高能暂现源 · 每日文献综述

WX Cen is most likely a candidate of compact binary supersoft X-ray sources, which consists of a white dwarf (WD) and a donor star that fills the Roche lobe. Recently, this source was detected to be experiencing a rapid orbital decay at a rate of $\dot{P} =-(4.4\pm0.4)\times10^{-7}~ \rm days~\rm{yr}^{-1}$. According to the mass function and optical eclipses, the donor-star mass can be constrained to be $0.41-0.44$, $0.47-0.50$, and $0.55-0.59~M_\odot$ when the WD mass is $0.7$, $0.9$, and $1.2~M_\odot$, respectively. The observed orbital period derivative cannot be produced by the angular momentum loss due to mass loss during the accretion of the WD, magnetic braking (MB) mechanisms, including standard MB, convection and rotation-enhanced MB, and anomalous MB prescriptions. We propose that the rapid orbital decay of WX Cen is caused by the tidal torque that originates from the resonant interaction between the binary and a surrounding circumbinary (CB) disk. Detailed stellar evolution models indicate that a WD binary with a $2.5 \times 10^{-7}~M_{\odot}$ CB disk can evolve toward a WX Cen-like system, which has an orbital period derivative of $\dot{P}=-4.0\times10^{-7}~ \rm days~\rm{yr}^{-1}$ and a relatively high mass-transfer rate of $5.3\times10^{-7}~M_\odot\rm yr^{-1}$ that can trigger a stable hydrogen burning process on the surface of the WD.

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.

We investigate the collisionless kinetic structure of the upper solar atmosphere in the presence of an expanding magnetic field. We consider a stationary two-component plasma confined within an expanding magnetic flux tube and subject to gravity, self-electrostatic interactions, the Pannekoek-Rosseland electric field, and magnetic moment conservation. Starting from the Vlasov equation, we derive fully analytical expressions for the particle distribution functions, density profiles, and the parallel, perpendicular, and total temperature profiles. We show that the combined conservation of energy and magnetic moment generates a loss-cone distribution, reducing the density with respect to the corresponding unmagnetized atmosphere and producing a pronounced temperature anisotropy. For a single-temperature boundary condition, the competition between magnetic moment conservation and gravity causes the parallel temperature to develop a maximum. We derive analytical scaling laws for its location and amplitude and validate them against numerical calculations. We further show that the anisotropy persists independently of the temperature distribution at the lower boundary. In the regime of rare but intense heating events, gravitational filtering enhances the contribution of the hottest particle populations at coronal heights, while magnetic moment conservation further amplifies the resulting velocity-space anisotropy. This work provides a fully analytical kinetic description of the combined effects of gravitational filtering and magnetic moment conservation in an expanding coronal magnetic flux tube undergoing stochastic heating at its base. These results establish a theoretical framework for investigating the role of magnetic-field expansion in shaping the density and temperature structure of weakly collisional stellar coronae.

This work presents the design and performance characterization of the optical calibration systems produced for the Pacific Ocean Neutrino Experiment (P-ONE), which target gain, energy and time calibration in the detector. These systems include novel light-pulse driver circuitry based on gallium nitride field-effect transistor technology and its application to directional and isotropic, self-monitoring optical calibration instruments. A total of 330 directional light pulsers and two isotropic, 17-inch calibration modules (P-CALs) were produced for the first P-ONE line. We present the designs and performance of both the directional and isotropic calibration devices and perform detailed optical characterizations of both full-production batches. In a wavelength range of 365 ─ 520 nm, our developed driver circuits achieve emission intensities up to 10<SUP>11</SUP> photons and pulse widths as small as 1.4 ns, respectively. Light-pulse drivers and self-monitoring electronics in the P-CAL were characterized using the same experimental setup, and the instrument's optical-isotropy design was optimized in combination with a dedicated GEANT4-based simulation framework. The optimized P-CAL achieves a simulated isotropy grade of 1.00 ± 0.01 across the entire 4π solid angle range. These simulation investigations were explicitly confirmed by dedicated measurements in both air and water using two independent experimental setups, and we report the results. With this, a detailed performance estimate for deployed P-CAL modules in P-ONE was possible.

We perform four independent decompositions of the deceleration parameter $q_0$ using 1564 Type Ia supernovae (SNe Ia) from the Pantheon+ catalogue: by redshift bin, sky hemisphere, host galaxy mass, and supernova colour. Without any progenitor age correction, the full sample yields $q_m$ = - 0.062 -- far below the $Λ$CDM expectation of - 0.55 -- challenging the standard picture before any correction. Crucially, the sky hemisphere test shows the deceleration is equally strong in the CMB dipole ($q_m$ = + 1.45) and anti-dipole hemispheres (+ 1.55), directly contradicting the SRS26 anisotropy argument. Our results challenge both current interpretations.

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.

In this paper, we present a comprehensive investigation into the dynamical and thermodynamic properties of the charged Reissner-Nordström (RN) black hole (BH) in the bumblebee gravity framework, where spontaneous Lorentz symmetry breaking (LSB) occurs. To analyze the dynamical behavior, we apply the unified Teukolsky master equation within the Newman-Penrose formalism to evaluate massless field perturbations of arbitrary spins ($s=0, 1/2, 1, 3/2, 2$). By deriving the corresponding effective potentials, we compute the quasinormal modes (QNMs) frequencies using the Padé-improved 6th-order WKB approximation and the Asymptotic Iteration Method (AIM) and evaluate the greybody factors for all perturbing fields, demonstrating how the LSB parameter $L$ and the BH charge $Q$ modify the spacetime's damped oscillations and wave propagation. We further assess the observational prospects of these QNMs by determining the black-hole mass ranges accessible to current and future gravitational-wave detectors, including LISA, Virgo, and LIGO. Moreover, we investigate the modified thermodynamic structure, calculating the Hawking temperature, entropy with logarithmic thermal corrections and heat capacity. Our thermodynamic analysis reveals a second-order phase transition whose critical radius is heavily governed by the background charge. These combined findings provide valuable theoretical insights into how Lorentz violation affects the physical stability, thermal evolution, and phase structure of charged BHs.

We investigate the discovery potential of the charged Higgs boson at future lepton colliders and neutrino telescopes within two simplified benchmark scenarios with universal Yukawa couplings. We demonstrate that both the muon-track and cascade events at neutrino telescopes can be exploited to search for or constrain the charged Higgs boson through resonant neutrino scattering process, and we compare the sensitivities obtained under different astrophysical neutrino flux models. We study the effect of the detector volume of neutrino telescopes on the discovery potential of the charged Higgs boson. We study the signal of charged Higgs boson at future lepton colliders over different kinematic regimes using optimized reconstruction strategies. We compare the discovery potential of the two experimental approaches over the relevant parameter space and find that future lepton colliders generally provide better sensitivity in most of the parameter space, while neutrino telescopes with very large detector volume can offer competitive and complementary sensitivity in the heavy-mass region of the charged Higgs boson.

Models of galactic-scale cosmic ray production and transport have successfully reproduced the radio and $γ$-ray spectra of many galaxies; however, one notable exception is the Large Magellanic Cloud (LMC), where models that successfully fit other galaxies consistently overestimate its $γ$-ray flux. Here we investigate this discrepancy by applying the CRIPTIC cosmic ray transport code to recent magnetohydrodynamic simulations of the LMC's interactions with the Milky Way circumgalactic medium that accurately reproduce observations of the LMC's magnetic field structure. We recover a simulated $γ$-ray luminosity that is close to the observed luminosity for a wide range of cosmic ray transport models, while our control simulations of an isolated LMC not interacting with the Milky Way show the same over-prediction problem as previous investigations. Simulations including the CGM interaction yield lower $γ$-ray luminosities because in them cosmic rays escape the galaxy primarily via advection, significantly decreasing the emission from collisional processes and changing the dominant $γ$-ray emission mechanism from pion decay to inverse Compton emission. Comparisons of the detailed spectral shape show that our interacting LMC models match the observed $γ$-ray spectrum at photon energies below $\sim 10$ GeV, but still slightly overestimate the flux at higher energies, suggesting either more strongly energy-dependent transport than the models we have explored, or a cosmic ray injection spectrum steeper than the $p^{-2.2}$ that we adopt.

RES-NOVA is a cryogenic experiment based on PbWO4 scintillating bolometers produced from archaeological lead, originally designed to detect coherent elastic neutrino-nucleus scattering (CEvNS) from galactic core-collapse supernovae. We show that the same high-density, high-Z absorbers and sub-keV energy resolution make RES-NOVA an appealing probe of solar axions. We compute the expected signal from the Primakoff, ABC (atomic recombination and de-excitation, Bremsstrahlung, Compton), longitudinal-plasmon (LP), and 57Fe nuclear-line components of the solar axion flux, folded through the inverse-Primakoff and axioelectric detection channels in PbWO4, which probe the axion couplings to photons (g_a-gamma), electrons (g_ae), and nucleons (g_aN), respectively. We derive projected sensitivities for a 1 ton*y exposure of the RES-NOVA demonstrator in the (g_ae,g_a-gamma), (g_ae,g_aN), and (g_a-gamma,g_aN) planes. The projected reach in g_ae approaches that of XENONnT to within a factor of ~2, despite a background roughly four orders of magnitude higher, thanks to the large target mass, the high-Z enhancement of the axioelectric and inverse-Primakoff cross sections, and the sub-keV energy resolution. Because the inverse-Primakoff constraint on g_a-gamma relies on absorption rather than coherent conversion, it is independent of the axion mass, unlike bounds from magnetic helioscopes. We complement these projections with the first solar-axion exclusion limit obtained on real data with a 13 g PbWO4 prototype grown from archaeological lead, using a background-model-independent optimum-interval analysis. These results establish RES-NOVA as a promising multi-coupling probe of solar axions, with simultaneous sensitivity to g_ae, g_a-gamma and g_aN that is complementary to existing helioscope and direct-detection searches.

The $Λ$ cold dark matter model successfully describes a wide range of cosmological observations. However, the persistent discrepancy between the value of the Hubble constant inferred from cosmic microwave background measurements within this model and that obtained from local distance-ladder determinations points to a significant inconsistency. This short review examines theoretical responses across the cosmological inference chain, from the gravitational field equations to the pre-recombination sound horizon and the late-time distance-redshift relation. We focus primarily on modified gravity, and briefly discuss early- and late-time mechanisms that can alter the acoustic ruler, distance measures, structure growth, or gravitational response. Current proposals can reduce the nominal tension, but often at the cost of correlated shifts in cosmic microwave background spectra, standard-ruler distances, lensing, structure growth, or calibrator information. Further progress requires unified likelihoods and multiprobe tests linking all key observables under the same model assumptions.

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.

Within theoretical frameworks such as loop quantum gravity, black holes may evolve into white holes through a quantum bounce. This paper uses general relativistic ray-tracing techniques to calculate the ray-traced imaging of accretion disks from the previous cosmic stage during the Kerr black hole and post-bounce Kerr white hole phases. Calculations show that the black hole image presents a crescent emission ring and a central shadow. In contrast, after radiation from the previous universe penetrates the rotating white hole, eccentric and asymmetric nested intensity ring structures form in the synthetic image due to frame-dragging and lensing effects. We analyze the influence of spin parameters, observation inclinations, and accretion disk geometric configurations on the distribution of this nested ring structure using synthetic images and intensity profiles. Building upon this, we introduce polarized ray-tracing calculations for radiation across evolutionary stages. This process results in the polarization image features after the polarization vector is subjected to the gravitational field and spacetime spin dragging during the photon propagation through the white hole horizon and internal spacetime. The spatial rotation patterns and concentric interference fringes in the white hole polarization images exhibit a distinct inter-ring polarization discontinuity. This phenomenon differs from the polarization behavior of black holes. The intensity ring structures and polarization inter-ring discontinuity features provide multi-band and polarimetric interferometry baselines to overcome morphological observational degeneracies. This provides theoretical guidance for future very-long-baseline interferometry (VLBI) to distinguish black holes and white holes.

This work explores the production of an MeV-scale electrophilic axion-like particles (ALPs) by utilizing the monochromatic 5.5MeV photon resulting from the nuclear fusion processes in the Sun. These 5.5MeV photons can undergo the Compton-like scattering with the ambient electrons in the solar matter to produce a substantial flux of MeV ALPs. Upon reaching the Earth, such ALPs can be detected via the same electron coupling, offering a new opportunity for the dark matter (DM) direct detection experiments to probe the previously unexplored parameter regions. We show that the existing data of LZ, PandaX-4T, and Borexino can attain the sensitivities $g_{ae} \lesssim 3.7 \times 10^{-6}$, $g_{ae} \lesssim 3.7 \times 10^{-6}$ and $g_{ae} \lesssim 1.7 \times 10^{-6}$, respectively, for $m_a \lesssim 1$MeV. An optimistic 200 tonne$\times$year exposure by PandaX-xT can reach $g_{ae}\lesssim 1.6 \times 10^{-6}$ for most of the mass window $m_a < 1$MeV and even $g_{ae} \lesssim 1.5 \times 10^{-7}$ with $m_a$ approaching 1MeV. Despite the stringent constraints from different laboratory experiments and astrophysical observations, our obtained limits from LZ, PandaX-4T, and Borexino can probe new parameter regions, specifically in the mass window $0.4\,{\rm MeV} \lesssim m_a \lesssim 1$MeV.

The radial and lateral dimensions of coronal mass ejections (CMEs) influence their duration and probability of encounter at Earth. These properties are linked to the expansion speed of CMEs in different radial and lateral directions; however, most earlier studies modeled CME evolution using a projected full ice-cream cone geometry, which does not distinguish between radial and lateral expansion. Our study investigates the asymmetric expansion (relative radial and lateral components) and kinematics of seven fast and seven slow CMEs within coronagraphic heights, using the Graduated Cylindrical Shell model. Our study confirms that CMEs expand asymmetrically, with lateral expansion exceeding radial expansion in both CME populations. This asymmetry limits the accuracy of the full ice-cream cone model. For both fast and slow CMEs, higher leading edge speeds are associated with higher expansion speeds. At a height of 10 Rs, slow CMEs with larger expansion speeds (lateral and radial) have larger angular widths (face-on and edge-on), whereas fast CMEs exhibit a negative correlation between lateral expansion speed and face-on angular width. We find that the expansion and propagation speeds of slow CMEs exhibit a two-phase evolution, whereas those of fast CMEs display more diverse trends. Overall, this study suggests that fast and slow CMEs evolve differently and should not be treated as a single population in statistical estimates of their physical parameters. Our study highlights the importance of estimating CME angular widths and expansion speeds along different directions, and beyond standard coronagraphic heights, to capture their complete physical evolution.

We construct an analytical thick-brane solution in linear teleparallel Gauss-Bonnet gravity using a first-order formalism generated by a sine-Gordon superpotential. The resulting asymptotically $\mathrm{AdS}_5$ configurations exhibit brane splitting controlled by the dimensionless parameter $q=4αk^2$. An analytical splitting condition is derived and combined with tensor-stability requirements to identify the physically viable parameter region. We show that the tensor spectrum is free of tachyonic instabilities and supports a normalizable graviton zero mode. The massive sector exhibits odd-parity gravitational resonances whose quasi-localization is significantly enhanced near the stability boundary. Our results establish a direct link between brane splitting, tensor stability, and gravitational resonances in teleparallel Gauss-Bonnet braneworlds.

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.

Hidden sectors are a generic prediction of string theory compactifications and result in a promising landscape for dark matter model building. We consider the case of hidden sector magnetic monopoles produced via a thermal phase transition in the early Universe and subsequently diluted by pair annihilation. We show that for symmetry-breaking scales $\gtrsim 100\, \text{PeV}$, the monopole abundance is unacceptably high, overclosing the Universe. Our bounds are robust against variations in the initial fraction of energy density deposited in the hidden sector, exhibiting only a weak power-law dependence on this quantity. The bound is substantially tightened in the case of multiple hidden sectors. The standard cosmology may only be recovered if one of the following is true: the hidden sector(s) are non-existent, the hidden sectors have no monopoles with symmetry-breaking scale above 100 PeV, the maximum temperature of each monopole-producing hidden sector after reheating is below its symmetry-breaking scale, or the monopole abundance is diluted during a period of early matter domination.

In this work, we investigate the existence, relation to the energy conditions, and radial bounds of static spheres in general static, spherically symmetric, asymptotically flat black hole spacetimes. By analyzing the global behavior of a radial function constructed from the mass and radial pressure functions, we prove that a static sphere necessarily requires a negative radial pressure (tension). Furthermore, we show that non-degenerate static spheres must always appear in pairs: an inner unstable sphere and an outer stable one. Assuming the Weak Energy Condition (WEC) always holds, the inner static sphere is characterized by a violation of the strong energy condition (SEC) inequality $ρ+p+2p_T<0$, where $ρ$, $p$, and $p_T$ denote the energy density, radial pressure, and tangential pressure, respectively; the SEC inequality is restored ($ρ+p+2p_T> 0$) at the outer sphere; the degenerate marginal case satisfies $ρ+p+2p_T=0$. In addition, focusing on the innermost static sphere and assuming that the WEC holds while the SEC is uniformly violated between the event horizon and this sphere, we derive a rigorous upper bound on its radius, \[ r^-_{\mathrm{sp}}\le \left[r_H^3+\frac{3r_H\bigl(1-8πr^2_Hρ(r_H)\bigr)}{8πκ}\right]^{1/3}, \] where $r_H$ is the horizon radius, $ρ(r_H)$ the energy density at the horizon, and $κ$ characterizes the strength of the SEC violation. These results establish a direct, analytic link between the energy conditions and the existence of static spheres, and provide a quantitative constraint on the matter environment of black holes possessing such orbits. The findings have potential applications in testing black hole solutions in general relativity and modified theories of gravity, as well as in interpreting related astronomical observations.

Large stellar surveys have revealed the global abundance structure of the Milky Way, but small high-fidelity spectral samples offer a critical complement of nucleosynthetic depth. We aim to access the encoded information in an ensemble of abundances by leveraging highest-quality spectra. We used HARPS spectra (R=115,000) to determine (Teff, log(g), [M/H], vmic and vsini) and 22 element abundances (Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Fe, Ni, Zn, Sr, Y, Zr, Mo, Ba, La, Ce, Nd and Eu) for 426 red giant stars at a median internal precision of $\sim$0.02 dex evaluated from analysing repeat observations of a subset of stars. Stellar parameters and line-by-line abundances were obtained using the modern spectral synthesis code Korg -- the first time it has been used for HARPS. Comparisons with the literature reveal good overall agreement. A minor 0.1 dex offset in metallicity and specific discrepancies in individual element abundances are attributed to local thermal equilibrium assumptions and inaccuracies in atomic data. We show that 22 individual elements can be collapsed into a generative 6-parameter latent-variable model of shared enrichment patterns expressed in different per-star fractions; this model accurately generates the abundances with a median $χ_{reduced}^2 = 6$. We report element gradients with respect to selected elements from different nucleosynthetic families. These gradients are a measure of inter-element production efficiencies and indicate multiple r-process production sites. Our analysis shows that abundances occupy a low-dimensional subspace, but joint (gradient-based) information encodes nucleosynthetic signatures. We have developed a Korg-pipeline to apply across evolutionary states on high-resolution spectra to provide our precision catalogue to serve as empirical constraints on chemical evolution and as a set of benchmark red giant abundance measurements.

We present a comprehensive analysis of the recently discovered TeV gamma-ray source, LHAASO J2238+5900. Based on data collected from the LHAASO, our fitting results suggest that the source is significantly extended with an angular extension of 0.54° \pm 0.01° and is spatially coincident with the pulsar PSR J2238+5903. Its spectrum is characterized by a power-law with a cutoff at 41.0\pm 3.5 TeV. Additionally, the source exhibits a significant signal of 7.9σabove 100 TeV, implying that it is a PeVatron candidate. While the gamma-ray emission is consistent with a pulsar wind nebula (PWN) scenario, the relatively large extension size also allows for a halo interpretation, potentially caused by electron-positron pairs escaping from the PWN.

Complex extremal surfaces naturally arise in holographic observables associated with timelike subregions in AdS/CFT and with holographic observables in dS/CFT, but their integration contours are generally ambiguous. In this work, we propose a method for constructing complex bulk metrics from families of complex extremal surfaces, thereby generating candidate complex geometries relevant to the gravitational path integral. This construction provides a concrete realization of how complex bulk geometry may emerge from timelike entanglement, extending the familiar idea that spacetime geometry is encoded in quantum entanglement. We use the Kontsevich--Segal--Witten (KSW) criterion as a strong consistency condition to constrain the corresponding contours. The same framework also explains why spacelike entanglement naturally selects a real Lorentzian section. In several AdS and dS examples, the KSW condition uniquely determines the admissible contour within the class considered. We also identify configurations for which the resulting complex geometry violates the KSW bound near the asymptotic boundary, revealing both the scope and the limitations of the construction. These results highlight KSW admissibility as a useful organizing principle for complex saddles in real-time holography.

A generalization of the Barboza-Alcaniz parametrization of dark energy is proposed. This is a three-parameter model which can resolve the shortcomings of the Barboza-Alcaniz behavior at future times. We show that cosmological data favor the new parametrization over both the Barboza-Alcaniz model and $Λ$CDM. We also consider the cosmological implications of the model and show that the qualitative behavior mimics to the original Barboza-Alcaniz model, with a slightly smaller acceleration rate.

In this work, we study three widely used models of f(R) gravity, namely HuSawicki, Starobinsky and ArcTanh along with the standard cosmology model ($Λ$CDM). For this, we employ the megamaser angular diameter distance and velocity measurements from the Megamaser Cosmology Project, which provide a purely geometric determination of the Hubble constant. We constrain the parameters using the Markov Chain Monte Carlo method. Our results show that values of the Hubble Constant, $H_{0}$, obtained for all four models are in concordance with its value obtained from other late-time observational data such as SNe Ia. The constraints on $H_{0}$ in all the models under study are restrictive and the marginalized estimates lie close to 73 $\mathrm {km s^{-1} Mpc^{-1}}$. The marginalized estimates of the deviation parameter, b, for the three f(R) gravity models lie close to zero. This late-time dataset, thus predicts that f(R) models mimic $Λ$CDM. However, the matter density, $Ω_m$, remains weakly constrained for all the models with its marginalized estimate close to 0.5. Further, comparison of the four models (f(R) models and $Λ$CDM) using information criteria such as Akaike Information Criterion and Bayesian Information Criterion shows that within current uncertainties, the dataset finds f(R) models statistically indistinguishable from $Λ$CDM. This is consistent with the fact that the favoured value of b for each of the f(R) models lies close to zero.

We estimate the Galaxy Stellar Mass Function (GSMF) of HI gas-rich galaxies using the 100\% ALFALFA ($α$) catalog, $\sim 98\%$ of which have optical counterparts in the Sloan Digital Sky Survey (SDSS) and a subset of them have counterparts in GALEX SDSS WISE Legacy Catalogue-2(GSWLC-2). We use the mass estimates from this subset which combines UV, optical and IR bands with individual dust corrections to recalibrate optical stellar mass estimates. We use a non-parametric method to estimate the GSMF of these gas-rich galaxies. The resulting, HI-selected GSMF is consistent with a single Schechter function with best-fit parameters $\left\{φ_* (10^{-3}\, h_{70}^{3}\,\mathrm{Mpc}^{-3}\,\mathrm{dex}^{-1}), \log_{10} (M_*/M_{\odot}) + 2\log_{10} h_{70}, α\right\} = \left\{2.30^{+0.12}_{-0.12}, \,10.83^{+0.01}_{-0.01},\, -1.14^{+0.02}_{-0.02}\right\} $. Additionally, the red and blue populations are each well described by a single Schechter function. After correcting for selection effects, we find that the red population accounts for only $\sim18\%$ of gas-rich galaxies by number, yet contributes $\sim54\%$ of the total stellar mass, with the blue population accounting for the rest. Using an optically selected sample and a joint optical-HI sample, we find gas-rich galaxies represent $\sim 33\%$ of the total stellar mass density and $\sim 39\%$ of the total galaxy number counts in the local Universe. We use the GSMF and the HI mass function (HIMF) of the HI-selected sample to obtain the $M_{\rm HI}-M_{\rm star}$ relation, which is free from selection bias.

An opacity model that incorporates improved treatments of both plasma screening and configuration interaction (CI) effects is proposed, and a 25-30% enhancement on the iron L-shell opacity is predicted at solar interior temperatures. It is originated from the plasma screening induced 14-17% enhancement on the photoionization cross sections and the CI induced 10-20% enhancement on photoexcitation and photoionization cross sections for open L-shell ions. These explain the long-standing discrepancy between theoretical and experimental iron opacity [Nature 517, 56], and the relatively weaker enhancements on chromium and nickel opacity [Phys. Rev. Lett. 122, 235001] due to the sensitivity of these effects to the different L-shell electron population and plasma temperature/density. This letter provides the systematic interpretation of L-shell opacity measurements at solar interior temperatures, and advances the accurate simulation of opacity and radiative transport in high-energy-density plasma.

Accurate modeling of polarized Galactic emission has become a major challenge for current and next-generation cosmic microwave background (CMB) $B$-mode experiments. Ignoring the spectral complexity of thermal dust and Galactic synchrotron emission when integrating along the line of sight and over large sky fractions inevitably leads to biases in CMB polarization analyses. In this work, we review how the future LiteBIRD satellite, which will benefit from an increased number of bands and sensitivity with respect to past CMB experiments such as Planck, will exploit its broader frequency coverage to characterize the spectral properties of interstellar medium emission across the three-dimensional structure of the Milky Way. We show that the canonical description of foreground spectral behavior will reach its limits for LiteBIRD, and that this challenge can be addressed using the moment expansion formalism.

We derive a new exact solution of four-dimensional Kaluza-Klein theory by applying the uplift-boost-reduction procedure to the Zipoy-Voorhees vacuum seed. The resulting Zipoy-Voorhees-dilaton spacetime is a static, axisymmetric, asymptotically flat configuration parametrised by a seed length scale $M$, the Zipoy-Voorhees deformation parameter $k$, and a boost parameter $α$ that controls the electric charge. For $k=1$ it admits a regular black-hole interpretation; for $k \neq 1$ it inherits the naked curvature singularity of the seed at $r=2M$. We extract the ADM mass, electric charge, and dilaton charge, finding that the dilaton charge obeys an algebraic constraint independent of the quadrupole deformation. The equatorial geodesics of neutral test particles and photons are studied in detail. A compact algebraic identity locates the exterior-photon-ring threshold at $k=1/2$ for all $α$, generalising the known threshold of the vacuum Zipoy-Voorhees case. The innermost stable circular orbit is mapped over the $(k,α)$ plane, and the comparison with Schwarzschild is shown to depend qualitatively on whether seed-mass or ADM-mass units are used. We further compute the gravitational redshift, which diverges on the $r=2M$ surface and renders the near-singularity orbits effectively invisible, and the critical impact parameter setting the characteristic shadow size, which in ADM-mass units shrinks below the Schwarzschild value as the charge grows.

We apply the parabolic-hyperbolic formulation of the Einstein constraint equations to generate cosmological initial data. The freely specifiable geometric data correspond to flat Friedmann--Lemaître--Robertson--Walker background, while the matter sector contains localized anisotropic perturbations of a perfect fluid. Unlike the standard approach, our method evolves the constraints outward from regular data at the origin and therefore requires no boundary conditions. This makes our method well suited as a starting point in investigating systematic biases introduced by commonly adopted boundary conditions, such as periodic boundaries. A second advantage concerns uniqueness: standard elliptic solvers may fail when multiple solutions exist, whereas solving the constraints as a well-posed evolutionary system always yields a unique solution. To demonstrate our method, we implement it numerically and generate cosmological initial data with localized anisotropic perfect fluid perturbations.

We develop a systematic analytic method for studying high-order pole-skipping in near-extremal holographic black holes. In the near-extremal regime, approaching the limit $T\to0$, the near-horizon geometry develops an approximately $\mathrm{AdS}_2 \times \mathbb{R}^{d-1}$ structure; we show that the mode index $q$ labeling pole-skipping points is identified with the IR conformal dimension $Δ_{\mathrm{IR}} = q$ in the emergent $\mathrm{AdS}_2/\mathrm{CFT}_1$ correspondence, providing a concrete physical interpretation of the subleading pole-skipping tower. The method reorganizes the near-horizon Frobenius expansion according to powers of temperature. This reveals a temperature-graded hierarchical structure that reduces the $n$-th-order pole-skipping condition to a factorized algebraic equation:each pole-skipping momentum depends only on the mode index $q$, not on the order $n$. This $n$-independence produces a high degeneracy as $T\to 0$, where pole-skipping momenta at all orders collapse onto a discrete set of values determined by near-horizon geometry and the scalar field mass; these values can be expressed in terms of thermodynamic quantities such as entropy density and specific heat. In the limit $n \gg 1$ (with $nT$ remaining small), the leading pole-skipping momenta grow asymptotically as $k_{n,n} \propto n$. We compute leading temperature corrections and verify our predictions through numerical analysis of the Dyonic Gubser--Rocha model. The results confirm that high-order pole-skipping at low temperature is governed by near-horizon physics. This provides analytic access to pole-skipping points well beyond those accessible by standard determinant methods and clarifies the structure of holographic Green's functions in the low-temperature regime.

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 demonstrate the readout of a superconducting $LC$ resonator, with $Q \approx 2 \times 10^{6}$ at approximately 250 kHz, using a dc SQUID followed by a SQUID series-array amplifier readout chain. We find that $Q$ depends on the SQUID flux-bias point, increasing near the shallow-slope point of the SQUID modulation curve and decreasing near the steep-slope point, consistent with the previously observed SQUID damping effects. From this variation, we infer the SQUID effective input impedance. We further infer the effective temperature of the resonator circuit from the resonance peak in the noise spectrum and show that it also depends on the SQUID flux-bias point, suggesting a possible contribution from SQUID back-action noise. This system provides a working prototype for future experiments based on lumped-element resonators with SQUID readout, in particular low-mass axion searches within the DMRadio program.

We investigate how the primordial curvature perturbation of a certain wavelength scale affects the halo and subhalo structure. Primordial power spectrum considered in this paper features a nearly scale-invariant form with a cutoff at the wavenumber $ k = \mathcal{O}(1)~$Mpc$^{-1}$ and an additional log-normal bump at smaller scales. We compute the host halo evolution, as well as the subhalo mass function. To be consistent with the observations of stellar streams and gravitational lensing data, the amplitude of the bump that is typically the same or larger than $10^{-9}$ of the primordial curvature perturbation should be present at the wavenumbers of $10$ - $30$ Mpc$^{-1}$.

We re-examine integration methods of linear nonadiabatic radial pulsations in the envelopes of AGB and post-AGB stars using the subspace shooting formulation. In the article the accuracy of the direct integration, the Riccati based method and a continuous renormalization nonlinear integration method are examined. The last method is not widely used in stellar pulsation studies and is therefore of interest in the present comparison. A tracking transformation of the two independent solution vectors is introduced. It helps to improve the accuracy and stability of the solution and can be readily implemented for any of these integration methods. Minimum singular value maps are used to examine the structure of the pulsation spectrum over the complex-frequency plane and also to assess the fidelity with which the integration methods transport the solution subspace. These maps provide a practical alternative to the customarily used maps based on the determinant. We use these maps together with the eigenfrequency spectra to establish mesh conditions required for the reliable transport of the solution subspace, especially in the nonlinear methods. To measure the quality of the subspace transport a spillover measure is introduced. Using this measure it is also possible to verify the placement of the inner boundary, which in the case of radial modes, cannot be guided by propagation criteria based on the Lamb frequency. Visual inspection of the eigenfrequency spectra, the singular value maps, or the eigenmode amplitudes and behavior in the deep envelope does not necessarily imply preservation of the transported-solution subspace. The spillover measure provides a much clearer indicator. This approach provides explicit quantitative diagnostics for assessing the reliability of strongly nonadiabatic pulsation calculations in AGB/post-AGB stellar envelopes.

We revisit the Affleck-Dine curvaton scenario in the framework of supersymmetry, taking Q-ball formation into account. In this scenario, a scalar field carrying baryon number, namely the Affleck-Dine field, generates both the curvature perturbations and the baryon asymmetry of the Universe. However, correlated baryon isocurvature perturbations are inevitably generated, resulting in excessively large correlated matter isocurvature perturbations. We propose a mechanism to suppress them, in which the correlated baryon isocurvature perturbations are canceled by anti-correlated dark matter isocurvature perturbations, thereby realizing compensated isocurvature perturbations. We show that the scenario can simultaneously account for the baryon asymmetry and the observed curvature perturbations of the Universe without generating excessively large matter isocurvature perturbations.

We expand the Einstein-Hilbert action to cubic order about the Schwarzschild horizon, in the even Regge-Wheeler gauge of the Gaddam-Groenenboom-'t~Hooft (GGV) near-horizon framework, and derive the cubic graviton self-interaction. Our central result is a `vanishing theorem': at leading soft order the self-coupling of the purely traceless longitudinal polarizations is identically zero, because with the trace/transverse-scalar sector switched off the fluctuation reduces to a two-dimensional block whose $\sqrt{-g}\,R$ is a total (Euler) derivative at every order in $κ$. We prove this by an explicit closed-form reduction and exhibit the cancellation term by term. It is a `framework-specific' statement, even RW gauge, GGV sector, leading soft order, not a gauge-invariant theorem of general relativity. The theorem is exact, but the quantized vertex inherits a $\sim\!20\%$ soft/scheme systematic at the only simulable multiplet ($\ell=2$), which we state explicitly. We then simulate the real-time dynamics of the resulting Hamiltonian on IBM Qiskit/Aer with exact cross-checks. Two structural facts, a conserved charge that only the cubic vertex violates, opening $φφ\to hh\to4φ$, and a provably resonance-free boost spectrum (gap $\to1/2$), already predict that the longitudinal channel is perturbatively rigid; the simulation confirms this quantitatively and measures the residual dressing ($d_{\rm eff}=1.06$; multiplicity far from thermal, Poisson, and Haar references) rather than discovering it. A symmetry-exact total-occupation truncation yields the first sector-resolved level statistics, indicative of intermediate behaviour on Hilbert spaces too small to be decisive. All circuit results agree with exact diagonalization, every headline number carries a stated systematic, and hardware execution is deferred behind a quantified noise budget.

We investigate how the particle spin modulates chaos bound violations in Lorentz-violating black hole spacetimes within the framework of Bumblebee gravity. By analyzing spinning charged particles in static spherically symmetric (A)dS black holes, we reveal the roles of spin--curvature coupling, Lorentz symmetry breaking, and the cosmological constant in shaping chaotic dynamics. The results show that the spin provides a fine-tuning mechanism for the chaos bound violation by modifying the critical angular momentum threshold, allowing particles with larger spin to access the violation regime at lower angular momenta. The Lorentz-violating parameter suppresses the violations by narrowing the allowed parameter region and reducing the critical charge. Meanwhile, the cosmological constant exhibits a dual influence: a more negative cosmological constant decreases the parameter region of violation while enhancing the violation magnitude for configurations that remain beyond the bound. These findings demonstrate that the spin and Lorentz symmetry breaking effects jointly modify the relationship between orbital instability and horizon properties.

We present the Web--Halo Model Peak--Background Split (WHM-PBS), an analytic theory in which the large-scale bias of a dark-matter halo is inherited from its cosmic-web environment. Building on the Web--Halo Model, we use the Shen \textit{et al.} moving barriers for ellipsoidal collapse generating the web hierarchy in which every halo sits inside a host filament, itself inside a sheet. Combined with the peak--background split, this picture replaces the deterministic bias--mass relation $b(M_h)$ with the bias of the host environment, averaged over the conditional mass function. As a result, halo bias $b(M_h)$ is no longer a number but a strongly skewed \emph{distribution}. In this work we make use of this distribution in three different ways: as (i) a physically motivated prior on bias relations, (ii) a prediction on halo stochasticity, and (iii) a framework for assembly bias models. Regarding (i) we find that the density bias relations $b_2(b_1)$ and $b_3(b_1)$ stay tight, while the tidal bias $b_{s^2}(b_1)$ shows significant scatter, as found in $N$-body simulations. Regarding (ii), once including halo exclusion, our model reproduces the super- to sub-Poisson shot-noise trend of Baldauf \textit{et al.} which we convert into a prior band on the EFT stochasticity amplitude parameters. Finally, regarding (iii) in the density sector it explains the bias--concentration--correlation inversion of Paranjape \textit{et al.} at the characteristic mass ($M_\mathrm{h}\simeq1.7\times10^{13}\,h^{-1}\Msun$), with no parameter tuned to assembly bias.

Observed ring-like structures in protoplanetary disks are often interpreted as local pressure maxima, which induce efficient dust concentration. We revisit this paradigm, considering the effect of the large-scale magnetic field stresses on the gas rotation speed. Our simulations show that the magnetic field can be dynamically strong and cause $1-2$% deviation from the Keplerian rotation at the periphery of a typical turbulent disk with dust grains of size $> 1\,μ$m. This effect increases the inward drift speed of large grains characterized by Stokes number of $0.01-0.1$ by up to two times in our simulations. Importantly, such MHD deviation from the Keplerian rotation does not depend on the local gas pressure gradient and leads to drift towards the star only. The fast drift induced by this effect can cancel out the outward drift caused by the positive pressure gradient at the inner edge of a ring and open up the dust trap. For the disks with turbulence parameter $α=10^{-3}$, this effect appears in the rings with a half-width of $10$ au and a density contrast up to $60$% ($200$% for $α=10^{-2}$). Thus, the presence of a large-scale magnetic field in protoplanetary disks either completely prevents or imposes stricter conditions for dust accumulation and the onset of the streaming instability in the density rings in protoplanetary disks.

CMB observations from ground-based observatories are limited in sensitivity by the fluctuating emission from the Earth's atmosphere, mostly due to water vapor inhomogeneities. Even in atmospheric windows, this spurious signal remains the major source of contamination of the data. Traditional mitigation techniques include low-frequency filtering, or for polarization measurements specifically, modulation with a rotating half-wave plate. The first method filters out a significant fraction of the target cosmological signal while the second leaves residuals due to imperfections, temperature to polarization leakage, or polarized atmospheric emission. In this work, we present a new data analysis framework, based on estimation of atmosphere emission templates using a multi-frequency focal plane. The core novelty of this setup is to have detectors dedicated to atmosphere monitoring, allowing for removing atmospheric contamination with time-domain component separation techniques. We introduce a multipole-dependent atmospheric decontamination factor $A^\mathrm{atm}_\ell$ to quantify the relative reduction of the atmospheric contamination angular power spectrum achievable with this approach. We demonstrate that this decontamination factor scales as the inverse of the survey time and that, using that criterion, our component separation pipeline can outperform a classical filter-bin map-making pipeline by a factor of 4000 for $30\le \ell \le 300$.

We formulate an obstruction and residual-completion theory for Newman-Janis-type deformations of black hole seeds, where Newman-Janis-type includes both the original complex-coordinate Newman-Janis algorithm and modified prescriptions such as non-complexification variants. The Newman-Janis algorithm is treated as an off-shell map from a static seed to a stationary-axisymmetric trial geometry, rather than as a solution-generating theorem. Its failure is encoded in a Newman-Janis obstruction tensor, defined as the residual obtained after substituting the trial configuration into the intended field equations. We decompose this residual into dynamical, geometrical/coordinate-admissibility, and source-preservation channels, separating field-equation failure from circularity, Boyer-Lindquist integrability, stress-tensor type, equation-of-state preservation, and matter-model realizability. When the obstruction is nonzero, residual completion asks whether a minimal correction of the metric and matter fields can cancel it. At leading nonzero order in the rotation parameter, this becomes a linear solvability problem: the obstruction must lie in the image of a gauge-fixed completion operator subject to boundary and source-sector constraints, while the cokernel condition gives a no-go criterion in the chosen ansatz class. We illustrate the framework with a Schwarzschild example in vacuum GR. Using an ONJA-type complexification different from the Kerr-generating one, we obtain a non-Kerr rotating trial metric and compute its obstruction. The example gives $n_\star=2$ and $\ell_\star=0$, with an additional quadrupolar component at the same order, and shows how the leading residual is removed by the minimal even-parity correction restoring the Kerr complexification. The framework replaces the search for the correct complexification rule with computable criteria for success, completion, or obstruction.

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.

We derive which-path decoherence for matter-wave interferometry that arises from tracing out the gravitons of linearized quantum gravity. Because the gravitons are driven linearly by the matter source, the branch-dependent evolution can be solved exactly, and the reduced coherence is given by the characteristic function of the initial graviton state, evaluated at the difference of the branch-induced field displacements. In vacuum, the decoherence exponent equals half the mean number of gravitons radiated by the difference source. For a smooth Gaussian trajectory, it reduces to $Γ_{\rm vac}=(8/15)\,Gm^2d^4/(\hbar c^5τ^4)$, ranging from $10^{-89}$ to $10^{-61}$ across representative matter-wave platforms. For a general squeezed graviton vacuum, we obtain an exact expression in which squeezing either suppresses or enhances the vacuum response, depending on the squeezing phase. For the strongly squeezed state produced by inflation, this expression reduces to $Γ_{\rm inf}=(π/20)\,Ω_{\rm inf}(md^2H_0/\hbar)^2$ and reaches at most $\sim10^{-27}$ for optimistic parameters. Hence, the which-path decoherence induced by radiative gravitons is therefore negligible in current matter-wave interferometers.

We investigate how, in a highly constrained system such as a four-dimensional diffeomorphism-invariant theory with vanishing bulk Hamiltonian and non-trivial interactions between the metric and additional degrees of freedom, transient excited states--called Glauber-Sudarshan states--can be constructed over supersymmetric minima. These states are generically non-supersymmetric and, although they are not minima of any potential, they admit positive-energy metric configurations that effectively mimic four-dimensional quasi-de Sitter backgrounds. We analyze how such states differ from conventional coherent states by studying their time evolution both in the canonical formalism--via boundary Hamiltonians--and in the in-in path-integral framework through Schwinger-Keldysh contours. We also examine the consistency of the construction across three complementary descriptions: the 1PI effective action, the Wilsonian (or exact renormalization group) effective action, and the Picard-Lefschetz (Lefschetz-thimble) decomposition of the Schwinger-Keldysh path integral, which provides the trans-series organization of the theory. In the presence of gauge-fixing and ghost sectors, we show that the dynamics of these transient configurations are governed by a nontrivial bootstrap relation that simultaneously constrains their behavior near supersymmetric Minkowski vacua and along quasi-de Sitter-like trajectories. Finally, we examine the Wheeler-DeWitt equation, the notion of time in the presence of transient excited states, and the emergence of the bulk Schrodinger equation. We further show that these states admit a natural structural interpretation analogous to the vertex operators that arise in the two-dimensional world-sheet formulation of string theory.

Flavor-current correlators are studied in strongly-coupled dense (holographic) matter, at finite quark chemical potential $μ_q$ and finite isospin asymmetry. The non-Abelian hydrodynamic description of the charged currents is derived in the presence of an isospin chemical potential $μ_3$. The two-point correlators of charged currents are then computed holographically at finite quark and isospin chemical potentials. In the near-extremal hydrodynamic regime, $ω, k, T, μ_3 \ll μ\equiv \sqrt{μ_q^2+μ_3^2}$, relevant for cold strongly coupled matter, the IR properties of the correlators are studied. It is shown that in this regime, the correlators agree with the non-Abelian hydrodynamic predictions. Therefore, the traditional regime of validity of standard hydrodynamics extends beyond $ω, k \ll T \ll μ$ to the so-called extended hydrodynamic regime $T\ll ω, k \ll μ$. The holographic product formula is applied to the present non-Abelian system, and is used to propose an extended hydrodynamic approximation capturing both hydrodynamic-like poles and the leading effect of AdS$_2$ poles, by resumming the low-$ω$ logarithms. The results are verified through a detailed numerical analysis of the exact correlators and quasi-normal mode spectrum.

The question of angular momentum transport by magnetic fields has recently been revived by the detection of magnetic fields in the deep interior of red giant stars. We aim at characterizing the efficiency of the transport of angular momentum and chemical elements in a stellar radiative zone subject to the magneto-rotational instability, in situations where hydrodynamical instabilities are not triggered. We use a large set of zero-net flux shearing-box simulations modelling a portion of a stellar radiative zone located close to the equatorial region. The shear is imposed in the direction of gravity, mimicking a radial differential rotation and rotation is perpendicular to gravity. We aim at establishing scaling laws between the transport efficiency and key parameters such as stratification and rotation. We obtain simulations where the MRI is triggered on the self-consistently built longitudinal field and then produces a state of self-sustained turbulence that we associate with dynamo action. We find that in the parameter range explored, both rotation and stable stratification strongly affect the vertical transport of angular momentum which is always dominated by the Maxwell stress component. In a similar way, we find that the transport of chemical composition is even more strongly affected by the stratification but less severely by rotation. Scaling laws are established and tentative extrapolations to stellar values are discussed. Transport by the stratified MRI dynamo is very promising to reconcile stellar evolution models and asteroseismic inversions of internal rotation rates of stars.

The standard "no-go theorem" against late-time solutions to the Hubble tension is essentially a normalization wall, since Baryon Acoustic Oscillation (BAO) measurements constrain the product $H_0r_d$, with $r_d$ the sound horizon at baryon drag. However, late-time solutions (which keep $r_d$ fixed) are tightly constrained not only by the BAO normalization $H_0r_d$, but also by the shape of the expansion history, i.e. the dimensionless expansion rate $E(z) \equiv H(z)/H_0$. We show that, if $r_d$ and the acoustic angular scale $θ_s$ are fixed, an increase in $H_0$ needs to be matched by an equal fractional increase in the dimensionless distance integral $I \equiv \int dz/E(z)$: $δH_0/H_0 \simeq δI/I$. We use this to quantify the "shape wall" set by relative distance constraints on $E(z)$, which we reconstruct nonparametrically, using Gaussian Processes and the latest unanchored Type Ia Supernovae (SNeIa) and BAO data. In our most conservative analysis using PantheonPlus SNeIa and DESI DR2 BAO data, we find a maximum fractional increase in $H_0$ of $\lesssim 2\%$, falling well short of the $\gtrsim 8\%$ required to solve the tension. This shape wall holds even in the presence of early-time new physics, and limits the maximum increase in $H_0$ which can be contributed by late-time modifications to $E(z)$ at fixed $θ_s$. Therefore, late-time modifications, whether invoked alone or alongside early-time new physics, face not only the well-known normalization wall, but also a stringent percent-level shape wall.

Extended bodies in general relativity do not necessarily fall along geodesics, but can be accelerated. These accelerations depend on an object's angular momentum, as well as on its quadrupole, octupole, and higher-order moments. However, these multipole moments can evolve differently from one body to another. Different bodies can thus fall differently, even with identical initial data. This paper examines how octupole moments contribute to the non-universality of free-fall in general relativity. We begin by showing that in arbitrary vacuum spacetimes, only the trace-free component of an octupole moment can affect an object's motion. It follows that at least 16 out of 40 octupole components decouple from the laws of motion. Then, we obtain two decompositions for trace-free octupole moments, one in terms of a timelike frame vector and the other in terms of a null tetrad. These decompositions are applied to motion both in generic Newtonian spacetimes and in fully-relativistic vacuum spacetimes that are of Petrov type D. In Newtonian spacetimes, the mass moments are shown to have their ordinary Newtonian effects, while the momentum moments determine a body's hidden momentum---the misalignment between its momentum and its velocity. In Petrov type D spacetimes (such as Kerr), we show that some torques that are impossible with quadrupole moments are possible with octupole moments. Octupole moments can thus have qualitatively-different effects from quadrupole moments.

We propose a relational bundle-geometric formulation of the gravitational path integral by invoking the new tool of quantum reference frames (QRFs), which in gravity are gauge-covariant coordinate systems constructed from the available field content. Formulated in terms of relational (frame-dressed) observables, this yields a manifestly gauge-invariant path integral without ghosts and anomalies, and in which observables and their correlators are local to a frame. While eliminating the need for gauge fixing, it is equivalent to Faddeev-Popov versions in which the QRF is gauge-fixed, recovering certain previous proposals. A key feature is its covariance under QRF changes: it is a perspective-neutral path integral which encodes all internal QRF perspectives and the transformations between them. This leads to several qualitative predictions: local correlators and time evolution of relational observables in one QRF perspective become fuzzy in another, and a new spectrum of relational vacua arises. Comprised of frame-dependent no-boundary and asymptotic ground states, a vacuum from one perspective appears generally excited in another. Finally, we construct gauge-invariant, yet frame-dependent effective actions by coupling sources exclusively to relational observables, setting the stage for a relational definition of renormalization.

Near-infrared CO molecular lines are suggested to be linked with dynamic processes in post-AGB stars; however, they have not been investigated at high spectral resolution. CO second overtone line variability in the H-band is presented for the cool carbon-rich post-AGB stars IRAS 22272+5435, IRAS Z02229+6208, and IRAS 20000+3239. CO features are observed to change intensity, shape, and radial velocity as well as switch between emission and absorption during the pulsation cycle. At all times, the CO line positions are located no more than around 10 km/s away from the systemic velocity. Molecular line variation is qualitatively similar in all three stars, and it appears that the site of formation is the extended atmosphere. Emission in CO lines tends to be strongest during pulsation phases close to light maximum, and weakest emission or absorption tends to be seen when close to light minimum, resembling the behaviour in CN Red and C$_2$ Swan system lines at shorter wavelengths. The connection of molecular line variability with pulsation of the star could be related to a shock that traverses the atmosphere once per pulsation cycle.

We investigate the Hilbert space structure for simple theories of gravity with $Λ>0$ on closed spatial sections. Our motivation ties to the presence of gravitational saddles in four-dimensional $Λ>0$ Einstein-Maxwell theory with $S^2\times Σ_h$ topology, where $Σ_h$ is a genus-$h$ Riemann surface. Here, as a concrete starting point, the problem is explored for two-dimensional $Λ>0$ quantum gravity. We revisit and elaborate on exact results in the matrix model literature. We study gravitational wavefunctions from both the perspective of the Wheeler-DeWitt equation and the gravitational path integral. Though simple, the setting displays many features of general interest such as large volume effects that disrupt the perturbative expansion, topological corrections to the path-integral wavefunction that offend the exact Wheeler-DeWitt equation, and a sphere path integral ${Z}^{(0)}_{\text{grav}}$ with non-trivial structure in $Λ$. We discuss candidate inner products for the infinite-dimensional canonical gravitational Hilbert space uncovered by Lian and Zuckerman. By establishing explicit results up to genus-six, we argue that the dominant contribution to the genus-$h$ gravitational disk path integral at large spatial size mimics the behavior of two-dimensional topological gravity. In passing, we show that for ${Z}^{(0)}_{\text{grav}}$ to give rise to a positive counting problem for discretised Riemann surfaces, it must have a negative pre-factor. We contrast our analysis to the more realistic case of timelike Liouville theory.