高能暂现源 · 每日文献综述

Wide binary stars provide natural laboratories for directly probing gravity in the low-acceleration regime, as dark matter inferred from any viable gravity has negligible effects on their internal dynamics. Various recent studies including Bayesian 3D analyses have shown that wide binaries with separations greater than several thousand astronomical units experience MOND-type gravity with a boost factor of $γ\approx 1.3-1.6$. However, results claiming preference for, or no deviation from, standard gravity have also been published during the same period, particularly highlighting the roles of data quality control and realistic modeling of multiple-star (i.e., triple and higher-order) systems that host hidden companion stars. Here we carefully reexamine the issues of data quality control and modeling multiple-star systems in statistical gravity tests based on sky-projected 2D velocities of wide binary stars. Through extensive tests including the acceleration-plane test, the $\tilde v$-distribution test, and the median-$\tilde v$-profile test (where $\tilde v$ is the sky-plane 2D relative velocity normalized by the Newtonian circular velocity between the two stars), we show that proper data quality control or reasonable variation in multiple-star modeling cannot remove the low-acceleration gravitational anomaly but confirms the MOND-type gravitational anomaly, particularly consistent with recent realistic MOND solutions of wide binary orbits. We find that studies claiming no evidence for the low-acceleration gravitational anomaly are consequences of bypassed calibration of the fraction of multiple-star systems using the Newtonian-regime data, bias-introduction in data quality control that is not taken into account in gravity tests, or insufficient statistics in the low-acceleration regime.

Abridged abstract: Context: Gamma-ray binaries hosting a non-accreting neutron star and a massive star exhibit multi-wavelength emission on different spatial scales. The interaction between their winds produces an outflow that can inflate a bubble or form a bow shock as it interacts with the surrounding medium. LS 5039 shows extended (1 pc-scale) X-ray emission that may arise from one of these large-scale structures. Aims: We explain and predict the large-scale emission from LS 5039. Methods: We modelled the thermal and non-thermal emission from five scenarios, representing different evolutionary phases, assuming particle acceleration at the mixed-wind termination shock: three bubble scenarios, treated with a one-zone model, and two bow-shock scenarios, studied with a multi-zone approach. We also investigated the radiation from escaping particles. Results: The extended X-rays are best explained as synchrotron radiation. Some scenarios predict detectable radio emission, while escaping particles may provide a minor steady contribution to the gamma rays in the powerful bow-shock scenario. Escaping protons with energies of 0.1-1 PeV could also inject up to $\sim10^{36}$ erg s$^{-1}$ into Galactic cosmic rays for optimistic injection luminosities. Conclusions: Gamma-ray binaries can efficiently accelerate particles on large scales, producing broadband emission and 0.1-1 PeV cosmic rays. Our results can guide future multi-wavelength observations to constrain the large-scale interaction, age, and birthplace of LS 5039.

Measuring the total mass of the Milky Way and nearby galaxy groups is difficult because classical dynamical estimators rely on assumptions about satellite orbital geometry that are rarely satisfied in practice, and because only a handful of satellite galaxies are typically available as kinematic tracers. We present a new framework that corrects the well-known Projected Mass Estimator (PME) using a residual neural network trained on thousands of simulated galaxy groups from the IllustrisTNG cosmological simulation. Separate networks are trained for each satellite sample size, from as few as 5 satellites up to 50, so that the correction automatically accounts for the statistical noise that dominates when only a small number of tracers is available. In tests on simulated halos, the classical PME systematically overestimates halo masses by factors of $M_{\rm proj}/M_{\rm true} = 1.30^{+0.72}_{-0.62}$ (using the 2D distance) and $1.46^{+0.97}_{-0.72}$ (using the 3D distance), with RMSE of 0.29 and 0.32 dex respectively. The neural-network correction reduces this to $M_{\rm proj}/M_{\rm true} = 1.02^{+0.30}_{-0.26}$ with an RMSE of 0.13 dex. Applied to the Milky Way, the method yields a total mass of $M_{\rm MW} = 1.144^{+0.399}_{-0.296}\times10^{12}\,M_\odot$, with estimates based on the brightest 5-10 satellites favoring a somewhat lower range of $(0.8$-$0.95)\times10^{12}\,M_\odot$. The modified PME gives a tighter constraint on the virial masses and the dark matter rate prediction in galaxy groups and clusters.

We investigate scalar quasinormal modes and ringdown signals of a rotating loop quantum gravity black hole constructed via the revised Newman--Janis algorithm. The spacetime incorporates two quantum parameters, the polymeric parameter $P$ and the minimal area parameter $a_0$, and reduces to the Kerr spacetime in the classical limit. Using the sixth-order WKB approximation and time-domain integration, we analyze the effective potential, quasinormal mode spectrum, and ringdown dynamics. The polymeric parameter $P$ systematically reduces the oscillation frequency $\mathrm{Re}(ω)$, while the spin parameter $a$ enhances it. The time-domain signals exhibit clear dependence on the multipole number $\ell$ and overtone index $n$. Our results provide a theoretical framework for understanding the effects of loop quantum gravity corrections on black hole perturbations and gravitational-wave ringdown signals.

We notice that Galactic sources of PeV gamma-rays are generally expected to be surrounded by multi-degree-scale extended emission produced as a result of injection of electron-positron pairs in the interstellar medium from interactions of PeV gamma-rays with microwave photons. The surface brightness of such emission may be variable in time because of variability of the PeV emission power of its parent source. A flare of the parent source produces an ``echo'' spreading across the extended emission region that may be detectable on the time scales from decades to millennia. We consider a possibility that the very extended PeV source in the Cygnus region is the produced by the Cygnus X-3 PeV gamma-ray source, possibly being an echo of its past flare.

We investigate dark matter (DM)-admixed neutron stars (NSs) within a self-consistent single-fluid relativistic mean-field framework by extending the Higgs-portal model with a massive $Z^\prime$ vector mediator. The resulting density-dependent repulsive interaction dynamically couples the baryonic matter (BM) and DM sectors, allowing the DM content to be characterized by the global particle fraction, $F_χ=N_χ/N_B$, with the local DM density determined self-consistently as $n_χ=F_χn_B$, thereby eliminating the need for the externally prescribed DM Fermi momentum adopted in previous single-fluid models. Using the NL3$ωρ$, DD2, and FSU2R EOSs, we show that increasing $F_χ$ systematically softens the nuclear equation of state (EOS), reduces the maximum NS mass by up to $\sim29\%$, increases stellar compactness, and modifies the thermodynamic response of dense matter. We further derive exact analytical expressions for the adiabatic speed of sound, its density derivative, and the adiabatic index, providing a rigorous benchmark for assessing the causality and thermodynamic stability of DM-admixed EOSs. At the microscopic level, the BM--DM interaction is shown to be dominated by the repulsive $Z^\prime$ vector channel. Our framework establishes a direct connection between collider-motivated WIMP models and the multimessenger phenomenology of NSs, with potential implications for future gravitational-wave and X-ray observations.

Collisions of ultra-relativistic bubbles during cosmological phase transitions can produce particles much heavier than the transition scale. Previous analyses modelled this process as the off-shell decay of the scalar background. We show that its results parametrically overestimate hard particle production and depend on the gauge choice and the coordinate choice in field space. We propose an alternative formalism, analogous to the partonic description of high-energy collisions. In the ultra-relativistic limit, the colliding bubbles undergo nearly free passage and hard production arises from on-shell scatterings among the quanta constituting the Lorentz-contracted walls. We apply this approach to heavy scalar, fermion, and vector particle production, and study the implications for dark matter, leptogenesis, graviton production and primordial gravitational waves.

We present new constraints on models of dark matter interacting with neutrino, based on high-resolution Lyman-$α$ forest data. We perform a suite of full hydrodynamical simulations of these models, spanning a range of interaction strengths and thermal histories. We train an emulator on the simulation results. A Monte Carlo Markov Chain analysis yields an upper limit on the interaction strength of $u_{νχ} \leq1.5\times10^{-8}$ (95% C.L.), which is the strongest direct bound to date on such interactions. Our results exclude previous hints of non-zero interactions presented in the literature. We furthermore compare our results to those obtained by mapping warm dark matter constraints to other models with suppressed small-scale structure, and find that these methods would overestimate the constraining power for this model.

The stochastic dynamics of a grain embedded within a turbulent fluid subject to strong gravitational fields can be formulated as a random walk on a Riemannian manifold. Such curvature-weighted walks provide a framework to model the intrinsic variability of accretion onto compact objects. By solving the relevant Fokker-Planck equation on a black hole background, we find the counterintuitive result that the escape probability of a grain is actually higher compared to flat space. This is a consequence of the stretching of radial cells near the event horizon: there is a greater spatial volume for the particle to wander through before being captured. By simulating a large number of grain trajectories, initially distributed on concentric shells with a density profile set by the thin-disc structure equations, we also study particle fluxes through the horizon. Shallower spectral indices emerge at low frequencies relative to flat space, primarily due to time dilation, and steeper ones at high frequencies. We find that Schwarzschild-weighted spectra broadly match observations of low-frequency X-ray variability from systems like Cygnus X-1 in their hard state, suggesting that geometric drifts may be important in describing stochastic accretion processes.

Primordial black holes (PBHs) are compelling dark matter candidates. PBHs with masses between $10^{15}$ and $10^{18}\,\mathrm{g}$ can heat interstellar dust via Hawking radiation. Previous studies of this dust heating mechanism mostly neglected PBH spin and adopted a single dark matter halo profile. In this work, we incorporate PBH spin, which substantially enhances the emitted radiation flux, and systematically investigate the dependence of constraints on the dark matter density distribution by considering five different halo models. We compute the complete photon spectra, including both primary and secondary emissions. Our results show that, for a fixed profile and mass function, larger spin parameters yield stronger constraints on the PBH fraction $f_{\mathrm{PBH}}$. Among the halo models, the Isothermal profile gives the most stringent limits, followed by Einasto, then NFW and Moore, while the Burkert profile yields the weakest constraints. For silicate grains, which cool less efficiently than graphite, the upper limits reach $\mathcal{O}(10^{-4})$ for high spin cases. We consider both monochromatic and lognormal mass functions, and find consistent trends between them. For the lognormal case, larger values of the width $σ$ lead to a broader mass range being excluded, in particular ruling out massive PBHs as the sole dark matter component. Our bounds are generally weaker than other existing limits, but they provide a complementary and independent constraint.

We present constraints on the graviton mass using the 4.5-year data release from the MeerKAT Pulsar Timing Array (MPTA) and provide forecasts for the upcoming Square Kilometre Array PTA (SKA--PTA). By modeling the modified dispersion relation and the corresponding tensor correlation function for massive gravitons, we perform Bayesian inference on the angular-correlation measurements under three noise configurations (DATA, ER, ALT). Our 90\% credible upper limits on the graviton mass are $m_g < 2.10 \times 10^{-23}\,\mathrm{eV}/c^{2}$ (DATA), $m_g < 2.58 \times 10^{-23}\,\mathrm{eV}/c^{2}$ (ER), and $m_g < 2.25 \times 10^{-23}\,\mathrm{eV}/c^{2}$ (ALT). Including monopolar and dipolar contributions does not significantly alter these bounds, confirming that the constraints are driven by the quadrupolar tensor correlation. All results remain fully consistent with general relativity. For SKA--PTA, we forecast sensitivities down to $m_g \sim 10^{-24}\,\mathrm{eV}/c^{2}$ with a 10-year observing baseline and $m_g \sim 10^{-25}\,\mathrm{eV}/c^{2}$ with a 50-year observing baseline, representing order-of-magnitude improvements over current limits. This work demonstrates the power of current and future PTA observations to test fundamental aspects of gravity in the nanohertz band.

In May 2024, NOAA active region (AR) complex 13664/8 was one of the most productive regions of the current solar cycle, producing 12 X-class flares and over 20 coronal mass ejections (CMEs) and triggering the strongest geomagnetic storm since 2003. We investigate why this AR complex was so CME-productive. Using primarily SDO/AIA and SDO/HMI observations, we analyzed its photospheric magnetic evolution, eruption sources, eruption waiting times, and magnetic parameters in comparison with five other ARs. The region initially contained only AR 13664 and exhibited limited flare activity until AR 13668 emerged on May 4, after which clustered major flares and CMEs occurred. Rapid, complex flux emergence substantially increased the region's area, magnetic flux, complexity, and nonpotentiality. The increased complexity was manifested by at least 12 emerging bipoles and 6 collisional polarity inversion lines (cPILs) formed between nonconjugated polarities, all showing sustained collision and shearing and serving as eruption sources. Decay index distributions show systematically lower critical heights (<45 Mm) above CME source regions. The CME waiting time distribution exhibits two peaks, suggesting that multiple cPILs enhanced CME productivity by increasing both recurrent CMEs from the same source and disturbance-triggered CMEs from nearby sources. These results indicate that, in addition to sufficient nonpotentiality and rapid background-field decay, high magnetic complexity accompanied by dynamical collisional shearing at multiple cPILs was crucial for the extreme CME productivity of AR 13664/8.

The collapse of false-vacuum domains during first-order phase transitions in the early Universe may lead to primordial black hole (PBH) formation whose signatures form a multimessenger complement to gravitational wave (GW) production. We focus on PBH formation through the gravitational collapse of false-vacuum domains, described using a junction condition formalism. This formalism develops the Schwarzschild collapse criterion dynamically, avoiding the usage of critical overdensity thresholds in a post-inflationary Universe, and is driven solely by the vacuum energy enclosed within shrinking false-vacuum domains without the assistance of particle or domain wall interactions in the false vacuum. We study the parameter space of phase transitions and identify regions producing observable GWs, observable PBHs, or both simultaneously. We investigate this phenomenology in polynomial and classically conformal scalar field potentials as model benchmarks. We find that the scalar fields with vacuum expectation values in the range of 1-100 MeV have the largest model parameter space available for these multi-messenger signals, which are testable with upcoming GW observatories, searches for Hawking radiation, and gravitational lensing surveys.

JWST observations, which have pushed the discovery and characterization of galaxies to cosmic dawn, have revealed significant deficiencies in state-of-the-art galaxy formation simulations, motivating the need for novel, physically grounded models. We present the first results from the Azahar suite of ten high-resolution ($\sim$20 pc), large-volume zoom-in cosmological simulations, which follow the formation of thousands of galaxies and progressively incorporate radiative transfer (RT), cosmic rays (CRs), and magnetohydrodynamics in addition to the 'standard' baryonic physics. Our Non-Thermal model, which simultaneously includes RT and CRs on the fly, reproduces the observed UV luminosity function from high redshifts ($z \sim 14$) to cosmic noon ($z \sim 3$), as well as the evolution of the stellar mass function, the galaxy main sequence, and observed gas metallicities. It does so through a combination of burstier star formation, with enhanced variability on both long ($\gtrsim 50$ Myr) and short ($\lesssim 10$ Myr) timescales, and a transition from high to low outflow mass-loading factors over cosmic time as CR pressure builds up in the ISM. We find that simple (boosted) thermal SN feedback models fail to capture the cosmic evolution of the very first galaxies because they lack realistic feedback channels that operate on different timescales and have distinct thermodynamical properties, thereby either overproducing stellar mass or driving overly explosive outflows. Our results indicate that non-thermal galaxy formation physics is crucial for providing a robust theoretical framework with which to interpret the high-redshift galaxy populations now being uncovered by JWST.

We study accretion and neutrino-sensitive thermal signatures of a static black hole reconstructed from a three-parameter generalized entropy. The construction is thermodynamic by design: the entropy deformation is not mapped to a radial-coordinate redefinition or to a prescribed Reissner--Nordström-like correction. Instead, the generalized entropy fixes the horizon response factor $Ξ_h=dS_G/dS|_{S_h}$. The effective exterior geometry is then reconstructed by requiring its surface-gravity temperature to reproduce the generalized thermodynamic temperature. As a result, the metric preserves the horizon area and the Schwarzschild asymptotics, and reduces smoothly to Schwarzschild when $Ξ_h\to1$. The deformation is controlled by $λ_G=1/Ξ_h-1$, while the integer $p\geq2$ determines the radial localization of the near-horizon correction. We compute the photon sphere, critical shadow scale, circular geodesics, ISCO, Novikov--Thorne flux, disk temperature, radiative efficiency, energy-at-infinity luminosity, a redshifted spectral proxy, and neutrino-sensitive temperature moments. In particular, positive $λ_G$ moves the photon sphere and ISCO inward, decreases the shadow scale, raises the radiative efficiency, and concentrates the energy release toward the inner disk. By contrast, negative $λ_G$ produces the opposite trend. Finally, the neutrino sector is modeled conservatively using dimensionless temperature moments instead of a full neutrino-dominated accretion flow or annihilation-deposition calculation. The hierarchy among the $ n=4$, $n=6$, and $n=9$ moments reveals that entropy-induced disk deformation becomes increasingly apparent with higher temperature exponents. Thus, observable changes in compact orbits and thin-disk emission can be directly linked to generalized entropy via the horizon response.

In 2019, the first image of a black hole's shadow based on observation was released by the Event Horizon Telescope Collaboration (EHT). This paper shows that despite the EHT's emphasis on a single image as its final result, there were countless plausible ways of rendering the data, among which researchers could not easily choose. To obtain a single image from the extremely noisy and sparse data, it was necessary to select one of multiple plausible approaches, or to average the results from different approaches, at each stage of data processing. We examine the epistemic and aesthetic choices involved at various stages, and explore what the images would have looked like if the EHT had made different choices. We suggest that the most valuable evidence produced by the EHT comes not from the single image it ultimately advertised as its central result, but from the demonstration of the limited variability that emerged from the specific choices made.

Multiple cosmological observables, such as the galaxy overdensity or cosmic shear, consist of fields sampled at the discrete positions of astrophysical sources. Recent work has presented methods to estimate the angular power spectra of such fields, avoiding the construction of pixelated sky maps and the finite-resolution effects associated with them. In this work, we present a method to estimate the disconnected (also known as "Gaussian") covariance of these angular power spectra, addressing subtle effects such as the effective area overlap between different catalogue-based fields and the additional Poisson-like variance arising from the discrete nature of the catalogues. The method relies on the so-called Narrow-Kernel Approximation to account for the contribution of distinct source pairs to the estimator, while including the noise-like contributions from self-pairs exactly. We explicitly compare this approach with a brute-force method that can produce the exact covariance for sparse samples, and validate it against simulations. We show that the method is accurate in realistic scenarios, spanning both dense and noise-dominated datasets (e.g., cosmic shear) and sparse, noise-dominated observables (e.g., fast radio bursts). The method is implemented in the public code NaMaster.

Loop quantum gravity (LQG) predicts quantum modifications to classical black-hole spacetimes, which may leave imprints on the dynamics and gravitational-wave signals of compact objects in the strong-field regime. In this work, we investigate the orbital dynamics and gravitational-wave signatures of extreme mass-ratio inspirals (EMRIs) in a self-dual loop quantum gravity black hole spacetime. We analyze test-particle motion in the static, spherically symmetric self-dual LQG geometry characterized by two quantum parameters: the polymeric parameter $P$ and the minimal area parameter $a_0$. The effective potential and orbital structure are systematically studied, and we quantify the influence of quantum corrections on circular-orbit stability and strong-field orbital behavior. Compared with the classical Schwarzschild spacetime, LQG corrections modify the near-horizon orbital dynamics. Based on the orbital evolution, we construct gravitational-wave waveforms and investigate the impact of quantum corrections on waveform morphology. We find that LQG effects accumulate during the long inspiral phase, leading to noticeable signal deviations from the classical case. To incorporate rotation, we construct a rotating extension of the self-dual spacetime using the Newman--Janis algorithm. The resulting LQG-corrected Kerr geometry is used to analyze orbital motion, revealing the interplay between spin and quantum corrections in strong-field trajectories. Finally, we perform a Fisher matrix analysis to estimate potential constraints on quantum parameters from future space-based gravitational-wave detectors. Our results indicate that EMRI observations provide a promising avenue to probe quantum gravitational effects in black-hole spacetimes.

During their propagation, ultra-high energy cosmic rays produce cosmogenic photons. The expected flux level of these photons may vary by orders of magnitude depending on parameters such as the spectrum and composition of cosmic rays at injection or the source distance. We investigate the photon yields for various assumptions on injection parameters. The photon yield is largest for proton-emitting sources at about 15 Mpc distance for cosmogenic photons above $10^{18}$ eV. While the photon yield from protons always exceeds the one from heavier nuclei of the same total energy, the differences are reduced for larger source distances. Then, we quantify the cosmogenic photon fluxes for different source scenarios. We regard mixed-composition scenarios that were found to provide a reasonable description of the data from the Pierre Auger Observatory. In addition, benchmark scenarios leading to comparably high ("maximum") or low ("minimum") photon fluxes are determined assuming pure proton or pure iron primaries. For the mixed-composition scenarios that do not contain initial protons, the predicted cosmogenic photon fluxes are below present experimental limits by more than 1.5 orders of magnitude. In case of a substantial fraction of protons at the highest energies, the related photon flux might be in reach. Certain parameter combinations of pure proton scenarios are constrained already by present photon limits.

We study a class of Schwarzschild black holes embedded in an exponential-spheroidal dark matter halo, modelled by a phenomenological density profile $ρ(r)=ρ_0 e^{-r/r_0}$. By solving the Einstein equations for a static, spherically symmetric spacetime, we obtain an analytic solution for the lapse function that reduces to the Schwarzschild spacetime in the absence of the halo and to a regular halo configuration when the central black hole mass vanishes. Indeed, the two halo parameters, $ρ_0$ and $r_0$, describe the strength and radial extent of the dark matter distribution. We analyse the curvature structure, energy conditions, shadow observables, scalar quasi-normal modes and grey-body bounds of the resulting spacetime. The Ricci scalar and the Ricci square remain finite at the origin, whilst the Kretschmann scalar retains the usual central tidal singularity in the presence of a black hole mass. The weak, null, and dominant energy conditions are satisfied, whilst the strong energy condition is violated on a finite radial interval. We also show that the halo monotonically shifts the photon sphere and the shadow radius, which allows us to derive approximate constraints from the EHT observations of M87* and Sgr A*. For scalar perturbations, the Padé-resummed WKB approximation yields stable quasinormal frequencies, while the standard WKB approximation becomes unreliable for higher overtones and strong-halo configurations. Finally, the greybody bounds indicate that the halo weakens transmission through the effective barrier, particularly at low frequencies.

Ultralight bosonic dark matter (UBDM) that couples to electromagnetism can generate an oscillating magnetic-field signal at the Earth's surface. This is referred to as the "Earth transducer" effect, as the Earth converts UBDM into a detectable magnetic field. Similar DM-induced fields in laboratory experiments typically scale with the size $L$ of the experiment. Because the Earth transducer signal instead scales with the large radius of the Earth, $R$, it is one of the most powerful direct probes of UBDM with masses $m_\mathrm{DM}\lesssim1/R\sim3\times10^{-14}\,\mathrm{eV}$. It has many other favorable properties, such as high spatial and temporal coherence and robustness to atmospheric modeling. In this review, we derive the Earth transducer effect and its properties for multiple UBDM models, and discuss current and future prospects to detect it.

We prove a Weyl law for the number of quasinormal modes (QNM) of a Schwarzschild black hole contained in a sector below the real axis. This requires introducing a new pseudodifferential operator calculus tailored to the study of semiclassical spectral problems near threshold energies. Elliptic theory in this calculus can be combined with the method of complex scaling to give uniform resolvent estimates near zero energy for operators that behave at infinity like a semiclassical Schrödinger operator with a repulsive inverse-square potential. Applied to the Regge-Wheeler potential, our methods imply the absence of high angular momentum QNM from a disc whose radius grows linearly with the angular momentum. Together with the asymptotic description of Schwarzschild QNM recently obtained by Hitrik and Zworski, this shows that the number of QNM contained in a small sector below the real axis and with modulus bounded by $λ$ grows as $Cλ^3$. We also study the effect of cutting off the Schwarzschild resolvent away from the event horizon and show that such a cutoff does not lead to any pole cancellations.

We compute the massive particles radial action along hyperboliclike geodesics in various spherically symmetric spacetimes: the standard $4d$ Schwarzschild spacetime, its $d$-dimensional genralization known as Schwarzschild-Tangherlini solutions and for the D3-branes spacetimes, showing useful resummation properties in terms of special (hypergeometric, Fox-Wright) functions in the eikonal limit and generalizing previous results valid for null geodesics. As a consequence, the scattering angle can be resummed too, and we explicitly display the resummed expressions. In addition, in the more interesting situation of a $4d$ Schwarzschild black hole spacetime, following the approach of the quantum Seiberg-Witten curves to the radial equation associated with a massive scalar field, we show that the quantum $a$-cycle (or, equivalently, the \lq\lq renormalized angular momentum") is simply related to radial action also in this massive case, providing fully resummed expressions. Finally, we display the explicit, expanded-form expression of the dual $a_D$-cycle, for which, however, no resummed expressions have been derived yet.

Cosmic filaments are the longest structures in the Universe and the dominant element of the cosmic web, channelling matter onto clusters and shaping the environments in which galaxies form and evolve. Accurate reconstructions of this network across gigaparsec volumes are increasingly important for cosmology and galaxy evolution. However, the most commonly used topological filament finder, DisPerSE, faces a memory bottleneck: it requires a Delaunay tessellation of the full input point set, preventing application to large simulations. Naively splitting the volume fails, as different sub-volumes yield inconsistent tessellations and filament networks. We present a frozen-core method that overcomes this bottleneck while preserving the global topology. The volume is decomposed into overlapping blocks whose tessellations are filtered by a circumsphere criterion retaining only globally valid tetrahedra; a post-processing pipeline merges the tiled outputs through core filtering, deduplication, and boundary stitching. Validation against a monolithic reference on a $300\,h^{-1}\,\mathrm{Mpc}$ MDPL2 subvolume shows 99.6 per cent total length recovery, 100 per cent recovery of density maxima and minima, and 94.7 per cent individual filament matching (the ${\sim}$5 per cent of unmatched filaments are predominantly short, low-significance structures). We apply the method to the full $(1\,h^{-1}\,\mathrm{Gpc})^3$ MDPL2 box (92 million haloes), producing a gigaparsec-scale filament catalogue. As a first application, we measure the connectivity ($κ$) for 22,900 haloes spanning $M_{200\mathrm{c}} = 10^{12}$-$10^{15.5}\,h^{-1}\,\mathrm{M}_\odot$, finding a power-law mass-connectivity relation that extends from group to cluster scales, providing the first confirmation in an $N$-body halo catalogue that the theoretically predicted scaling holds across three decades in halo mass.

For close binaries and star-planet systems, tidal interactions mediate the energy transfer between the orbital motion and the internal flows of the bodies involved, thus playing a central role in their evolution. For equilibrium tides, the associated energy transfer is commonly modeled through an effective viscosity acting on the tidal flow. However, the scaling of viscous dissipation efficiency with tidal frequency $ω_\text{T}$ remains debated, particularly when $ω_\text{T}$ greatly exceeds the convective eddy turnover frequency $ω_\text{c}$. Previous numerical studies have addressed this issue by subjecting a turbulent convective flow to an oscillating background shear mimicking equilibrium tides. In this work, we adopt a novel three-layered convective box -- designed to represent a stellar convection zone sandwiched between two stable layers -- driven by an external periodic forcing. We quantify tidal dissipation efficiency by the forcing power on the flow in steady state. Our results yield a shallower scaling of tidal power per unit mass with $ω_\text{T}$ than reported in earlier shear-flow simulations. This scaling is consistent with the prediction by \cite{Terquem2021}, suggesting that the effective turbulent viscosity depends only weakly on $ω_\text{T}$, although our simulations are restricted to $ω_\text{T}\lesssim 10ω_\text{c}$. Moreover, we find no evidence of inverse energy transfer (or ``negative viscosity''), a phenomenon observed in some prior shear-flow simulations. We further investigate the influence of rotation within the same local framework. Slow rotation ($Ω\lesssim ω_\text{T}$) tends to enhance the tidal power, whereas fast rotation ($Ω\gtrsimω_\text{T}$) significantly suppresses it. We discuss the limitations of our approach and the broader implications of our findings.

We develop an analytic treatment of primordial non-Gaussianity in multifield inflation that is nonperturbative in the constant curvature--isocurvature mixing strength $λ$. Using exact linear solutions for the coupled curvature perturbation $ζ$ and isocurvature perturbation $σ$, we construct dressed propagators and derive exact integral representations for the tree-level bispectra generated by the interactions $\dotζ^2σ$, $\dotζ\,σ^2$, and $σ^3$. This formalism resums curvature--isocurvature transfer to all orders in $λ$ and applies for arbitrary values of the entropy mass $μ$. We obtain closed-form expressions for the leading squeezed limit of the bispectrum contributions and recover the well-known cosmological-collider and quasi-single-field results in the weak-mixing limit. In the strong-mixing regime, where conventional transfer perturbation theory breaks down, we find that both the power spectrum and the bispectrum can be dramatically enhanced, giving rise to distinctive nonperturbative scaling laws for the reduced non-Gaussian amplitude. Together, these results open a new analytic window onto multifield inflation beyond the weak-coupling approximation and establish a framework for studying cosmological-collider signals, primordial-black-hole production, and loop corrections in strongly mixed inflationary dynamics.

Hamiltonian analysis of the first-order Katanaev-Volovich model of two-dimensional gravity with torsion. The first-order action already singles out natural canonical pairs: the auxiliary Lorentz scalars are conjugate to the spatial connection and zweibein. An extended Dirac-Bergmann embedding isolates an auxiliary second-class sector whose elimination recovers the canonical structure encoded in the first-order action and leaves the first-class constraints generating the local gauge symmetries. An independent Faddeev-Jackiw reduction yields the same reduced brackets. The Katanaev/Poisson-Sigma Casimir is then recovered, up to normalization, directly from the reduced Dirac-Bergmann first-class constraint ideal, before imposing any gauge condition. This identifies the Casimir as a global label of the reduced canonical sectors; after the static normalization is chosen, it supplies the Hamiltonian parameter of the torsionful branch. The same normalization is applied to that branch in dilaton gauge, whose field equations are verified on shell. In this static sector the Casimir-normalized radial field does not coincide with the metric Killing norm: the diagonal representative satisfies \(NB=e^{4βr}\). Consequently, torsion modifies the Killing temperature through the normalization of the Killing time, while the horizon entropy retains its standard two-dimensional dilaton value and the Casimir-normalized first law holds.

Context. In recent years, clusters have been observed that host multi-component haloes, both in non-merging and merging systems. The existence of these multi-component haloes suggests that there is no clear distinction between the single components. Aims. Abell 2244 is an intermediate-mass cluster that hosts a double component diffuse radio emission. The aim of this paper is to carry out a in-depth study of the diffuse radio emission to constrain its origin and characterize its main radio properties. Methods. In this work we present LOFAR HBA, MeerKAT UHF, and L-band observations of the cluster Abell 2244. We investigated the nature of the diffuse radio emission, combining high sensitivity radio data with XMM-Newton deep X-ray observations. We also used mock LOFAR observations to investigate contamination of the emission from faint radio sources. Results. We find an integrated spectral index of $α^{1279}_{144} = 0.9 \pm 0.1$ for both components, where only the radio halo shows spectral steepening at higher frequencies. These values are comparable with the spectral indices observed in disturbed massive clusters. The outer component does not follow the same radio X-ray correlation as the radio halo, which suggests a different physical origin. Conclusions. By analysing the physical and morphological properties of the diffuse emission, we find that the characteristics of the outer component of the emission are intermediate between those of radio haloes and of known megahaloes. Hence, we speculate that the source is either a morphologically disturbed radio halo, caused by a minor merger interaction, or a megahalo but we cannot reach a final classification. From the mock observations, we find that it is unlikely that the emission is caused by faint sources at low resolutions.

Pre-main sequence (PMS) early-type stars are rare due to their rapid evolution. Confirming PMS B stars is accordingly valuable for constraining higher mass star formation scenarios. Although the Orion Nebula (ON) region offers an ideal laboratory for such studies, its population of B stars remains poorly characterized. We aim to determine spectral types, masses, and ages of B and early A stars surrounding the ON, to identify robust PMS candidates. We combine optical and near-infrared spectroscopy to estimate spectral types using Brackett, He, Si, and Mg lines. Photometry from Gaia, 2MASS, and WISE is used to construct colour-magnitude diagrams to fit isochrones via chi-square minimisation, yielding stellar ages and masses. Dynamical masses from eclipsing binaries are employed as independent constraints on the mass range allowed for each spectral subtype. We derive stellar ages and masses for 53 stars and spectral classifications for 48 of them, identifying 30 PMS candidates, including some that were previously assigned to luminosity classes I-III. Several stars show spectroscopic variability, potentially linked to circumstellar material or binarity. Our combined spectroscopic and photometric approach identifies robust PMS B-star candidates and provides a validated framework for distinguishing them from evolved counterparts - in this instance, refining the census of early-types young stars in Orion. The age distribution of the PMS candidates offers preliminary clues about the star formation history of the ON region.

We study the reconstruction of conventional cosmic-string signals with LISA in the presence of all major known astrophysical foregrounds expected in the LISA band. These include stellar-origin black-hole binaries (SOBHBs), galactic (WDs) and extragalactic (ExWDs) white dwarfs, extreme-mass-ratio-inspirals (EMRIs), and massive black-hole binaries (MBHBs). Using the Simulation-based Inference package GWBackFinder, we perform a joint inference on the LISA noise, foregrounds, and signal, across a range of injected string tensions $Gμ$. We find that reconstructing tensions with an error $\lesssim 10\%$ requires values as large as $Gμ\gtrsim 10^{-11}$, i.e. a factor $\sim10^5$ larger than previous estimates with no foregrounds, and $\sim 10^2$ larger compared to estimates accounting only for SOBHB and WD foregrounds. This work is the second in a series initiated in Ref. arXiv:2508.05395, which aims to quantify LISA's ability to measure representative cosmic-string models.

This study explores the nonlinear interactions between gravitational waves in an expanding universe. Random ensembles of gravitational waves are evolved numerically in cosmological models whose spatial volumes increase by more than an order of magnitude during these simulations. These evolutions show the spectra of the gravitational waves evolving as energy cascades away from the wavelengths at the peak of the initial spectra toward both longer and shorter wavelengths. Evolutions performed at different gravitational wave amplitudes are shown to produce cascades that scale with amplitude in the way predicted by the four-wave scattering models of gravitational-wave turbulence.

Star clusters are perfectly suited for studying the formation, evolution, and dynamics of stars and their host galaxies. For this, we need to estimate total masses, radii and shapes of star clusters. These parameters strongly influence their fates in the host galaxies. However, there is no agreement about these characteristics in the literature. The published values widely disagree. We estimated total masses and cluster radii using a very conservative approach: calculating member masses and summing them. Furthermore, we investigated the three-dimensional characteristics of open clusters and their limitations. We used a commonly used grid of evolutionary tracks for different photometric sources, including 2MASS, Gaia, and Pan-STARRS. The interpolation method was tested using synthetic clusters built with ASteCA. To estimate three-dimensional shapes, we used the distribution of the well-known Galactic coordinates and inverse parallaxes. We estimated the total masses and radii of about 7000 open clusters and observed traces of tidal tails. Individual values can be used in future $Gaia$ data releases to obtain even more precise values. The current DR3 allows the study of only three-dimensional shapes up to 500 pc. Beyond this distance, we find a significant needle-like shape due to uncertainties in observed parallaxes.

We investigate the thermodynamic topology of charged AdS black holes in a non-commutative spacetime sourced by Lorentzian-smeared matter distributions. Since exact analytical solutions for the critical thermodynamic quantities are not available, we employ a perturbative expansion in the non-commutative parameter and validate the resulting expressions through numerical analysis. Using the generalized off-shell free-energy framework, we explore the topological structure of the thermodynamic phase space and evaluate the corresponding winding number that characterizes the phase transitions. Our results reveal that non-commutative effects introduce qualitative modifications to the thermodynamic behavior compared with the standard Reissner-Nordström AdS black hole. Furthermore, we demonstrate that the bulk and boundary descriptions possess an identical global thermodynamic topology, providing strong evidence for the correspondence between their topological structures. We also investigate the lower bound on the remnant mass implied by the second law of black-hole thermodynamics and observe that non-commutative corrections modify key thermodynamic quantities, with particular emphasis on the entropy and the final black-hole mass.

This work provides a critical reassessment of the cosmological models presented in the article "Non-linear interactions in cosmologies with energy exchange" Eur. Phys. J. C 80, 120 (2020) arXiv:1907.06410 . It points out and corrects several mathematical inconsistencies in the original article. These include a flawed simplification of a Liénard-type equation, unjustified omissions of integration constants, and an incorrect use of the variation-of parameters method. By deriving the exact analytical solutions, it is shown that the corrected mathematical framework fundamentally contradicts the claims of the original article.

We present a class of regular axisymmetric black hole geometries fully characterized by the parameters $\{{\cal M},a\}$ and possessing the Kerr event horizon. This family interpolates between regular spacetimes, configurations with integrable singularities, and the Kerr solution as a limiting case. Its main features are: (i) the existence of quasi-extremal configurations without requiring $a \approx {\cal M}$; and (ii) a possible framework toward an analytical description of Kerr black hole formation from an initially regular configuration.

Stellar multiplicity is key in dynamical evolution of open clusters (OCs) and processes of stellar formation and evolution. Since most stars form in multiple systems, investigating how environmental properties affect their occurrence is crucial. We aim to investigate how binary fraction and mass ratios change across different OC environments. Using a sample of 773 OCs, we identified binary systems and estimated binary fractions, obtaining values in the ranges 0.10-0.85 overall and 0.06-0.79 for high mass-ratio systems. No strong dependence on age or evolutionary stage is found, while an anticorrelation between metallicity and the binary fraction is identified. However, young and old clusters exhibit distinct mass-ratio distributions. We also find that the probability of a star being the primary component increases with stellar mass. In contrast, the probability of a star belonging to a binary system increases with mass for masses below 1 solar mass, and remains between 60% and 70% for high masses. Binary systems are preferentially located in the inner regions of clusters compared to single stars, and the mean mass ratio decreases with increasing distance from the cluster center. These results suggest that the binary fraction appears to be set at early times and remains largely unaffected by cluster dynamical evolution. The concentration of binaries in the inner regions of clusters likely reduces their susceptibility to dynamical escape.

We study cosmological collider signatures in a two-field inflationary system with constant-turn derivative mixing between the canonically normalized curvature fluctuation and a massive isocurvature field. Building on recently derived exact hypergeometric solutions that treat the quadratic mixing nonperturbatively, we construct the mixed propagators constituting the cosmological correlators. A Mellin-Barnes approach helps isolate the pair of nonanalytic late-time branches carried by a heavy field. For a cubic isocurvature self-interaction, these branches contribute towards a squeezed bispectrum with a power-law envelope and logarithmic oscillations. The oscillation frequency encodes the heavy mass, while the amplitude and phase retain the full mixing dependence rather than a perturbative expansion. We perform the squeezed limit integral analytically and compare it with numerical results across representative masses and mixing strengths. At fixed mixing we derive the large-mass JWKB expansion of the squeezed correlator and its phase. We also give integral representations for the isocurvature Wightman function. The research idea was suggested by ARC, the calculation was performed by GPT, and the results were checked by the authors.

Upcoming cosmic microwave background (CMB) and large-scale-structure surveys require theoretical power spectra with numerical errors well below their observational uncertainties over the scales that carry most of the constraining power. We describe a substantial update to CAMB designed to provide fast, high-precision predictions for two key outputs: the lensed CMB and matter power spectra. The central development is a new treatment of the hyperspherical Bessel functions used for line-of-sight integration in non-flat cosmologies. A leading-order Olver construction maps the curved radial equation onto the flat spherical Bessel equation by matching their actions through the turning point. The resulting approximation is exact in the flat limit, remains smooth through the turning point, and reduces near flatness to a simple rescaling of the flat Bessel argument and amplitude. We also describe updated integrators, a recalibrated fast recombination model, stabilized parameterized post-Friedmann dark-energy evolution, and improvements to CMB lensing accuracy. Numerical convergence is assessed by comparing unboosted default results against more converged calculations. The defaults meet conservative $10^{-3}$ pointwise convergence targets over the main lensed-CMB and quasi-linear matter-power ranges relevant for future surveys. Errors measured in typical runs are substantially smaller than this. We also describe the convention dependence of the nominally linear matter power spectrum when a homogeneous calculation attempts to represent the effects of reionization heating. Essentially all of the new algorithms and code were developed with LLMs or AI agents under human supervision.

Bubble-wall friction controls the dynamics of first-order cosmological phase transitions. In Boltzmann-equation approaches, a major uncertainty arises from infrared gauge bosons, whose contribution is artificially enhanced in the massless approximation. We study the impact of thermal masses by including them consistently in both the Liouville operator and the collision integrals. Thermal masses suppress the source term for out-of-equilibrium perturbations while also reducing interaction rates. These effects largely cancel for top quarks, giving only percent-level changes, but they strongly suppress the infrared gauge-boson contribution, shifting the dominant momenta to scales of order the temperature. As a result, gauge bosons become subleading and wall velocities are close to those obtained from top-quark friction alone. We illustrate this in the singlet-extended Standard Model. Our results show that thermal masses reduce the sensitivity of friction calculations to the poorly controlled infrared sector of the plasma.

We establish a local obstruction to continuous Lorentzian extensions at a class of warped spacelike singularities. The criterion is expressed through two integrability conditions, a monotonicity condition on the relative warp factors, and divergence of the longitudinal factor; it does not require any symmetry of the closed fiber. The main geometric step is a radial compression of terminal causal traces, which replaces the rotational deformation available in spherical symmetry. The compression yields a compact chronological separator in an adapted boundary chart. Longitudinal translations then produce radial-slice distances that diverge intrinsically while remaining uniformly controlled in the extension chart. Next, we construct the canonical one-horizon Birmingham-Kottler spacetime in global Kruskal coordinates and classify all finite proper-time ends of its timelike geodesics. Every boundary-approaching finite maximizer supplied by a putative extension is thereby forced to the singular end. The local obstruction and the geodesic classification imply $C^0$-inextendibility for the one-horizon Birmingham-Kottler family with nonpositive cosmological constant and every closed connected fiber satisfying $\text{Ric}_{γ_Σ}=(n-2)kγ_Σ$, without assumptions of homogeneity, orientability, or simple connectivity.

Runaway stars are high-velocity stars ejected from their birth environments that can provide insights into the kinematic history of the stellar cluster they were ejected from. We derived runaway star probabilities for 40 O-type stars and $24,487$ B-type stars taken from a recently published volume-complete sample of OB stars within 1 kpc of the Sun. We fit a Galactic rotation model to the observed proper motions of these stars and identify runaway stars using both a fixed 2D peculiar velocity threshold of $23\,km\,s^{-1}$ and by comparing individual peculiar velocities to the dispersion of the whole sample. We find runaway fractions of $17.5^{+0.1}_{-2.5}\%$ for O-type stars and $6.9\pm0.1\%$ for B-type stars; both using the fixed velocity threshold method. These values are consistent with previous studies, but with differences that are largely attributable to the underlying samples of OB stars used in various studies to identify runaway stars and to variations in the methods used to select them.

We re-examine spontaneous scalarization of black holes within Starobinsky gravity supplemented by the Gauss-Bonnet invariant. A novel feature is uncovered: scalarized solutions split into two smooth branches that connect at a common minimal horizon radius, a multi-branch structure previously unreported for static, spherically symmetric scalarization. Extending the theory with a Maxwell field, we find that this multi-branch structure persists, while a new additional disconnected branch emerges within certain parameter ranges. We thoroughly analyse the transition from a single smooth branch to two disconnected branches. Lastly, we verify, employing the standard Maxwell thermodynamic relations, that all charged hairy solutions obey the first law exactly.

Accurate knowledge of the redshift distributions of unresolved galaxy populations is essential for extracting the cosmological information encoded in the cosmic optical background. We present the first framework for estimating these distributions directly from multi-band maps of unresolved background light, using conditional normalising flows trained on realistic image simulations. For imaging qualities comparable to those expected from the synergy between the Euclid and Rubin LSST surveys, our model achieves sub-per cent accuracy in both the mean and standard deviation of the flux-weighted redshift distributions when the training and target samples are statistically well matched. Furthermore, the network proves highly resilient to incomplete photometric coverage when combined with tailored data imputation strategies. To address the challenge of statistical mismatches between simulations and real observations, we propose incorporating observational quantities into the target variables, providing a built-in diagnostic to assess model reliability and uncertainty from the predictions themselves. We also demonstrate the feasibility of map-based tomographic analyses, showing that the model retains sufficient pixel-level detail to recover redshift distributions for tomographically defined subsamples with near sub-per cent accuracy across all bins. These results establish conditional normalising flows as a viable tool for redshift estimation of unresolved sources, opening new opportunities for component separation, signal interpretation, and cosmological inference using multi-band optical background fluctuations.

We present an infrared, millimetre, and radio survey of 20 Class 0-III young stellar objects in the Ophiuchus A L1688 star-forming cluster, combining high-resolution (7-25 au) VLA and JWST observations with archival ALMA data. We implement physically motivated models to derive dust and ionised gas properties, spectral behaviour and their relative contributions through the millimetre-centimetre radio spectral energy distribution. Our models reveal circumstellar dust disks that are, on average, tens to hundreds of times more massive than millimetre-only estimates (subject to uncertainties arising from the choice of dust opacity) and contain millimetre-sized grains even at the Class 0 stage. Owing to the VLA's high resolution we are able to connect outflows to their origins, detecting protostellar jet emission on scales of 10s-1000s au. Our results represent a homogeneous characterisation of the dust and ionised gas properties in Ophiuchus and present a potential solution to the long-standing 'missing disk mass' problem. However, our understanding is still limited by resolution and sensitivity at frequencies <40 GHz. Future facilities like the SKA and ngVLA are needed to provide the necessary capabilities to fully spatially resolve this emission (<0.18") even in one of the closest star-forming regions.

The distribution of heavy elements in stars is described using a phenomenological approach, in which Lagrange parameters related to temperature and the chemical potentials of protons and neutrons are introduced within a freeze-out concept. Slope parameters are considered which describe the gross behavior of the distribution of the heavy elements. Universality and deviations from universality are discussed, and various examples are provided. These slope parameters may be of interest for characterizing the conditions under which heavy elements form, but the astrophysical sites where heavy elements are produced remain to be determined.

James Webb Space Telescope (JWST) has discovered unexpectedly bright, rapidly growing galaxies in the early universe, which were not predicted by most previously existing galaxy formation models. Using synthetic JWST observations of the Azahar simulation suite, we show that comprehensive non-thermal physics ("Full-Physics") produces compact, self-regulated galaxies that match observations from $z = 12$ to $z = 3$. This model also produces broad surface brightness distributions, where the bright end is dominated by compact sizes and bursty star formation. This compact starburst scenario naturally explains the detection of bright $z > 10$ galaxies in flux-limited surveys. By contrast, a model with standard hydrodynamics yields systems that are smaller and more concentrated than current data, while a model with calibrated supernova feedback produces unphysically large systems nearly twice the size of those observed. At lower masses ($\mathrm{M}_{*} < 10^{8}\,\mathrm{M}_{\odot}$), the Full-Physics model predicts sizes that are smaller than can be resolved with JWST, consistent with extrapolations from observations of higher-mass systems. Future observations with higher resolution could resolve this population and elucidate the physics driving the formation of the first galaxies.

We introduce a geometric framework that organizes the second-order statistics of the Elasser fields into polarization states on generalized Poincaré spheres. In this representation, energy, cross-helicity, residual energy, and the phase lag between counter-propagating wave packets emerge as complementary polarization parameters. We derive a Bloch-analogue equation governing the evolution of polarization states and show that distinct polarization geometries are associated with different cascade dynamics. The framework predicts that transitions in the turbulent spectral scaling coincide with changes in the polarization state of the interacting modes.

Neutral regions of the intergalactic medium (IGM) during the Epoch of Reionization (EoR) remain largely unexplored due to the limitations of existing probes. Owing to discoveries of numerous high-redshift radio-bright sources, the 21-cm forest, a series of absorption features imprinted by the neutral IGM in the spectra of such sources, now offers an attractive probe of the thermal and ionization state of the predominantly neutral IGM at $z\gtrsim5.5$. We analyse archival upgraded Giant Metrewave Radio Telescope (uGMRT) observations of J352-15, the brightest known radio-loud quasar in the EoR ($z=5.82$), to measure the one-dimensional (1D) power spectrum of the 21-cm forest. By comparing the observed power spectrum with forward-modelled synthetic spectra generated from cosmological simulations spanning a wide range of ionization and X-ray pre-heating scenarios, we perform Bayesian inference even in the absence of a statistical detection. We also present an independent Murchison Widefield Array measurement, although its lower sensitivity prevents competitive constraints. Using uGMRT, we achieve a sensitivity of $3.62\,\rm mJy\,beam^{-1}$ per $6.1\,\rm kHz$ channel. While we do not detect the 21-cm forest statistically, the null detection jointly constrains the mean neutral hydrogen fraction, $\langle x_{\rm HI}\rangle$, and the mean temperature of the neutral IGM, $\langle T_{\rm HI}\rangle$. At the $68\%$ credible level, our analysis disfavours cold and substantially neutral IGM models at $z\approx5.6$, including models with $\langle T_{\rm HI}\rangle \lesssim 27\,\rm K$ for $\langle x_{\rm HI}\rangle=0.1$. These limits probe parameter space allowed by existing Ly$α$ and 21-cm observations, indicating substantial pre-heating of the neutral IGM above the adiabatic cooling floor. This demonstrates that the 21-cm forest has entered the regime of observationally informative statistics.

We show that a regular solution for primordial tensor fluctuations can arise from the higher-order multipoles of the collisionless neutrino distribution after neutrino decoupling. Focusing on the leading case with the neutrino octupole mode (tensor-octupole mode), we derive the initial conditions for the Einstein-Boltzmann system and calculate angular power spectra for the cosmic microwave background (CMB) anisotropies. Compared with the standard gravitational-wave mode, the tensor-octupole mode has a weaker large-scale metric response. It therefore gives a suppressed reionization bump and a different oscillation phase in the tensor CMB power spectra, providing a way to separate it from the standard tensor mode.

We present the design of DUET, a dual-channel imager being built for the SPECULOOS-Southern Observatory (SSO) to detect and characterise transiting terrestrial exoplanets orbiting ultra-cool dwarfs. A dichroic beamsplitter at 955\,nm directs visible light to a deeply-depleted silicon CCD and near-infrared light to a CMOS-based InGaAs detector, enabling fully simultaneous photometry with bandpasses from 0.4 to 1.7\,\textmu m. The near-infrared filters have been chosen to suppress sensitivity to atmospheric precipitable water vapour (PWV) variability, a dominant source of correlated noise in ground-based infrared photometry of cool stars. We describe the optical and mechanical architecture, the dichroic and filter selection, the choice of detectors, and the control system.

In this work, we investigate the violation of the chaos bound for spinning test particles in Gauss-Bonnet anti-de Sitter spacetime, focusing on the regulatory roles of the Gauss-Bonnet parameter and spacetime dimensionality. In five-dimensional space time, the Lyapunov exponent grows monotonically with particle spin. In contrast, in eight- and nine-dimensional spacetimes, it exhibits non-monotonic behavior-first decreasing and then increasing-reflecting the nonlinear nature of higher-dimensional tensor couplings. The Gauss-Bonnet parameter significantly modulates the violation by reshaping the near-horizon geometry: in five dimensions, the deviation of the Lyapunov exponent from the surface gravity first increases and then decreases with the Gauss-Bonnet parameter, whereas in the higher dimensions the bound is more easily violated. Increasing the total angular momentum of the particle also enhances chaos; however, when the Gauss-Bonnet parameter and black hole charge are small, the spacetime dimensionality, rather than the angular momentum, dominates. These results establish the spacetime dimensionality and the Gauss-Bonnet parameter as important factors governing the validity of the chaos bound in modified gravity theories.

In the last decades, spacetime noncommutativity and the associated deformations of relativistic symmetries have attracted a lot of interest, as several phenomenological windows into quantum gravity are approaching genuine Planck-scale sensitivity. However, the physical significance of the mathematical structures introduced to deal with spacetime noncommutativity is still debated, and some crucial pieces are missing or poorly understood. From time to time it has been suggested that valuable insight into these conceptual challenges could come from the analysis of appropriately designed first-quantized toy models, in which major technical and interpretive issues can be effectively managed or sidestepped altogether. In this paper we take seriously this suggestion and develop the first fully consistent and fully relativistic first-quantized model of two particles propagating and interacting on a noncommutative spacetime. The specific spacetime noncommutativity implemented in our model, which we call 'time-commutative $κ$-plane', had already been proposed as a suitable arena for a first-quantized analysis, but previous studies were mostly heuristic and failed to provide a full description of the deformed relativistic symmetries. We here go much beyond those pioneering attempts: we find a full characterization of the appropriate deformed Poincaré symmetry algebra as well as its Galilean limit; we build a single-particle quantum model carrying an irreducible representation of the deformed Galilei algebra; we exhibit two consistent, Galilean-relativistic descriptions of a system of two quantum particles interacting via a deformed harmonic potential, finding that the structure of the two-particle symmetry generators is intimately connected with the deformation of the interaction law.

We investigate the Casimir effect for a massive real scalar field confined between two perfectly reflecting parallel plates in the presence of a position-dependent effective mass, a mechanism for coupling a scalar background to a scalar field. Exact normal modes are obtained by solving the corresponding Klein-Gordon equation, leading to a transverse energy spectrum that exhibits a characteristic Landau-like structure despite the absence of an external magnetic field. Upon quantization of the field, the vacuum energy is evaluated by means of generalized zeta-function regularization together with an appropriate renormalization procedure. The renormalized vacuum energy naturally separates into a Landau-like contribution and an additional term induced by the spatial dependence of the effective mass. We show analytically and numerically that both contributions are exponentially suppressed in the strong-coupling regime. In the opposite limit, the Landau-like contribution smoothly reproduces the standard vacuum energy for a massive scalar field confined between parallel plates, whereas the additional contribution becomes singular owing to the restricted domain of validity of the exact spectrum. Except in the vicinity of this singular limit, the vacuum energy is shown to be dominated by the Landau-like sector. Our results establish a direct connection between position-dependent effective masses and boundary-induced quantum vacuum phenomena, providing a new exactly solvable framework for the investigation of Casimir effects in spatially inhomogeneous relativistic systems.

Building on our previous study, which demonstrated the importance of accounting for departures from local thermodynamic equilibrium (LTE) in elemental-abundance determinations and of using asteroseismic ages, we investigate spatial variations in the empirical [Y/Mg]-age relation across the Galactic disc using a substantially larger stellar sample. We analysed high-resolution stellar spectra and determined Mg and Y abundances through spectral synthesis of multiple spectral features, rigorously accounting for non-LTE (NLTE) effects. We derived asteroseismic ages for stars exhibiting solar-type oscillations and used cross-checked isochrone-based methods for the remaining stars. We determined atmospheric parameters and Mg and Y abundances for 528 Galactic field stars, together with asteroseismic ages for 307 stars and isochronal ages for 221 stars. We also identified two new triple-lined and nine double-lined spectroscopic systems. Combining the present sample with that of our previous study yielded a total of 736 stars, which we used to examine the [Y/Mg]-age relation across the Galactic disc. The relation shows systematic spatial variations that likely reflect differences in star-formation and chemical-enrichment histories. In general, [Y/Mg] tends to increase with metallicity over the investigated age range. At supersolar metallicity, however, this trend may weaken, and the [Y/Mg]-age relations become flatter than those of solar-metallicity stars, which show lower [Y/Mg] values at young ages and higher values at old ages.

An observer which propagates in a spacetime with dynamical gravity has access to an algebra of observables which is expected to be a von Neumann algebra with a trace. The observer can use projections from the algebra to perform local measurements. By using this fact we construct a simplicial complex out of measurements recorded on the worldline of the observer and we propose that such a complex captures topological information about spacetime, even when this is fluctuating.

We present angular correlation and power spectral analyses of the clustering of VST ATLAS galaxies, LRGs and QSOs and their cross-correlations with the ACT DR6 CMB lensing map with its $\approx3\times$ higher resolution than Planck DR3. We first use $Λ$CDM Halofit models at linear scales to estimate galaxy, LRG and QSO bias, $b$, from the ratio of the 3-D power spectra, $b= P_{gg}/P_{gK}$ and hence the mass clustering amplitudes, $σ_8$. For galaxies we find $b_G(z=0.15)=1.22\pm0.07$, $σ_8(z=0)=0.71\pm0.06$ and for LRGs $b_{LRG}(z=0.26)=2.76\pm0.11$, $σ_8(z=0)=0.63\pm0.15$, both consistent with $Λ$CDM predictions. But for QSOs, we estimate a bias of $b_Q(z=1.7)=4.44\pm0.24$ and $σ_8(z=0)=0.49\pm0.06$, the latter significantly lower than expected for $Λ$CDM and leads to an observed $0.15<z<1.7$ gravitational growth rate faster than predicted for $Λ$CDM. At smaller non-linear scales, HOD model fits imply a broad halo mass distribution for $z\approx0.15$ galaxies but much narrower mass distributions for LRGs and QSOs. More surprisingly, the HOD fit for QSOs implies $M_{eff}=5\times10^{14}M_\odot$, $\approx10\times$ higher than expected. Finally, while the LRG and QSO HOD models fit $w_{gg}$ and $w_{gK}$ consistently, the same is not true for the $z\approx0.15$ galaxies unless we hypothesise anti-bias with $b_G\approx0.55$. This result supports previous QSO lensing analyses that also found anti-bias at $r<5$h$^{-1}$Mpc. We suggest that while HOD + NFW halo models may well describe LRG mass profiles and clustering, at intermediate scales the dominant galaxy population (and QSOs) may follow the alternative hierarchical clustering model of \cite{Peebles1974} where galaxies trace the mass more closely than in a halo model.

The total dust mass of protoplanetary disks is a key property that determines the potential for planet formation. Upper Scorpius (USco), with an age of ~5-12Myr, provides an important laboratory for investigating the evolution of dust reservoirs on timescales comparable to those of planet formation. In this work, we analyze the dust mass distribution of 136 full and transitional disks in USco using the largest ALMA 0.88mm continuum sample currently available for the region. To improve the accuracy of dust mass estimates, we construct a grid of 918 self-consistent radiative transfer models that account for stellar-mass-dependent disk sizes, accretion rates, and porous dust properties. The models yield a new calibration between dust temperature and stellar luminosity, predicting systematically higher dust temperatures for low-mass stars than commonly adopted prescriptions. Using these revised dust temperatures together with porous dust opacities, we derive dust masses for the USco disks and compare them with those of a younger sample in the Chamaeleon~I star-forming region. We find a median dust mass of 0.95M_E for the USco disks, approximately six times lower than that of the Chamaeleon I disks (5.69M_E), providing strong evidence for substantial depletion of millimeter-sized dust grains over the first several Myr of disk evolution. We confirm the previous finding of a highly significant correlation between stellar mass and dust mass, with a slightly steeper relation in USco than in Chamaeleon I. The low dust masses observed in USco, together with their comparison to mature exoplanetary systems, suggest that a large fraction of the primordial solid reservoir has already been incorporated into larger bodies, removed by radial drift, or hidden from millimeter observations by ages of 5-12 Myr.

I present a study for double-line spectroscopic binaries content in spectra from the RAVE spectra, using composite spectral model. Three complementing selections found 2813 composite spectra, belonging to 2605 unique targets. Also these results were compared with automatic classification based on t-SNE map, which shows good agreement. Additionally I identified several spectra affected by problems with wavelength calibration.

Stellar multiplicity alters the density structure of protoplanetary discs and thereby the initial conditions for planet formation. Yet, the interplay between companion-disc interactions and dust growth remains poorly understood. The goal of this work is to investigate to what extent the density structure of a disc undergoing tidal interactions with a companion star promotes or inhibits the growth of dust grains. We perform a set of hydrodynamical simulations of protoplanetary discs orbiting one or both stars of a binary, including dust growth and fragmentation. We explore a range of companion orbits and compare the results with a single-star reference case. We find that dust growth is mainly driven by local accumulations of dust. In circumbinary discs, the maximum grain size is up to five times smaller than in isolated discs. This result likely originates from the perturbations caused by the inner binary, which prevent dust grains from properly settling and drifting. As a consequence, the conditions required to trigger strong clumping driven by the streaming instability are difficult to achieve. In contrast, circumstellar discs in binary systems exhibit grain sizes similar to those in isolated discs, leading to comparable conditions for strong clumping by the streaming instability. Planet formation through core accretion seems challenging in circumbinary discs harbouring binaries larger than a few au, suggesting that circumbinary planets observed near the dynamical stability limit did not form in situ. Conversely, perturbations from external companions only marginally affect density-driven dust growth compared to isolated systems.

We propose a hybrid realization of Starobinsky inflation in which the inflationary epoch ends through vacuum decay. The model consists of an effective two-field system with a metastable Starobinsky branch shifted with respect to the true one. During the observable stage, the inflaton slow-rolls along the false branch, until a first-order phase transition in an orthogonal direction connects it to the true branch and ends inflation abruptly. This old-inflation-like exit skips the last part of the would-be Starobinsky trajectory. As a result, the Cosmic Microwave Background pivot scale exits the Hubble radius further from the minimum of the false branch than in ordinary Starobinsky inflation, raising the scalar spectral tilt $n_s$ while preserving the characteristic small tensor-to-scalar ratio. This provides a simple way of moving Starobinsky inflation towards the high-$n_s$ region favoured by recent ACT-related combinations. The same vacuum transition leaves a stochastic gravitational-wave relic whose peak frequency is controlled by the tunnelling timescale and the subsequent reheating history.

The Paradox of the Third Particle arises when particles are described relative to one of them serving as a reference frame. Although it is typically attributed to quantum superpositions, we show that the paradox and its ramifications$\unicode{x2014}$such as the relativity of subsystems$\unicode{x2014}$already occur classically. In light of this insight, we establish a no-go theorem that holds whenever physical subsystems, whether classical or quantum, are used as reference frames: if one demands that frame transformations be information-preserving, then it is impossible to meaningfully partition the world into subsystems, like individual particles, from the perspective of each frame.

Large-scale structure provides a powerful probe of inflationary physics through primordial non-Gaussianity (PNG): the galaxy power spectrum depends on local PNG through scale-dependent bias, while the galaxy bispectrum depends sensitively on both equilateral and orthogonal PNG. In this paper, we study whether galaxy surveys can also probe folded PNG, whose shape is enhanced near $k_1+k_2-k_3\rightarrow0$. We consider three inflationary models with folded PNG, including excited initial states, imaginary speeds of sound, and dissipative inflation. These models fall into two classes: cutoff-regulated cases in which the folded-enhanced region has a power-law width, and dissipation-regulated cases in which the enhanced region is exponentially narrow. We develop a numerical pipeline for computing the corresponding PNG contributions to the redshift-space galaxy power spectrum multipoles and bispectrum monopole within the EFTofLSS. Using Fisher forecasts, we show that most of the constraining power on folded PNG comes from the galaxy bispectrum. For the cutoff-regulated models, nuisance parameter marginalization causes only a mild loss of information at large folded enhancement, but finite Fourier-space binning degrades constraints once the folded region becomes narrower than the bin width. For the dissipation-regulated models, the exponentially narrow folded enhancement is hard to resolve and the observable signal instead comes from the broader support of the template, leading to weaker binning dependence but larger overlap with the equilateral template. Our results show that folded PNG is a distinctive and promising target for galaxy bispectrum analyses, and the detectability depends on the width and morphology of the folded enhancement. The numerical pipeline developed in this work is general and can be used to study a wide class of non-separable primordial bispectra.