of a linear form of f (R, T ) gravity that incorporates an inflaton scalar field augmented by a Chern-Simons correction induced by aspects of quantum gravity. Utilizing the FLRW metric, we derive the modified Friedmann equations under the slow-roll approximations. We consider two specific forms of the Chern-Simons coupling function, trigonometric and exponential, each paired with the choice of an inflaton potential. Then, we define the essential slow-roll parameters and acquire their required expressions in the proposed model. Subsequently, we compute the scalar spectral index, the tensor spectral index, and the tensor-to- scalar ratio. By adequately constraining the free parameters, the proposed model provides accurate predictions for these inflationary observables that are in good agreement with the Planck 2018 data. Furthermore, the model predictions for the Chern-Simons exponential coupling function impose a stronger limit on the value of the tensor-to-scalar ratio and also provide good agreement with the joint Planck, BK15 and BAO data. Meanwhile, for comparative analysis and better comparison of the model motivations, we also examine the model without the Chern-Simons correction, without the linear form of f (R, T ) gravity, and with a non-linear form of f (R, T ) gravity. As a general conclusion, the obtained findings indicate that the inclusion of the Chern-Simons correction approximately refines the values of the tensor spectral index and tensor-to-scalar ratio in the context of the linear form of f (R, T ) gravity.

In arXiv:2306.01837, it was conjectured that one can engineer a large class of quantum field theory states for which the modular flow on a spacelike slice is "instantaneously local." Here we show that on null slices, such flows are highly constrained; ultraviolet universality essentially requires null-local modular flow to be unique. Concretely, we study massless Klein-Gordon theory in Minkowski spacetime, and construct, for any sufficiently regular future-directed vector field on the past null boundary of a causal diamond, a state that has this vector field as its instantaneous modular flow. We then show by explicit computation that no two distinct states in this class can be realized in the same local Hilbert space. Using a more abstract argument, we also show that in the vacuum sector of the theory, the only null-local modular flow in a causal diamond is provided by the vacuum state itself. We also comment on the construction of null-local modular flow for massive scalars, free Maxwell fields, free gravitons, and in curved backgrounds.

The cosmological propagation of gravitational waves (GWs) can exhibit amplitude and phase polarization distortions when parity symmetry is broken, a phenomenon known as cosmological birefringence. In this paper, we investigate the phenomenology of GW birefringence in a gravitational model $f(R)$ coupled to a dynamical Chern-Simons (dCS) term, analyzed in the metric and Palatini formalisms. At the background level, this model can lead to dynamical dark energy, while for GW propagation we find that the Palatini formalism predicts both amplitude and velocity birefringence, whereas the metric formalism predicts amplitude birefringence only. We also find that the birefringence effects can either be suppressed or enhanced by the $f(R)$ interactions, depending on the specific form of $f(R)$. Considering three common $f(R)$ models (Hu-Sawicki, Exponential, and Hyperbolic gravity) fit to recent cosmological data, we find that birefringence is enhanced relative to the $f(R) = R$ case, by $1-10\%$ in the Palatini formalism and up to a factor of 2 in the metric formalism. We also translate current GW birefringence constraints to bounds on the dCS coupling within our model. Finally, we show that in our model the birefringence effect grows polynomially with source redshift, in contrast to the linear-distance scaling commonly assumed in phenomenological models of GW birefringence in the current literature.

Mass loss from asymptotic giant branch (AGB) stars is the result of a complex interplay between pulsation, atmospheric dynamics, dust formation, and radiative acceleration. Pulsation periods are a key input in dynamical atmosphere and wind models, and different prescriptions for assigning periods based on stellar parameters may lead to systematic differences in the predicted wind properties. To better constrain this critical parameter, we investigated how the choice of pulsation period affects the wind properties of dynamical atmosphere and wind models of M-type AGB stars by comparing models based on an empirical period-luminosity (P-L) relation with corresponding ones that adopt a period-mean density relation derived from 3D pulsation models. We analysed two grids of DARWIN models that cover a range of current stellar masses, luminosities, and effective temperatures. For each grid, pulsation periods were assigned using either the P-L relation or the period-mean density relation, allowing for a direct comparison of the resulting dynamical structures and wind properties for pairs of models differing by period only. Independent of the adopted period prescription, the time-averaged wind properties correlate strongly with $L_\star/M_\star$. The pulsation period affects the atmospheric dynamics through changes in the relative timing of shock propagation and dust formation, which affect both wind formation and the resulting wind properties. Shorter periods favour the onset of a wind, and models differing only in pulsation period can exhibit significantly different wind properties. The period-mean density relation provides a physically motivated alternative to the empirical P-L relation by accounting for stellar parameters beyond luminosity, and enables a more direct comparison between DARWIN models and observed Mira variables.

Three-form fluxes generate a potential for the complex structure moduli in type IIB string compactifications on Calabi-Yau threefolds. In the large complex structure patch, the potential consists of a perturbative contribution and a convergent series of instanton corrections. We present examples of vacua near the boundary of large complex structure, where the minimum of the potential is essentially determined by the perturbative contribution and the first instanton correction, while the effect of all higher instantons is negligible. This phenomenon occurs when fluxes are such that the magnitude of the perturbative potential in certain directions in moduli space is of the same size as the first instanton contribution. Analysing an ensemble of flux vacua, we find that this phenomenon is statistically quite common. We also discover more subtle phenomena where instanton terms affect the multiplicity of the solutions and induce monodromy shifts.

We study gauge-field production in a post-recombination magnetogenesis scenario driven by an ultralight pseudoscalar dark matter field $φ$ coupled to electromagnetism. Previous analytical work has shown that a homogeneous oscillating $φ$ background can excite gauge field modes through tachyonic and narrow-band resonance channels. Here we follow the coupled evolution of the homogeneous $φ$ mode and gauge field modes of both helicities in an expanding background. Our numerical work confirms the results for the spectra of produced gauge particles obtained in the previous approximate analytical treatments. In addition, our study allows us to determine when back-reaction shuts off the resonance. We find that for parameter values for which the tachyonic instability band is open, back-reaction does not shut off the resonance until a fraction ${\cal{F}}$ of order one of the initial dark matter energy density has been transferred to photons, and this happens on a time scale which is short compared to the Hubble time. In the parameter range in which only the narrow resonance band is open, ${\cal{F}}$ eventually reaches order one, but the time when this happens increases as the effective coupling constant decreases, and therefore ${\cal{F}}$ may remain negligible until the present time.

Stellar contamination is a critical systematic for increasingly precise large-scale structure analyses from ongoing and next-generation surveys. Experiments targeting constraints on local primordial non-Gaussianity with $σ(f_{\rm NL}^{\rm loc}) \sim \mathcal{O}(1)$ demand sub-percent stellar contamination rates to avoid misidentifying spurious large-scale power induced by Galactic structure as true cosmological signal. In this work, we explore the use of multimodal models for star--galaxy separation, harnessing the information from both optical broad-band imaging data and SPHEREx near-infrared low-resolution spectrophotometry. The two modalities are integrated using contrastive learning, which projects image- and spectrum-based embeddings into a shared latent space. We find that classifiers trained on these transformed representations outperform those trained on the original embeddings and show less performance degradation when simpler classifiers are used. These results suggest that multimodal alignment organizes the embedding space along dimensions that are better suited to source classification. The improvement is particularly strong for image-based classification, which we connect to increased predictability of highly-discriminative infrared spectral features from the transformed image embeddings. Applying redshift error-based selections and extrapolating to the full SPHEREx footprint, we demonstrate that stellar contamination can be controlled at the sub-percent level across most of the extragalactic sky, with completeness tradeoffs largely confined to low redshift. Our work highlights the utility of multimodal methods for modern galaxy surveys such as SPHEREx and $\textit{Rubin}$ LSST.

Direct observation of the orbital motion of a sub-parsec supermassive black hole binary (SMBHB) would provide the first conclusive electromagnetic proof of such systems existing. Widely considered to be the source of gravitational waves, binaries are expected to form as a natural consequence of galactic mergers, and determining the processes that drive their evolution is essential to understanding cosmological evolution. In this work, we evaluate the prospects of using ground and spaceborne Very Long Baseline Interferometry (VLBI) to observe SMBHBs and estimate their orbital parameters. The Black Hole Explorer (BHEX) is considered the primary case study. Achieving unprecedented resolution, BHEX will provide access to a new volume of binary parameter space, potentially enabling the first confident detection of an SMBHB. We present an orbit-fitting approach that uses relative astrometry and Bayesian dynamic nested sampling, and demonstrate its efficacy on a set of example binary systems. For simulating observations, we use a binary image model based on post-Newtonian orbit propagation and find that for BHEX, binary detection requires a total flux density of 40 mJy and a minimum separation of ∼2 µas. With three annual observations, BHEX could constrain the semi-major axis and the eccentricity of binaries with orbital periods of ≤10 years to within 0.06 dex of the true values under specific noise assumptions. We have also evaluated the benefits provided by BHEX for binary detection compared to ground-only observations by arrays such as the next generation Event Horizon Telescope (ngEHT). Finally, we constrained the requirements of a future spaceborne VLBI system capable of performing a statistically significant survey of SMBHBs.

We investigate how modified electron dispersion relations affect the structure of cold white dwarfs (WDs). The deformation is introduced only in the degenerate electron equation of state, through the energy of a single particle and the group velocity, while the stellar mass density remains dominated by ions through the relation $ρ\simeq μ_e m_u n_e$ imposed by charge neutrality. The resulting equations of state are coupled to the standard TOV equations, with no modification of the gravitational field equations. For a baseline composed of carbon and oxygen with $μ_e=2$, the undeformed limit recovers a maximum mass in the Chandrasekhar scale, validating the normalization of the calculation before the modified cases are considered. The first model of modified dispersion produces only a modest stiffening over the parameter range studied, whereas the logarithmic model depends strongly on the sign of the deformation parameter: negative values increase the pressure and the maximum mass, while positive values soften the sequence. These results show that WDs can isolate the impact of modified electron kinematics on compact star structure, but the logarithmic branch in particular requires further restrictions from its physical domain, stability conditions, and observational constraints on mass and radius.

In this work, we investigate the quantum entanglement properties of analog Hawking radiation produced by a moving mirror. Using two detector modes defined through window functions on a quantum field, we quantify the bipartite entanglement established between these modes. Our results reveal that the amount of entanglement accessible to the detectors increases when the mirror follows trajectories with non-monotonic, time-dependent acceleration, which are accompanied by the emission of negative energy flux. This indicates that the negative energy flux acts as a channel through which information can be returned. To substantiate this perspective, we examine how the recovery or reconstruction of the associated partner modes is related to the negative energy flux emitted by the mirror.

Detecting planetary companions around evolved stars, particularly asymptotic giant branch (AGB) stars, is challenging due to intrinsic stellar variability such as surface convection, pulsations, and mass loss, which can produce radial velocity (RV) signals that mimic Keplerian motion. We investigate the origin of long-period, low-amplitude RV variations observed in the AGB star HD 216595 based on high-resolution spectroscopic data spanning approximately 16 years obtained with the Bohyunsan Optical Astronomy Observatory Echelle Spectrograph (BOES) and the Las Cumbres Observatory Network of Robotic Echelle Spectrographs (NRES) instruments. The RV measurements reveal a statistically significant periodic signal at 567 days that can be described by a Keplerian model consistent with a substellar companion. However, no strong correlations are found between the RV variations and stellar activity indicators, including line bisectors, chromospheric activity, and photometric variability, although weak signals at similar timescales are present in some diagnostics. Given the stellar properties of HD 216595 and similarities to previously reported cases, the observed RV variations are likely related to intrinsic stellar processes, although a companion-induced origin cannot be definitively ruled out. Further progress will require improved diagnostics and more sophisticated modeling to disentangle stellar variability from genuine orbital signals.

We present a formulation of outer and inner boundary conditions for radial non-adiabatic pulsations in AGB/post-AGB envelopes in terms of local structure of pulsation equations. This approach provides a framework to construct classes of boundary condition selectors. We show that the pulsation spectrum is primarily determined by the choice of the outer boundary selector. Different choices of the two-dimensional subspace at the outer boundary lead to different types of pulsation spectra ranging from p-mode like spectra to ones including strongly excited and damped strange modes. Our results show that the outer boundary conditions control the degree of coupling between acoustic and entropy components in the solution. Selectors dominated by slow (non-acoustic) branches lead to strongly non-adiabatic behavior and emergence of strongly excited/damped strange modes, while selectors including acoustic branches result in weaker coupling and more classical looking spectra. At the inner boundary we found that it is sufficient to enforce that the solution resides in a two-dimensional subspace allowed by the local pulsation equations. This ensures regular behavior and compatibility with WKB asymptotics in deep parts of the envelope. Once this condition is met the detailed form of the inner boundary selector has only minor influence on the resulting pulsation spectrum. We also compare the obtained spectra with those obtained using standard boundary conditions to show that the variations in excitation rates of strange modes reported previously may be interpreted in terms of the subspaces selected by the outer boundary.

The light-cone (LC) effect introduces line-of-sight (LoS) statistical inhomogeneity into the 21-cm signal. Consequently, the traditional power spectrum (PS) fails to capture the full two-point statistical information. The evolving power spectrum (ePS), $P_e(k, z)$, offers an alternative that accounts for this LoS evolution. We compare the statistical power of three different summary statistics: the standard cylindrical PS $P(k_\perp,k_\parallel)$, slice-wise PS $P_s(k, z)$ (3D PS for small bandwidth LC slices), and ePS $P_e(k, z)$. We first demonstrate that $P_e(k,z)$ successfully recovers the benchmark 3D PS of coeval simulations across most $k$ and $z$, whereas the slice-wise PS recovers only at large $k$. To efficiently perform parameter inference, we train artificial neural network (ANN) emulators on $500$ LC 21-cm signals. Our forecasts incorporate cosmic variance, estimated using $50$ statistically independent realizations of the signal, alongside SKA-Low system noise for integration times of $1000$ and $104$ hrs. We find that ePS outperforms its peers, yielding $3$ and $1.4$ times tighter constraints than $P(k_\perp,k_\parallel)$ and $P_s(k,z)$, respectively. Our results establish the ePS as an optimal summary statistic for interpreting forthcoming data.

We present a diffusion-based generative model for constructing realistic galaxy catalogues from dark matter density fields. The model takes a three-dimensional dark matter density field as input and generates galaxies directly as a point cloud with positions and physical properties, including star formation rate (SFR), without identifying dark matter haloes or subhaloes. We train the model on galaxy catalogues from the IllustrisTNG hydrodynamical simulation. The generated catalogues reproduce the spatial correspondence between galaxies and the underlying dark matter field, preferentially populating dense regions and filamentary structures. They also accurately reproduce the one- and two-dimensional distributions of SFR and stellar mass, the galaxy auto-power spectrum, and the galaxy--dark matter cross-power spectrum. The model generates galaxies associated with structures below the nominal resolution of the input density field by marginalising over unresolved small-scale structure rather than relying on a resolved halo catalogue. With an optimised diffusion sampling schedule, it generates a catalogue with SFR $> 1 ~\rm M_\odot/yr$ over a $(151.3 ~\rm Mpc)^3$ volume in approximately 10 seconds on a single GPU. Our model therefore provides a practical engine for producing large mock ensembles for upcoming galaxy redshift surveys and line-intensity mapping experiments, and offers a path toward simulation-based inference that bypasses halo finding and directly connects field-level dark matter statistics to observable galaxy populations.

Chromosome maps (ChMs) are two-dimensional diagrams of UV/optical pseudocolours widely used to diagnose the multiple stellar populations (MPs) phenomenon in globular clusters. Their raw morphology is affected by the metallicity-dependent response of the photometric filters, preventing unbiased comparisons across clusters of different metallicities. We identify a cross-cluster ChM framework that accounts for this dependence, enabling an unbiased investigation of the physical drivers of MP diversity. We analyse ChMs for 23 Galactic globulars and devise a technique to correct the raw maps for the clusters' different metallicities. On the resulting "universal" ChM we define a new photometric enrichment index $S_{\rm ChM,z}$, validated against APOGEE spectroscopy. We compare this index with cluster masses, structural parameters, orbital quantities, and accretion-origin classifications. $S_{\rm ChM,z}$ correlates with the multivariate chemical abundance ranges of the enriched population and with the aluminium spread. Across the sample it increases with initial mass but correlates most strongly with a family of orbital-confinement quantities ($z_{\max}$, vertical action, apocentre, Galactocentric radius, orbital energy). The corrected ChMs provide a chemically meaningful, population-level measure of the enriched sequence. $S_{\rm ChM,z}$ does not trace a single abundance ratio but captures the cluster-to-cluster amplitude of the combined light-element variations, with particular sensitivity to the high-temperature Mg-Al/O component of proton-capture processing. Its dependence on both cluster potential depth and orbital confinement suggests that 2P chemical diversity is shaped by internal enrichment physics together with an environmental imprint, whether inherited at formation, modified by early evolution, or filtered by subsequent orbital survival.

We investigate the thermodynamic properties of the cosmological apparent horizon in Gauss-Bonnet quasi-dilaton massive gravity. We derive the modified Friedmann equations and reformulate them in standard form, thereby allowing us to study the first and second laws of thermodynamics for the apparent horizon. Both equilibrium and non-equilibrium states are considered. In the equilibrium description, the first law retains the conventional form with the Bekenstein-Hawking area law for the horizon entropy, and we show that the generalized second law is satisfied under the null energy condition. In the non-equilibrium description, the Wald entropy receives a correction from the Gauss-Bonnet coupling, and the first law acquires an additional term associated with using the Wald entropy representation of the Gauss-Bonnet sector. We demonstrate that the total entropy change is non-negative provided the null energy condition, the positive horizon temperature condition, and the Gauss-Bonnet positivity constraints $ξ(σ)\ge0$ are simultaneously satisfied. Furthermore, we investigate the holographic entropy bound $S_{\text{inside}} \le S_{\text{horizon}}$. We demonstrate that while the idealized local thermal equilibrium assumption leads to a formal saturation or apparent breakdown during dust-dominated eras, the bound is robustly preserved across all cosmological epochs when utilizing realistic physical fluid temperatures. The condition $ξ(σ)\ge0$ is shown to be compatible with the stability constraints derived from tensor perturbations in our previous work. Our results establish that Gauss-Bonnet quasi-dilaton massive gravity is a consistent modified gravity theory from the perspective of horizon thermodynamics and the holographic principle.

BabyIAXO, a pathfinder for the International Axion Observatory (IAXO), is designed to demonstrate all key technologies at scale while achieving an improvement in sensitivity over the recent CERN Axion Solar Telescope (CAST) experiment by approximately a factor of five. Such improvement is enabled by the X-ray optics, which allow for maintaining a high signal-to-noise ratio at the detector despite a cross-sectional area of the magnetic bore being over 250 times larger than that of CAST. The optic employs a hybrid design consisting of co-aligned inner core and outer corona optics that share a common optical axis and vacuum vessel but differ in focal length and manufacturing approach. Both are segmented glass optics, with the inner core fabricated from thermally slumped borosilicate glass and the outer corona from cold-slumped Corning Willow glass. To fabricate the inner-core optic, leveraging techniques developed for NuSTAR and HEFT optics, we reoptimized and streamlined the thermal-forming procedure. The quality of free-standing glass substrates was characterized by laser metrology, X-ray reflectometry, and atomic force microscopy. We developed a cutting technique that produces smooth edges at the micron scale. We used flat stacks of glass-epoxy-graphite layers to evaluate the performance of the epoxy bondline. The optic is expected to achieve an on-axis point spread function (PSF) with a half-power diameter (HPD) of < 90", enhancing the signal-to-noise ratio by more than 55 times.

Dark Energy (DE) and Dark Matter (DM) are among the greatest mysteries in particle physics and cosmology, since their origins remain unclear. It is intriguing to consider whether both may originate from a purely gravitational sector. We propose that they arise from degrees of freedom associated with the partners of the Brans-Dicke boson in No-Scale Gravity, a fundamental scale-invariant gravitational theory in which the Planck scale is illusional. We consider the Brans-Dicke boson, together with two scalar fields, to form a vector multiplet under an $O(3)$ symmetry, whose angular directions in the Einstein frame are identified with DM and DE. Small explicit breaking of $O(3)$ generates their masses and interaction, and we show that the resulting model reproduces the required background cosmological evolution and present-day abundances, with the lighter field providing a dynamical DE component at late times. Although the DE field remains canonical, the interacting cosmology exhibits an effective phantom-like evolution at late times, of the type suggested by DESI in combination with other cosmological probes, without introducing a fundamental phantom degree of freedom. The model provides a first-principles realization of interacting DE, in which DM, DE, and their coupling emerge from the symmetry structure of the underlying gravitational theory.

A sixth-order gravity, which involves not only two leading terms, $γ_1 R\Box R$ and $γ_2 R_{μν} \Box R^{μν}$, but also quadratic curvature terms along with cubic curvature ones, will be investigated in this paper to see if it admits an exact stable de Sitter solution. First, we will derive sixth-order differential field equations of this gravity under the homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker background spacetime, using the effective method based on the Euler-Lagrange equations. Then, we will analytically solve these field equations to figure out an exact de Sitter solution, which turns out to be equivalent to a fixed point of the corresponding dynamical system of the studied gravity. Interestingly, two coefficients, $γ_1$ and $γ_2$, do not contribute to the value of the obtained de Sitter solution. However, they affect on the stability of the de Sitter solution. In particular, if these two coefficients obey the following inequality, $3γ_1+γ_2 <0$, then the de Sitter solution will always be unstable. Furthermore, numerical calculations will be performed to verify that the de Sitter fixed point is indeed a repeller of the dynamical system once this inequality is satisfied. All these results indicate that the sixth-order gravity is more suitable for an inflationary phase of early universe. To be complete, two special limits of the studied gravity model, in which field equations are reduced to second-order and fourth-order, respectively, will be investigated. As expected, only the second-order limit can always give raise a stable de Sitter solution, compatible with an accelerated expansion of late-time universe.

We investigate the correspondence between voids identified in the 3D halo distribution and those detected in WL convergence maps. We used 108 realizations of the full-sky lensing simulations, populated with a source galaxy redshift distribution consistent with the Dark Energy Survey Year 3 sample. Catalogs of 3D halo voids and WL voids were constructed using the VIDE and tunnel algorithms, respectively. The spatial association between the two populations was quantified by measuring the angular excess number density of halo voids around WL void centers. We detected a statistically significant (S/N >= 25) positive correlation between WL voids and low-redshift halo voids (0 < z_hv < 0.5) at small angular separations, indicating that WL voids trace genuine underdensities in the large-scale matter distribution. The correlation amplitude closely depends on the WL void selection scheme and decreases when stringent peak-amplitude thresholds are applied, thereby reducing the number of detected WL voids and broadening their effective sizes. The signal also displays a strong redshift dependence: halo voids at higher redshift exhibit weaker correlations because of the declining efficiency of the WL kernel, while WL voids identified from higher-redshift source bins produce stronger correlations due to the increased contribution from line-of-sight structures. We additionally examined the impact of halo-void morphology and found that rounder voids with a weaker alignment along the line of sight display marginally stronger associations with WL voids. Our results provide new insights into the contribution of 3D structure to WL-selected underdensities and offer guidance for future observational analyses seeking to interpret WL voids as tracers of the matter field.

WISPIT 2 is a young pre-main-sequence star hosting a multi-ringed transition disk and two directly imaged protoplanets, including the accreting WISPIT 2b, making it the closest known analogue to PDS 70. We present the first optical spectrum of its central star, obtained with HFOSC on the 2-m Himalayan Chandra Telescope, and derive its atmospheric parameters, test its youth, and constrain its accretion state. We analyse low-resolution spectra with iSpec and validate the pipeline at HFOSC resolution against Gaia FGK Benchmark Stars and K-type pre-main-sequence templates. We measure T_eff = 4551 +/- 150 K, log g = 4.32 +/- 0.18, and a low-resolution, model-dependent global metallicity [M/H] = -0.17 +/- 0.16. The surface gravity and Li I equivalent width support the pre-main-sequence nature of the host. H-alpha remains in net absorption but is partially filled by weak emission at only 1.5-2.0 sigma, approximately 1.1 dex below the expected chromospheric-noise level and therefore consistent with chromospheric activity rather than detectable accretion. We place a 95% upper limit on the stellar accretion rate of 3.6 x 10^-11 solar masses per year, below even the lowest monitored value for PDS 70 and implying a host-to-planet accretion-rate ratio below approximately 18. Both known double-protoplanet hosts therefore show strongly suppressed or undetectable stellar accretion. Larger spectroscopic samples are needed to determine whether this is common in multi-protoplanet transition disks.

Context. Wide substellar companions provide important benchmarks for studying the formation and evolution of brown dwarfs and giant planets. Their association with stellar primaries also provides age and metallicity constraints that are difficult to obtain for isolated objects. Aims. We investigate the population of wide substellar companions to nearby main-sequence stars using proper motions derived from multi-epoch WISE imaging. Our sample includes 2103 stars within 20 pc and is sensitive to companions down to $\sim300$ K at separations up to 20,000 AU. Methods. We use a Bayesian Markov Chain Monte Carlo (MCMC) analysis to constrain the companion mass and semi-major axis distributions while accounting for observational selection effects, including the reduced detectability of faint companions. We assume power-law distributions, $d^2n \propto M^αa^βdM da$. Results. We derive $α=-0.21^{+0.31}_{-0.27}$, $β=-1.38\pm0.32$, and an occurrence rate of $1.07^{+0.31}_{-0.24}\%$ for companions with masses of 5--80 $M_J$ at separations of 1,000--20,000 AU. The occurrence rate increases towards smaller separations and for more massive host stars. Conclusions. The inferred companion mass distribution is consistent with previous direct imaging surveys despite differences in target selection. The power-law distributions in both mass and separation also agree with those of stellar binaries. Our sample is about an order of magnitude larger than those of previous imaging surveys, providing the most robust statistical characterisation of wide substellar companions to date. These results support the interpretation that wide substellar companions represent the low-mass extension of the stellar binary population rather than a direct extension of close-in giant planets.

We propose a first-order gauge formulation of de Sitter relativity in which the pseudo-radius l(x) is promoted to a spacetime field, locally breaking SO(4,1) to SO(3,1). Here, l(x) is a geometric compensator and dl(x) the associated order parameter. This modifies the Strong Equivalence Principle: the local vacuum follows the matter distribution instead of remaining fixed, while the propagating degrees of freedom of General Relativity are unchanged. At fixed l(x), the action is SO(3,1)-gauge invariant, but varying l(x) destroys covariance under the full translational sector of SO(4,1). Through the Inonu-Wigner contraction, abstract generators become explicit spacetime transformations, yielding nonlinear Killing vectors in both the macroscopic l tends to infinity and microscopic l tends to 0 limits. The generalized Noether theorem gives a unified energy-momentum current coupling the standard tensor to the proper conformal matter current. It vanishes identically without matter, causing the asymptotic extinction of local vacuum energy and the decay of the background to Minkowski spacetime. Independent variations yield the coupled de Sitter field equations, and we algebraically prove their equivalence to the tensorial splitting on the coordinate manifold. Gauge Bianchi identities further show that Lambda(x) is an intrinsic source of spacetime torsion, consistently identifying it with the local order parameter of the symmetry breaking. The cosmological constant problem is therefore recast, not numerically solved: deriving the decay of Lambda(x) from early-universe densities to its observed value remains future work.

We characterize traversable wormholes in Unimodular Gravity (UG) and investigate what distinguishes them from their General Relativistic (GR) counterparts. For a class of static and spherically symmetric solutions, we analyze their embedding and timelike geodesics, showing that the geodesic structure is entirely determined by the metric and is therefore identical in both theories. To identify the physical origin of their differences, we compare the source sectors required to sustain the same wormhole geometry. We find that preserving a fixed UG geometry while imposing energy-momentum conservation requires restricting the equation of state, whereas relaxing this condition introduces an effective inhomogeneous vacuum contribution. We further show that the degree of exoticity is preserved even when energy-momentum is not conserved, while departures from the GR sector are encoded in an effective inhomogeneous vacuum structure whose asymptotic behavior resembles that of a cosmological constant. Our results reinforce that UG is geometrically equivalent to GR, while its distinctive features emerge in the dynamical interpretation of the source sector. More generally, our analysis illustrates that different gravitational theories may give rise to identical spacetime geometries while requiring different sources to sustain them.

This study was motivated by the search for Planetary Nebulae (PNe) and Open Cluster (OCs) associations. Only 5 PNe are currently in Galactic OCs among the previous $\sim4,800$ OCs known. They are valuable because as cluster members their properties can be linked to their progenitor stars, something not possible for general field PNe. Since the GAIA astrometric satellite first data release, thousands of new OC candidates have been identified. This offers fresh motivation to search them as hosts for known PNe. Statistically we expect 30 OC-PN pairs to be present. We searched these GAIA candidate OCs, found by Hunt \& Reffert (2023), for known central stars of PNe (CSPNe) as a practical proxy for the PNe themselves and one suited to automated searches. We identified 1 potential CSPN (IRAS 15127-5811) of "Likely" PN [GKF2010] MN18 in the HASH database, as a claimed member of the putative cluster HSC~2686. A second cluster (Lynga~3) with similar parameters and in very close angular proximity could also be a potential host. Here we reclassify CSPN IRAS 15127-5811 as a blue supergiant with a surrounding bi-polar nebula. Nevertheless, we collected all available information on proposed member stars for both these clusters. We conclude that neither claimed cluster is real. Our results shed considerable doubt on the veracity of many newly identified OCs that have modest numbers of stellar members.

The epoch of reionization leaves detectable imprints in the thermal history of the Universe. In particular, the fast ionization fronts passing over cold gas in the cosmic web overpressurize the gas, leading to the well-established phenomenon of pressure smoothing due to the hydrodynamic response of the gas. Although the effect has been indirectly measured from the power spectra of the Lyman-$α$ forest over the past decades, very few examples exist of directly measuring the typical scale associated with this physical process. This work identifies an acoustic feature in the power spectrum of the projected peculiar velocity gradient $η$. Using toy models and linear theory, this work shows that the acoustic feature is likely strongly associated with the pressure smoothing scale. A feature at the same scale is imprinted on the small-scale flux power spectrum of the Lyman-$α$ forest at $k=0.1-1\;\mathrm{s/km}$. A methodology developed for the simulations is applied to the latest measurements of the flux power spectra at $z=4.2-5.0$ to provide the first direct measurements of the pressure smoothing scale at high redshifts, $λ_p(z=4.2) > 33.78\;\mathrm{ckpc}\;(1σ)$, $λ_p(z=4.6) = 32.36\pm8.35\;\mathrm{ckpc}$ and $λ_p(z=5.0)=31.27\pm18.28\;\mathrm{ckpc}$. This proof-of-concept study paves the way for future observational programs aimed at recovering the thermal history using small-scale observations of the Lyman-$α$ forest.

Recent detections of cyano-substituted polycyclic aromatic hydrocarbons (cyano-PAHs) highlight them as key tracers of nitrogen heterocycles in the interstellar medium (ISM). However, their infrared (IR) identification requires anharmonic vibrational radiative models that account for dynamic cooling across diverse environments. We provide IR cascade emission spectra for neutral, cationic, and anionic 1- and 2-cyanonaphthalene (1- and 2-CNN) under representative astrophysical conditions, investigating how charge states and substitution positions modulate anharmonic profiles and energy redistribution during IR cascades. Using B3LYP/N07D with Second-order Vibrational Perturbation Theory (VPT2), we computed anharmonic properties and applied an optimized microcanonical sampling algorithm to calculate vibrational density of states and model environment-dependent cascade spectra. Results show that charge states strongly tune the CN nitrile band: anion intensity is enhanced by an order of magnitude compared to neutrals, whereas cation intensity is slightly weaker. 1- and 2-CNN present distinct isomeric signatures: 1-CNN displays a complex "red-wing" structure in the 3.3-micron C-H stretch due to peri-hydrogen interactions, whereas 2-CNN yields a more symmetric profile. We evaluated the fractional energy emitted via the CN stretch relative to total cascade emissivity across charge states and environments. Combined with observed CN fluxes, these fractions provide a quantitative tool to constrain cyano-PAH abundances. By bridging laboratory benchmarks with dynamic interstellar emission, this work delivers accurate anharmonic fingerprints to guide JWST observational analysis.

Protoplanetary discs emerging from collapsing molecular clouds are capable of forming planetesimals at the water snowline during both the cloud collapse and Class II disc phases; such a scenario could be responsible for creating the carbonaceous/non-carbonaceous (CC/NC) heterogeneity observed in the Solar System, and bears important implications for emergent planetary compositions. We use 1D simulations of a viscously evolving disc coupled with cloud collapse and planetesimal formation to explore how planetesimal formation during disc build-up varies across the stellar mass spectrum. We find a keen sensitivity of planetesimal formation timing, location, and outcomes on stellar mass. Discs around all investigated stellar masses form planetesimals in the Class II phase, but only the disc around low-mass M-dwarfs ($M_{\star}=0.1 M_{\odot}$) fails to form them during the infall phase. There is also a clear chemical heterogeneity in planetesimal populations (water-wet and dry) in discs born from clouds of $M_{\rm{cloud}} \geq 0.3M_{\odot}$ . Discs around low-mass M-dwarfs form and undergo extremely fast pebble drift (t < 2 Myr), forming planetesimals well within the half-life of Aluminium-26. This leads to dehydrated planetesimals in all M-dwarf disc formation cases considered. We argue that the variation in disc evolution across stellar mass makes it hard to pinpoint a common t = 0 for all discs, and that exoplanets emerging from dehydrated planetesimals around low-mass M-dwarfs will be born volatile-poor - potentially explaining the lack of rocky world atmospheres seen by JWST.

We extend the polynomial construction of parity-violating spatially covariant gravity (SCG) to total derivative order $d=5$, where $d=d_{\mathrm{t}}+d_{\mathrm{s}}$ counts the total number of temporal and spatial derivatives. After organizing the monomials by $(d_{\mathrm{t}},d_{\mathrm{s}})$ and reducing them using integrations by parts, tensor symmetries, three-dimensional curvature identities, the Schouten identity, and the Cayley-Hamilton relation, we obtain a $59$-element basis: $2$, $40$, and $17$ monomials in the sectors $(0,5)$, $(2,3)$, and $(4,1)$, respectively. A direct inspection separates $35$ monomials containing neither the lapse velocity $\mathcal{L}_{\bm{u}}\ln N$ nor $\mathcal{L}_{\bm{u}}K_{ij}$ from $11$ lapse-velocity monomials and $13$ monomials containing higher normal derivatives of the spatial metric. The latter two sectors require a dedicated degeneracy analysis. For tensor perturbations about a spatially flat cosmological background, the acceleration-free part of the manifestly first-order-in-time sector contains $16$ basis elements, whose quadratic action depends on only four combinations of coefficients. These combinations generate helicity-odd corrections proportional to $k/a$ and $(k/a)^3$ in the kinetic and gradient functions. We derive two relations that enforce luminal phase velocity for both circular polarizations while still allowing helicity-dependent kinetic normalization and damping.

Let $(M^3, g, \mathbf{k})$ be a smooth, connected, asymptotically flat initial data set with outermost past apparent horizon. We prove the Penrose conjecture for each connected component of the boundary, assuming the dominant energy condition and the $2$-convexity condition that the sum of the two smallest eigenvalues of $\mathbf{k}$ is nonnegative. The main tool is the $σ$-inverse mean curvature flow and a monotonicity formula developed in \cite{Dong26SigmaIMCF}.

The equilibrium thermodynamics of boosted Schwarzschild black holes is worked out in a concise way and shown to agree with expectations from relativistic thermodynamics.

The Hoyle-Narlikar action-at-a-distance formulation for gravity remains one of the most mathematically rigorous attempts to incorporate Mach principle into physics. A lesser known, but no less significant, is the fact that it is also one of the first in which two point functions play a key role in determining spacetime structure, and hence, are more fundamental than the metric. We argue that these ingredients have direct relevance for modern attempts to understand fundamental, emergent, and informational aspects of quantum spacetime. The non-local description of quantum spacetime, with Planck scale $\ell_0$ as a zero-point length, provides a mechanism through which the entire universe can inform local causal structure, `a la Mach, Hoyle, and Narlikar. In this chapter, we highlight certain key aspects of the HN theory and then discuss case studies from modern research that illustrate how the quantum spacetime might realize a version of the quantum gravitational Mach principle.

Spin-orbit misalignment is increasingly observed in binary stars, but its origin remains uncertain. We study the secular spin dynamics of stellar binaries and derive the associated Cassini states. We isolate a spin-spin resonance that arises when the two stellar spin-precession frequencies become commensurate. This resonance can excite the obliquity of the secondary to high values even when the primary is only weakly tilted. Magnetic braking favors the formation of high-obliquity states, whereas tidal dissipation may suppress them. Spin-spin coupling may thus help explain the observed diversity of obliquities in young stellar binaries.