高能暂现源 · 每日文献综述

Gravitational-wave observations of compact-binary inspirals offer the opportunity to test deviations from general relativity in both strong and weak-field regimes. In previous work, we developed a theory-independent formalism for describing compact-binary dynamics in metric theories of gravity without preferred frames, using the parametrised post-Newtonian (PPN) couplings together with an additional set of scalar sensitivity parameters that encode violations of the strong equivalence principle. Here, we extend this framework to include preferred-frame effects, of the type that can arise in (for example) vector-tensor theories of gravity. This is achieved by introducing a time-like vector field that identifies the preferred frame, and then by allowing compact body masses to depend on the invariant formed from this field and the body's four-velocity. We calculate the modified equation of motion up to first post-Newtonian order (1PN), where the preferred-frame PPN parameters $α_1$ and $α_2$ acquire contributions from our new vector sensitivities. We further combine scalar and vector sensitivities in a unified formalism, which we validate with an example scalar-vector-tensor theory. This approach provides the orbital dynamics required to extend gravitational-wave constraints on PPN and sensitivity parameters to theories of gravity that admit preferred frames, as well as those that do not.

We investigate the gravitational wave (GW) signatures of compact binaries embedded in extended dark matter (DM) configurations in hydrostatic equilibrium. If a neutron star is surrounded by a sufficiently massive and extended envelope, an inspiraling companion experiences dynamical friction (DF) in addition to the standard GW energy loss. We show that this environmental effect can be isolated through a GW observable, the $D$-function, which directly characterizes the additional dissipative power induced by the surrounding medium. Since the density of the envelope is directly determined by the DM equation of state together with the stellar boundary conditions, the frequency dependence of the $D$-function provides direct information about the macroscopic properties of the dark sector. We develop a regression-based framework to reconstruct both the density profile and the DM equation of state over the density range probed by observations of the GW inspiral. Using representative DM models as benchmarks, we demonstrate that the method accurately recovers the input equation of state while remaining largely independent of the microscopic realization of DM. Our results show that future GW observations of compact binaries can provide a probe of the equation of state of DM.

Luminous red novae (LRNe) are astronomical transients arising from unstable mass transfer and common envelope phases in close binary systems, culminating in stellar mergers. Their cold, expanding ejecta provide the ideal conditions for molecule and dust formation. We investigate the late-time dust and molecular evolution of the LRN M101 OT2015-1, a high-mass LRN progenitor ($18\pm 1$M$_\odot$), using multi-band near-infrared (NIR) and mid-infrared (MIR) observations spanning up to ~5 years post-outburst. Archival and unpublished photometry from NEOWISE, Spitzer, Keck NIRC2 and MOSFIRE, are interpolated via 2D Gaussian process regression. Spectral energy distributions (SEDs) are modelled with 1D spherical radiative transfer models to track the evolution of dust mass, dust temperature, and central source properties. At +150d post-peak, the SED is well-fit by a pure stellar blackbody ($T_{\rm eff}=3330$K) with negligible dust (log$M_{\rm dust}/$M$_\odot<-6.36$). Rapid dust condensation begins around day +200 ($T_{\rm dust}=1591$K), with dust mass increasing to log$M_{\rm dust}/$M$_\odot =-3.65$ and optical depth reaching $τ_V =64$ by +1300d. A prominent NIR re-brightening at ~600d ($M_K=-12.04$), accompanied by a dust reheating bump ($T_{\rm dust}=1567$K), highlights a second phase of dust nucleation likely driven by shock interactions. Low-resolution NIR MOSFIRE spectra are analysed for line identification and also using an LTE isothermal slab model to characterise CO molecular features. The MOSFIRE spectra reveal an O-rich environment with photospheric expansion velocities of ~$430-530$km s$^{-1}$, as measured in the Pa$β$ emission line, and high CO column densities (log$N_{\rm CO}$/cm$^{-2}=20.9$ and $20.7$ at +142d and +197d, respectively). These results confirm that LRNe from massive progenitors are prolific producers of cosmic dust and are efficient molecular factories.

Gravitational-wave observations can reveal sources whose signals are not known in advance. Searches that do not require a predicted waveform are therefore an important complement to searches for specific source classes. For the Laser Interferometer Space Antenna (LISA), the challenge is to find such signals among overlapping astrophysical sources and disturbances in the instrument. We present \texttt{cWB-space}, which identifies candidate signals by following how their power is distributed in time and frequency, and then reconstructs parts of their waveforms without imposing a source model. Simulations of merging massive black holes, other burst signals, and instrumental disturbances test both candidate identification and the information carried by the detector's response. The response comparison estimates its background from the observed data. Tests of disturbances in several laser measurements examine where a similar response can arise from an instrumental origin. Searching the Sangria simulated LISA data, we recover all six injected massive-black-hole binaries as the six highest-ranked candidates. Their reconstructed waveforms agree well with the injected signals over the intervals studied. The results demonstrate another route to investigating transients, while leaving the rate of false detections and general discrimination of instrumental disturbances to future validation.

Recent simulations suggest that heavy seed black holes may form in weakly metal-enriched atomic cooling halos, where the supermassive-star progenitor and small-scale stellar fragments emerge nearly coevally. In this picture, the newly born heavy seed is naturally embedded in a metal-enriched Pop~I/II nuclear star cluster rather than in an isolated pristine environment. We investigate whether disk-induced tidal disruption events (TDEs) from these Pop~I/II stars can provide an efficient and sustained growth channel for heavy seed black holes. We construct a semi-analytical model for stellar orbital damping, disk capture, migration, and tidal disruption around a heavy seed black hole, and incorporate the resulting disk-induced TDE contribution into cosmological merger trees with baryonic and metallicity evolution. Heavy seed host halos are selected from atomic cooling halos with $Z\lesssim10^{-3}Z_\odot$ that satisfy either a rapid gas-inflow criterion or a strong Lyman--Werner radiation criterion. We find that disk-induced Pop~I/II TDEs can dominate the early growth of heavy seeds: the median black hole mass grows from $\sim10^4\,M_\odot$ to $\sim10^5\,M_\odot$ within the first $\sim0.1$ Gyr after seed formation, and reaches several $10^5\,M_\odot$ by $\sim0.2$ Gyr. The cumulative mass supplied by TDEs initially exceeds that from gas accretion and remains comparable over the first $\sim200$ Myr. Including disk-induced TDEs shifts the black hole population toward higher masses, increases the abundance of massive black holes at $z\sim9$--10, and produces larger black hole-to-stellar mass ratios. This channel helps alleviate, but does not fully remove, the tension between heavy-seed models and the most extreme high-redshift black hole candidates, suggesting that additional growth mechanisms may still be required.

We perform high-resolution 2.5D single-fluid magnetohydrodynamic (MHD) simulations to explore the development of cool-dense structures within plasmoids during chromospheric magnetic reconnection. The model incorporates temperature-dependent ionization degrees of hydrogen and helium, resulting in improved diffusivities and viscosity, as well as adequate radiative cooling. The numerical results show that plasma is significantly hot with temperatures reaching several tens of thousands of Kelvin in newly developed plasmoids in the low initial plasma-$β$ cases, $β_0$ = 0.05. Later, the localized accumulation of plasma and decreasing temperature result in an explosive much stronger radiative cooling process. Radiative cooling peaks over the temperature range 8000 K$-$20,000 K. The co-spatial density enhancement, substantial radiative cooling, shorter radiative cooling timescales, and a significant temperature decrease support the existence of thermal-instability-like condensation within the plasmoids. Similar cool-dense structures are identified in all low-$β_0$ cases at different chromospheric altitudes, suggesting that this occurrence is not limited to a single chromospheric layer. In contrast, in the high initial plasma-$β$, $β_0$ = 0.5 case, the maximum temperature inside the dense plasmoids is only about 8000 K. Therefore, the radiative cooling has never entered into the explosive increasing stage and the thermal-instability-like condensation does not happen. These findings reveal that plasmoid-trapped condensation may develop in chromospheric reconnection once radiative losses become self-amplifying under low-$β_0$ conditions.

Large primordial curvature perturbations not only produce primordial black holes (PBHs) but also inevitably source a scalar-induced stochastic gravitational-wave background upon horizon reentry. We analyze the combined LIGO--Virgo--KAGRA O1--O4a data to constrain two representative inflationary mechanisms for generating such perturbations: ultra-slow-roll inflation and an inflationary phase transition. Detecting no evidence for either scenario, we place 95% credible upper limits on the curvature-spectrum amplitude across the frequency range accessible to ground-based interferometers. Translated into the PBH context, these limits already exceed conventional constraints, probing abundance fractions far below unity. Our results remain robust even when the PBHs themselves are too rare to be directly detected or have evaporated. This work demonstrates that stochastic gravitational-wave observations offer a powerful and complementary probe of small-scale inflationary physics and PBH formation, with upcoming interferometers promising to extend sensitivity to a wider range of inflationary epochs and PBH masses.

We assess whether electromagnetically identified supermassive black hole (SMBH) binary candidates populate the rare, high-amplitude tail of the gravitational wave (GW) amplitude distribution. Using an SMBH binary population model fitted to the NANOGrav 15-year data, we find that 3C~66B and Mrk~501 are likely to stand out from the GW background, making them promising targets for individual-source searches. Furthermore, we show that individual detections can probe the binary hardening mechanism, as models with strong environmental hardening predict a higher abundance of individually resolvable binaries than purely GW-driven models. Applying the same population fits and accounting for the confusion noise from the unresolved population, we forecast that the Square Kilometre Array Observatory (SKAO) will resolve tens of individual binaries, with 3C~66B robustly detectable.

Many dark sector models predict the formation of dark objects, such as solitons and dark stars, which can be searched for through their gravitational lensing of gravitational waves (GWs). Although these objects vary widely in size and compactness, most GW lensing studies have focused on point-like lenses. The finite size of an extended lens is important when it exceeds its Einstein radius. We evaluate the frequency-dependent effects on GW waveforms from extended lenses and demonstrate that they can be probed with current and future GW data. While finite-size effects can weaken the bounds on the fraction of dark matter in these objects compared to the point-like limit, current GW data provides complementary constraints to other gravitational tests for lens masses between $10^2M_\odot$ and $10^5M_\odot$; future LIGO-Virgo-KAGRA data and next-generation observatories will surpass their sensitivity. As expected, we find that the finite-size effects are important when the lens radius exceeds $\sim \text{few} \times 10^{6}R_\odot (M_L/100 M_\odot)^{1/2}$. Interpreting these constraints within specific models (a simple dissipative dark sector and axion stars), we show that current and future observations probe significant portions of the microphysical parameter space.

At low redshift, scatter in the Type Ia supernova (SN Ia) Hubble diagram is increased by peculiar velocities (PVs) and correlations between SN distances and their host-galaxy environments, limiting the precision of cosmological distance measurements. We investigate these effects using 1086 spectroscopically-confirmed SNe Ia from the Type Ia Supernova Trove from ATLAS in the Nearby Universe (TITAN) sample in the redshift range $0.01<z<0.05$. We identify 314 group-associated SNe, including 80 SN "cousins" occurring in different galaxies within 32 common groups. We first examine whether using the group-averaged redshifts of SNe in galaxy groups can mitigate PV-induced scatter; however, we find that the Hubble residual scatter increases slightly from $0.184^{+0.017}_{-0.009}$ mag using individual host-galaxy redshifts to $0.200^{+0.016}_{-0.015}$ mag using group-averaged redshifts. For the sample of SN cousins, we next analyze pairwise differences in their distances and compare their scatter to the Hubble residual scatter of the full SN sample. For analysis variants that limit line-of-sight differences in distance modulus between cousins, we find $\sim$30-40% lower scatter from SN cousins at significances of 2.3-2.8$σ$. We also find tentative evidence that these differences in scatter may be driven by the youngest groups, with a 2$σ$ reduction in scatter for groups with high fractions of spiral galaxies. These results suggest that SN cousins may provide a novel route for increasing SN Ia distance precision and understanding the role of host-galaxy and group properties on SN Ia distance measurements.

Ideal-GRMHD calculations provide the bulk accretion flows used in black-hole emission models. A localized dissipation prescription can add a resolved map of current-sheet activity while retaining that dynamical reference. We implement such a prescription in Athena++, using a smooth threshold on the dimensionless current proxy $α_J$ to select the magnetic-diffusion coefficient. The constrained-transport update is coupled to a conservative energy-flux correction. Gas heating follows from primitive recovery; $q_{Ohm}=ηJ^2$ is recorded as a diagnostic, without a second energy source. Static Fourier and traveling Alfvén tests measure the evolved thermal gain, and an open-boundary Schwarzschild test closes the Killing-energy ledger. The relative total-energy residual is below $2\times10^{-15}$ in these tests. A two-resolution Harris matrix gives localized rate exponents $0.510\pm0.027$ and $0.488\pm0.028$, consistent with $1/2$ over the specified early interval. The $η=10^{-3}$ rate exceeds the same-resolution ideal control by a factor of 5.96. In matched axisymmetric M87*-like runs, localized diffusion changes the early mean magnetic flux, accretion rate, and normalized flux by less than $0.02\%$, with a radial-density distance of $0.005\%$. During the late active phase, a common-restart on/off comparison keeps these mean shifts below $1.6\%$, within the intrinsic temporal variability, and gives a density distance of $0.29\%$. Uniform diffusion at the tested coefficient reduces the raw flux and accretion rate by $85\%$ and $99.8\%$. These comparisons establish a spatially selective diffusion prescription with explicit energy accounting and a quantified, small bulk-flow response.

Superoutbursts and superhumps are characteristic signatures of SU UMa-type cataclysmic variables, yet the full diversity of superhump evolutionary behaviour remains poorly constrained owing to the limitations of ground-based photometric monitoring. Here we report a systematic analysis of 30 SU UMa-type dwarf novae observed with the Transiting Exoplanet Survey Satellite, covering 37 superoutburst events. We detect coherent superhump signals in 29 systems-including five first-time detections-and determine or refine orbital periods for 13 objects. The high-cadence light curves clearly resolve the canonical three-stage (A-B-C) superhump period evolution. Using Stage A periods, we derive dynamical mass ratios for 18 systems, consistent with established cataclysmic variable evolutionary tracks. The measured Stage B period derivatives match the range of values from ground-based campaigns, with prominent positive drifts concentrated in short-period, low-mass-ratio systems. Repeated superoutbursts yield consistent evolutionary patterns, demonstrating that superhump morphology is an intrinsic, repeatable property. Two systems break the standard template: RZ LMi shows an inverted stage sequence inconsistent with classical precession theory, while ASASSN-14kj exhibits no stage evolution but a coherent long-period modulation. Persistent superhumps during normal outbursts in three systems provide direct evidence that eccentric disk structures can survive beyond their parent superoutbursts, revealing a decoupling between thermal accretion and tidal eccentricity cycles. These results demonstrate the power of space-borne photometry for probing accretion disk dynamics and testing precession models across the cataclysmic variable parameter space.

In this manuscript, we investigate the shadow and polarization images of a Simpson-Visser rotating black hole surrounded by a ballistic approximation accretion flow model. Solving the numerically geodesic and radiative transfer equations, we discuss the influence of the regularization parameter $g$, spin parameter $a$, and observer inclination angle $θ_o$ on the resulting images at $230\,\mathrm{GHz}$ with an infalling motion. The results interpret that, a bright circular ring corresponding to higher-order images is observed, accompanied by an inner region of decreased intensity. Both $g$ and $a$ has little influence on the size of the higher-order images, but significantly changes their shape and intensity distribution. Whereas, variation in $θ_o$ modify the image morphology, producing a crescent-shaped bright region on the left side. Finally, the polarization patterns trace the brightness distribution and vary with both $g$ and $a$, reflecting the spacetime structure. These results demonstrates that the intensity and polarization in thick disk models provide probes of Simpson-Visser rotating black holes and near-horizon accretion physics.

We present the first experimentally measured oscillator strengths for Ni II 3d$^8$4d - 3d$^8$4p transitions. High-resolution Fourier transform spectra were recorded of Ni-He hollow cathode lamps, and intensity calibrated using deuterium standard lamps to determine relative intensities of Ni II emission lines between 200 and 395 nm. Branching fractions were determined for observed lines from 35 3d$^8$4d upper levels in total, and account for at least 95% of the predicted transition probability for 31 of these levels, with sufficient completeness to give reliable branching fractions. Combining our measured branching fractions with four experimental and 27 theoretically calculated energy level lifetimes provided absolute oscillator strengths for 174 lines, for which no previous experimental values exist. We compare the results with three sets of previously published theoretical calculations, illustrating the improvement of laboratory measurements for these atomic data. Please note: The transition probability datasets are withheld from this pre-print to ensure that only the peer-reviewed, definitive versions are released. This approach prevents the propagation of duplicate or inconsistent data across widely used atomic databases and modelling frameworks.

An analysis of 36 hours of data from a DALI haloscope reveals no statistically significant excess attributable to dark-photon dark matter. We therefore set new constraints in the 6.88691--6.91792 GHz band, reaching a dark-photon-to-photon kinetic mixing strength of $χ\lesssim 6.8\times10^{-14}$ at $28.54 \, μ\mathrm{eV}$. To our knowledge, this result established the strongest laboratory-based exclusion limit in this frequency range.

DALI is an axion haloscope consisting of a magnetized phased array backed by a conducting mirror and coupled in the near field to a semi-open Fabry--Pérot resonator. The applied static magnetic field makes both the dielectric interfaces and the conducting mirror sensitive to axion-induced electromagnetic conversion. Each interface acts as a radiating surface, and the resulting fields are projected onto the mode collected by the resonator and delivered to the receiver. We derive the detected power in terms of the power available from the magnetized mirror, the coherent contribution of the dielectric interfaces, the transverse mode overlap, the loaded quality factor, and the receiver-coupling coefficient. This formulation separates two distinct enhancement mechanisms. The dielectric-interface emissions may add coherently, producing a dielectric boost, while the semi-open Fabry--Pérot resonator provides enhancement through resonant storage of the coupled electromagnetic field. These contributions depend differently on the dielectric thicknesses, spacings, and resonant mode, and should therefore be evaluated independently. The same assembly can operate between the limits of a coherently boosted dielectric haloscope and a mirror-sourced, resonantly enhanced Fabry--Pérot haloscope. This combined architecture offers a flexible approach to resonant axion searches at frequencies for which conventional closed microwave cavities become increasingly limited in conversion volume.

The study of massive stars in binary and higher-multiplicity systems that participate in particle acceleration is a key topic at the crossroads of massive star physics, shock physics, and galactic cosmic ray astrophysics. From an observational perspective, radio measurements are our pri- mary tool for identifying these systems through their synchrotron radio emission. Out of the 54 such systems known to date, all but two have been discovered via their non-thermal radio emission. However, identifying these systems is not straightforward. The main challenge lies in free-free absorption, which can obscure the synchrotron signature and hinder detection. This paper summarizes recent developments in our understanding of these systems, with a particular focus on the strong observational bias introduced by free-free absorption. This bias significantly limits our ability to determine the true fraction of particle accelerators among colliding-wind binaries.

We study the thermodynamics of Lorentzian Taub--NUT spacetimes in Einstein--Gauss--Bonnet AdS gravity in arbitrary even dimensions, constructed as $U(1)$ fibrations over Einstein--Kähler base manifolds. We compute the temperature from the surface gravity and the energy as the conserved charge associated with the stationary Killing vector using the off-shell Abbott--Deser--Tekin formalism. Within the same framework, we obtain the entropy as a horizon Noether charge. The result agrees with the Iyer--Wald formula and includes a Gauss--Bonnet correction to the Bekenstein--Hawking area law. Retaining the Misner strings whenever present, we formulate a first law of full cohomogeneity in which the NUT parameter varies independently of the horizon radius. This requires an additional thermodynamic charge and its conjugate potential, which we determine explicitly. We also briefly discuss the static limit.

Self-interactions between dark matter (DM) particles facilitate the inter-particle redistribution of energy within the central region of DM halos. Recent studies of dark matter spikes around massive black holes, and the diversity in rotation curves of dark matter rich low-mass galaxies motivate the exploration of self-interaction cross-section $\mathcal{O}(10)\,\rm cm^2/gm$. At such high scattering rates, DM can lead to the formation of supermassive black hole seeds, through the gravothermal collapse of halo cores, under certain cosmological conditions. Quasars near cosmic dawn are powerful probes for examining the formation scenario of high redshift supermassive black holes, and their connection to structure formation. In this work we point out the favorable initial cosmological conditions that are likely to provide the black hole seeds resulting in supermassive black holes, mediated by core-collapse in self-interacting dark matter halos. Employing a semi-analytic prescription of core formation, and realistic mass accretion and halo merger histories, we compare the existing observations of high-redshift supermassive black holes with those predicted for our core-collapse framework. We find the median values of velocity-dependent self-interacting dark matter parameter space $σ/m_χ\sim 56\, \rm cm^2/gm$, and $ω=101\,\rm km/s$, assuming an Eddington accretion rate of unity. Sub-leading values are also presented for sub and super-Eddington accretion rates. We also report the derived self-interacting dark matter model parameters to account for the observed binned supermassive black hole mass functions at high-redshifts.

We present an extended study of the gravitationally localized soliton-like solutions to the minimally-coupled Einstein-Dirac-Higgs equations, embedded in asymptotically Minkowski spacetimes. The equations of motion describing these Yukawa-coupled Dirac stars are generalized to any even number of constituent fermions. We first expand the discussion of two-fermion ground-state solutions initially analyzed in Leith et al. [Phys. Rev. D. 107, 106020 (2023)]. Upon extending our analysis to excited states and many-fermion states, we find that both exhibit different behaviors to their two-fermion ground-state counterparts. In these excited states and many-fermion states, the Higgs field may exhibit stepwise increases and at times decrease within the soliton, which has not been seen for the two-fermion ground states. We also propose the potential cause of a significant degree of ADM-to-fermion mass disparity, which is present in states with strong Yukawa-coupling.

We study the dynamical scalar tidal Love numbers of wormholes that provide viable mimickers for black holes, focusing on thin-shell Schwarzschild and Damour-Solodukhin geometries. Using a matched near- and far-zone expansion, we determine their tidal response in the low-frequency regime. The presence of a long throat introduces an additional characteristic scale and naturally separates the modes into two classes. Super-throat modes probe the global wormhole geometry and are sensitive to both asymptotic regions, whereas sub-throat modes probe only one side of the wormhole and effectively perceive the throat as a black-hole horizon. We derive the scalar tidal Love numbers analytically for both classes of modes and show that their dissipative parts exhibit distinct low-frequency behavior, reflecting whether one or both potential barriers participate in the scattering process. We further find that, as the wormhole approaches the black-hole limit, the super-throat contribution becomes progressively negligible, while the sub-throat response smoothly reduces to that of a Schwarzschild black hole. These results demonstrate that the tidal response of wormholes depends crucially on whether the perturbation probes the global structure of the throat.

We present a fully nonlinear relativistic description of the observed pulsar timing modulations, defined through the ratio of the proper-time intervals between two successive emissions of radio pulses and their observations by a pulsar timing array. Working in the limit of a vanishing emission interval, we derive the observed pulsar timing modulation to second order in relativistic perturbation theory around a Minkowski background, without fixing a gauge and retaining the full scalar, vector, and tensor content of the metric perturbations. Although the derivation naturally introduces several gauge-dependent intermediate quantities, we explicitly demonstrate that they combine into a coordinate-independent expression. Moreover, we explicitly show that the second-order timing modulation from two neighboring radio pulses coincides with the observed redshift, defined as the fractional change in wavelength along a single geodesic. The agreement represents a nontrivial second-order realization of the exact nonlinear equivalence proven in Magi & Yoo 2026.

We report an independent identification of the ultra metal-poor (UMP) star ($\rm[Fe/H] =-4.06$) $Gaia$ DR3 $\texttt{source_id}$ 4795913112968206720 (GDR3_479591) in the $Gaia$ mission's Blue and Red Photometer 'XP' spectro-photometric catalog. We combine multi-band photometry, astrometry, and high-resolution spectroscopy to confirm GDR3_479591 as a red giant-branch (RGB) star located at ${\sim} 6\,{\rm kpc}$ from the Sun. Abundance analysis under local thermodynamic equilibrium reveals significant enhancements, relative to the solar level, in carbon ($\rm[C/Fe] = +1.54$, after evolutionary correction for depletion in the RGB), nitrogen ($\rm[N/Fe] = +2.64$), and oxygen ($\rm[O/Fe] = +2.62$). The CNO-enhanced GDR3_479591 is thus one of only 5 UMP stars with a detected oxygen abundance. The CNO excess is accompanied by enhancements in several other light elements, such as Na, Mg, Al, and Si. We demonstrate that the chemical pattern of GDR3_479591 can be reproduced by the yields of a single Population~III 'faint' supernova with progenitor mass of $\sim$21-to-28$\,M_\odot$ and a low explosion energy of ($0.3 \leq E_{\rm SN}/(10^{51}\,{\rm erg}) \leq 0.9$). Additionally, we use literature metal-poor stars to show that, contrary to recent propositions for high-redshift galaxies, a mild enhancement in [C/O] does not automatically translate to the high [C/Fe] typically observed in UMP stars in the Milky Way and its satellites. GDR3_479591 could not be dynamically associated with any of the most relevant accreted substructures in the Galactic halo, and we speculate that it was formed in an ultra-faint dwarf galaxy environment that later merged with the Milky Way.

In this study, we present the full (97.3\% complete) 0.8--12.5 $μ$m spectral energy distribution (SED) of an L/T transition object, CWISE J210640.16+250729.0 (CW2106), using the James Webb Space Telescope (JWST). We provide a full characterization of the host star's elemental abundances and age. We empirically derive the bolometric luminosity ($L_{\rm bol}\approx-4.825$ $\textup{L}_\odot$) of CW2106, and obtain estimates of its mass (M$\approx50-62$ M$_{\rm Jup}$), radius (R$\approx0.83-0.87$ R$_{\rm Jup}$), effective temperature ($T_{\rm eff}$$\approx1213$ K), and surface gravity ($\log~g$$\approx5.28$ dex). We find the near-infrared (near-IR) spectrum ($0.8-2.5 ~μ$m) is best reproduced with cloudy atmospheric models while the mid-infrared (mid-IR) spectrum ($5-12.5 ~μ$m) is best reproduced with cloudless models. This suggests a cloud layer restricted to only the deepest observable parts of the atmosphere and is qualified by the lack of a 9 $μ$m silicate feature. Making use of the Mg/Si ratio of the primary, alongside thermochemical models, we predict the clouds in CW2106 to be composed primarily of enstatite (MgSiO$_3$), removing $\sim23\%$ of the bulk oxygen out of the atmosphere. Future retrieval studies will be able to help investigate the existence and full impact of these cloud species.

We present theoretical estimations of the event rates for the interaction between a right-handed fermionic dark matter with an electron bound to a xenon atom. Motivated by recent astrophysical and cosmological constraints on a fermionic dark matter candidate in the sub-MeV mass range, we study such an interaction through an effective electromagnetic channel where the output consists of standard-model particles. This mechanism allows right-handed neutral dark matter fermions to couple with standard-model particles with the interchange of $W^{\pm}$ or $Z$ bosons, without the need to add extra fields. We generalize and extend previous results on this type of channels, by including for the ionization form factor arising from the interaction of the fermionic candidate with bound electrons. In addition, we compute the sensitivity curves for different direct detection experiments in such a challenging light particle mass range.

We construct the first-law-consistent entropy of a geometrically minimal-length-deformed Schwarzschild spacetime, obtained via the areal-radius substitution $R(r)=\sqrt{r^{2}+\ell^{2}}$ on $r\in[0,+\infty)$ with $f(R)=1-2M/R$, whose nonvanishing Einstein tensor sources an effective geometric fluid with no classical matter counterpart. Integrating the first law gives $S=π[r_{h}R_{h}+\ell^{2}\ln((r_{h}+R_{h})/\ell)]$. This coincides in functional form with the semiclassical term found independently by Joshi and Joshi, but we fix its boundary condition $S(r_h=0)=0$ on independent physical grounds and adopt it, rather than the Bekenstein--Hawking area law, as the complete entropy of the model, building the free energy, geometrothermodynamics, and mode-stability analysis on it. Evaporation, governed by the Helmholtz free energy $F(M)$, terminates at $M_{\min}=\ell/2$ in a previously unrecognised endpoint: a degenerate extremal regular black hole, where the regular centre coincides with a degenerate Killing horizon of quadratic order, $f\approx r^{2}/(2\ell^{2})$, at areal radius $\ell$, with $T_{H}\to 0$, $S\to 0$, $C\to 0^{+}$, and finite curvature everywhere; we display its Penrose--Carter structure for the first time. The same entropy, with $\ell$, defines the equilibrium state space of a Legendre-invariant geometrothermodynamic (GTD) description whose curvature scalar diverges independently at the Davies-type transition $M^{*}=\ell/\sqrt{2}$ and at $M_{\min}$, a divergence with no counterpart in the minimal-length black hole literature, specific to a genuine horizon at $S=0$. We embed this remnant within the observational discriminant noted qualitatively by Tsukamoto: exact shadow degeneracy combined with a measurable photon-ring flux enhancement $r_{n}=e^{-2π/a}>e^{-2π}$, accessible to next-generation very-long-baseline interferometry.

The longitudinal evolution of second-harmonic anisotropy inherited from the first interaction in extensive air showers is investigated with CORSIKA simulations. Events with large initial anisotropy are selected. Second-harmonic observables are evaluated separately using the coordinate and momentum azimuths at several atmospheric depths and compared with their corresponding initial harmonic orientations. More than 84% of the initial second-harmonic signal is attenuated within the first 20 g cm$^{-2}$ of shower development. In coordinate space, the second-harmonic correlation with the initial orientation persists to ground level at approximately 0.09% of its initial magnitude. This residual is evaluated against a matched source-isotropized reference, constructed for each selected event by independently randomizing the azimuths of the first-interaction final-state particles and simulating the shower under identical atmospheric conditions. The positive coordinate-space ensemble-mean difference at ground level is statistically resolved, and the two samples show little event-level separation. In momentum space, a weak ensemble-level residual remains at 200 g cm$^{-2}$, and the original and source-isotropized signals become statistically indistinguishable by 300 g cm$^{-2}$ and remain so at ground level.

We construct a classical formulation of gravity in terms of the vierbein that makes the Hilbert action polynomial in gravitational perturbations and identify some matter models that admit a polynomial coupling to such perturbations as well. We introduce the density vierbein variables that factorize the inverse metric density while retaining an explicit local Lorentz frame. With the introduction of a new auxiliary field, one can construct an action that is polynomial in such variables and their perturbations. Constructed the BRST complex for the model and derived propagators and interaction rules. In four dimensions, a scalar field with the canonical kinetic term and a potential admits a finite number of coupling terms with the density vierbein perturbations. Among all Horndeski gravity models, only a narrow subclass admits a polynomial coupling to the density vierbein perturbations. For instance, the Einstein--scalar--Gauss--Bonnet model always has an infinite tower of interactions with the density vierbein perturbation. Similarly, the standard kinetic term for the Dirac fermions and the standard kinetic term for a vector field both admit an infinite tower of interactions. Consequently, the density vierbein variables provide a great simplification for scalar-gravitational couplings, but the simplification is not strong enough to produce a realistic model with a finite number of matter-gravity terms.

We present XMST, an extended minimum spanning tree framework for identifying spatially coherent stellar structures using an objective, data-driven fracture-scale criterion. XMST combines percolation analysis with Jenks Natural Breaks optimisation, restricting the MST edge-length distribution to the subcritical regime before determining the final fracture scale. The method was validated using 1000 controlled Monte Carlo realisations containing eight empirical stellar-association templates, including a deliberately overlapping pair. The Percolation-Jenks fracture scale was highly reproducible, with a median of 17.028 pc and a between-realisation standard deviation of 0.066 pc. The injected structures were recovered with a mean completeness of 0.9996 and mean purity of 0.7413, while alternative CDF and Mean Edge criteria selected substantially larger fracture scales and produced markedly lower purities. Propagation of the published distance uncertainties through 10,000 additional XMST reconstructions produced a median absolute fracture-scale change of only 0.282 pc. Under these perturbations, mean completeness was 0.8605 and mean purity 0.7126, while 99.30 per cent of injected-template cases continued to satisfy the adopted detection criterion. Individual membership was less stable, with peripheral and locally sparse members showing lower persistence than structural cores. The deliberately overlapping pair was resolved spatially in only 15 of 1000 realisations; a reddening-based post-processing diagnostic increased this to 446, although with a corresponding completeness-purity trade-off. XMST therefore provides a robust method for identifying candidate stellar structures and their stable cores, while detailed outer membership and strongly overlapping populations require additional astrophysical information.

We study the implications of a recent measurement of the primordial helium fraction from the Large Binocular Telescope for cosmological inference from the cosmic microwave background. We show that LBT establishes the robustness of cosmological parameters to theoretical assumptions about big bang nucleosynthesis: its empirical calibration of the helium fraction enables constraints on cosmology and inflation that are agnostic to BBN but as precise as those that instead enforce standard BBN predictions. Future CMB surveys require at most a marginal improvement in precision over LBT to maximize their BBN-agnostic constraining power when the radiation density is free (and no more than a factor of two improvement across all cases we consider). We then apply the LBT measurement to a number of scenarios that feature new physics in BBN and the CMB. First, we constrain nonstandard radiation sectors (interacting and free-streaming) and search for evolution of the radiation abundance between nucleosynthesis and recombination. We then test models that alleviate the Hubble tension and the tension between CMB and baryon acoustic oscillation data, including self-interacting light relics and varying fundamental constants; LBT precludes most but not all of the models we consider via their effect on BBN. Finally, we use the LBT measurement as an indirect but independent test of the neutron lifetime anomaly, inferring values that are consistent with "bottle" experiments and $2.4 σ$ below "beam" experiments.

Einstein gravity in four asymptotically flat dimensions is governed by a tower of soft theorems obeying an $\mathcal{L}w_{1+\infty}$ commutator algebra. This algebra is deformed to $\mathcal{L}_Λw_{1+\infty}$ in the conformally related AdS$_4$ and dS$_4$ spacetimes. Here we construct the larger ``conformal $w$-algebra", denoted $\mathcal{C}w_{1+\infty}$, which acts on conformal gravity in all of these spacetimes. It includes $\mathcal{L}w_{1+\infty}$, $\mathcal{L}_Λw_{1+\infty}$ and the $\mathfrak{so}(4,2)$ 4D conformal algebra as subalgebras. We show that $\mathcal{C}w_{1+\infty}$ is the conformal completion of either $\mathcal{L}w_{1+\infty}$ or $\mathcal{L}_Λw_{1+\infty}$. A derivation of $\mathcal{C}w_{1+\infty}$ is given as the symmetry of the twistor action of self-dual conformal gravity.

We report a 216-hr upgraded Giant Metrewave Radio Telescope (GMRT) Band-4 $550-850$ MHz observation of the COSMOS field, using 7 GMRT pointings to cover an area of $2.4$ sq. deg., with on-source times of $67$ hrs in the central pointing, and $89$ hrs distributed across the other six pointings. We stacked, at a spatial resolution of 90 kpc, the HI 21 cm emission signals from 8,122 star-forming galaxies with accurate spectroscopic redshifts and lying within the FWHM of the GMRT primary beam at their redshifted HI 21 cm frequencies. We detect the stacked HI 21 cm signal from the 8,122 galaxies at $4.2σ$ significance, obtaining an average HI mass of $\langle{M_{\scriptsize{\textrm{HI}}}}\rangle=(15.5\pm3.7)\times10^9 \textrm{M}_\odot$. This is only the second galaxy population at $z\approx1$ with a measurement of the average HI content; the other being the blue star-forming galaxies in the DEEP2 fields. We also detected the median 1.4 GHz radio continuum emission signal from the 8,122 galaxies by stacking the GMRT 680 MHz continuum images, obtaining a weighted-median star-formation rate (SFR) of ${8.90\pm0.92}~M_\odot$ yr$^{-1}$. We measure a characteristic HI-to-stellar mass ratio of $\langle{M_{\scriptsize{\textrm{HI}}}}\rangle/\langle{M_\star}\rangle=(1.15\pm0.27)$ and a characteristic HI depletion timescale of $\langle{M_{\scriptsize{\textrm{HI}}}}\rangle/\textrm{SFR}=(1.74\pm0.45)$ Gyr for star-forming galaxies at $\langle{z}\rangle=1.081$ in COSMOS, both consistent with earlier measurements for the blue, star-forming DEEP2 galaxies at $z\approx1$. Our results support the evidence from the DEEP2 survey that the observed decline in the SFR density at $z<1$ is due to insufficient accretion of atomic gas from the intergalactic medium to replenish the gas reservoir consumed in the process of star-formation.

The treatment of convection is one of the largest remaining uncertainties in models of low mass stars. The Mixing Length Theory (MLT) for super-adiabatic convection has come under particular scrutiny. Evidence is mounting that a single value of the mixing length parameter ($α_\mathrm{MLT}$) should not be applied universally across stellar model grids, although simulations and asteroseismic calibrations disagree on how it should vary with stellar parameters. A variable $α_\mathrm{MLT}$ causes critical systematic changes to the ages of low mass stars, the key age tracers for galactic and exoplanetary studies. In this work we use classical (non-seismic) geometric radii and specialized MIST isochrones with a variable $α_\mathrm{MLT}$ to measure mixing length in detached eclipsing binaries (DEBs) and interferometrically resolved stars, finding plenty of evidence for non-solar $α_\mathrm{MLT}$. In particular we find that standard evolutionary models overpredict the radii of metal-poor interferometric stars and that a sub-solar $α_\mathrm{MLT}$/$α_{\mathrm{MLT},\odot}\sim0.50-0.75$ can neatly explain this discrepancy, consistent with other empirical calibrations and in stark contrast to simulations. We infer low convective efficiency in cool, rapidly rotating lower main-sequence stars, consistent with the known phenomenon of magnetically-induced radius inflation. We also identify several slowly rotating DEBs whose measurements cannot be reproduced by standard isochrones, and we propose these systems as useful case studies of non-solar mixing length in stars outside of the Sun. However, we find no definitive population level correlations between $α_\mathrm{MLT}$ and stellar parameters among the DEBs, calling into question the existence of a ubiquitous mixing length calibration in low mass stars.

Star formation activity in the central molecular zone (CMZ) directly manifests itself as radio continuum free-free emission (Bremsstrahlung) and radio recombination line emission from H II regions surrounding newly formed massive stars. We derive the overall distribution of the H II regions and their fundamental properties: electron temperature (<inline-formula><tex-math id="TM0001" notation="LaTeX">$T_{\rm e}$</tex-math></inline-formula>) and emission measure (EM), and hence electron density in the form of two-dimensional distribution maps over the CMZ by analyzing the ACES (ALMA CMZ Exploration Survey) H40<inline-formula><tex-math id="TM0002" notation="LaTeX">$\alpha$</tex-math></inline-formula> (99.02 GHz) recombination line and 99.6 GHz continuum emission data with synthesized beam widths of <inline-formula><tex-math id="TM0003" notation="LaTeX">$2{_{.}^{\prime\prime}} 45$</tex-math></inline-formula> (0.097 pc at 8.2 kpc) and <inline-formula><tex-math id="TM0004" notation="LaTeX">$2{_{.}^{\prime\prime}} 14$</tex-math></inline-formula>, respectively. We apply the "TeEM" method (<inline-formula><tex-math id="TM0005" notation="LaTeX">$T_{\rm e}$</tex-math></inline-formula>-EM mapping), which creates <inline-formula><tex-math id="TM0006" notation="LaTeX">$T_{\rm e}$</tex-math></inline-formula> and EM maps from input 2D maps of the continuum and integrated line intensity. The analysis covers the entire ACES field from <inline-formula><tex-math id="TM0007" notation="LaTeX">$l\sim -{0{_{.}^{\circ}}6}$</tex-math></inline-formula> to <inline-formula><tex-math id="TM0008" notation="LaTeX">${+0.^{\!\!\circ}8}$</tex-math></inline-formula> and from <inline-formula><tex-math id="TM0009" notation="LaTeX">$b\sim -0.^{\!\!\circ} 2$</tex-math></inline-formula> to <inline-formula><tex-math id="TM0010" notation="LaTeX">$+0.^{\!\!\circ} 1$</tex-math></inline-formula>. The area analyzed is complete and includes previously known H II regions such as Sgr B2, Sgr B1, the Sickle, the Pistol, thermal filaments (Bridges), Sgr A H II regions, the Minispiral, and many other known H II regions. Sgr C is not included in the analysis due to the insufficient signal-to-noise ratio in the recombination line map. The mean electron temperature over the CMZ is determined to be <inline-formula><tex-math id="TM0011" notation="LaTeX">$\langle T_{\rm e} \rangle _{\rm CMZ}= 5872 \pm 78 ~{\rm (SE)} ~\pm 3682~{\rm (SD)}$</tex-math></inline-formula> K (SE: standard error of the mean, SD: pixel-to-pixel standard deviation). Some H II regions, such as Sgr B2 Main and the Minispiral, exhibit large scatter and an internal <inline-formula><tex-math id="TM0012" notation="LaTeX">$T_{\rm e}$</tex-math></inline-formula> gradient of several thousand K per parsec. The EM distribution is more diverse, varying by orders of magnitude from <inline-formula><tex-math id="TM0013" notation="LaTeX">${\sim }10^5$</tex-math></inline-formula> to <inline-formula><tex-math id="TM0014" notation="LaTeX">${\sim }3\times 10^8$</tex-math></inline-formula> pc cm<inline-formula><tex-math id="TM0015" notation="LaTeX">$^{-6}$</tex-math></inline-formula> within the CMZ, as well as within individual H II regions.

Magnetic fields play a crucial role in regulating the collapse of dense molecular clouds, shaping the early stages of protostellar evolution. We present polarization observations in submillimeter wavelengths with the SCUBA-2/POL-2 instrument on James Clerk Maxwell Telescope toward the Class 0 protostellar system L1527 IRS (IRAS 04368+2557). The magnetic field morphology varies across the core of L1527 IRS. Magnetic fields in the eastern region are perpendicular to the outflow axis, while those in the western region show a pinched morphology, overall aligned with the outflow cavity. These distinct bipolar outflow regions also have a clear color difference in near infrared observed by James Webb Space Telescope. In addition, the spectral index derived from 450 μm and 850 μm observations reveals that the northwestern region of the protostellar system is colder and denser compared to the southeastern region. Furthermore, in the large-scale structures and magnetic fields revealed by Herschel and Planck, we find a ~0.1 pc scale filamentary structure parallel to the large-scale magnetic fields in the eastern region and a relatively isotropic mass distribution in the western region. Based on these results, we propose an accretion scenario of the protostellar system in which an asymmetric mass distribution causes the distinct features observed in near-infrared and submillimeter wavelengths.

From its birth, celestial mechanics has been deeply intertwined with the question of the Solar System's dynamical stability. For the inner planets, this question is now statistically settled: Mercury's orbit carries a $\sim$1% chance of destabilization before the Sun leaves the main sequence. The outer Solar System has seemed more secure, with its intrinsic dynamical lifetime estimated at $\sim10^{18}$ years. Even accounting for the Sun's mass loss and stellar flybys, the orbital architecture of the giant planets had been expected to persist for $\sim$100 Gyr. Here we show that these estimates rest on the assumption that solar mass loss is smooth. The recently measured white dwarf recoil demands asymmetric mass loss that is most readily attributed to discrete, independently directed ejections that impulsively perturb stellar motion. As the Sun sheds its envelope in such parcels, the planets' orbits random-walk with amplitude set by the mass-loss granularity. At a coarseness corresponding to observationally permitted kicks, this stochastic forcing restructures the outer Solar System concurrently with the Sun's death. In particular, our numerical experiments reveal that orbit crossings can commence on the red giant branch, with $\sim$40% of realizations undergoing disruption or violent scattering before the white dwarf forms and $\sim$90% self-destructing within 3 Gyr. The outer Solar System's dynamical lifetime thus collapses from $10^{18}$ years to approximately a gigayear after white dwarf formation.

Accelerating black holes in General Relativity are described by the C-metric. We study how this geometry is modified by higher-derivative corrections, focusing on cubic curvature terms of even and odd parity. Using a suitable metric ansatz, we obtain closed-form solutions at first order in the coupling constants. The corrected geometries contain new integration constants, which correspond to physical deformations of the C-metric, and exhibit different behavior depending on the parity of the correction. In particular, parity-violating terms generate an off-diagonal metric component and induce rotation. For AdS solutions, we analyze the thermodynamics, including the Hawking temperature, entropy, and string tensions, and discuss the subtleties in defining the mass and thermodynamic string lengths.

Born-Infeld New Massive Gravity (BINMG) is an all-order curvature extension of New Massive Gravity in three dimensions, whose linearized spectrum around its unique maximally symmetric vacuum contains the two polarizations of a massive spin-two field. Whether an additional scalar degree of freedom appears in the full nonlinear theory has remained an open question. We perform a nonlinear canonical analysis of BINMG using its auxiliary-metric formulation. On the regular branch connected to the maximally symmetric vacuum, the Dirac algorithm yields three first-class diffeomorphism constraints and a second-class pair of scalar constraints. The resulting count gives exactly two local degrees of freedom per spatial point. Thus, nonlinear BINMG propagates no additional Boulware-Deser-type scalar mode on this branch.

We present the results of a driven, ideal magnetohydrodynamics simulation of a molecular cloud to study the formation of filamentary structures in molecular clouds and their fragmentation into dense cloud cores. Shock compression results in the formation of sub-parsec long filamentary structures. Large-scale supersonic flows push these small filaments together and form massive filamentary clouds. The main filament that forms stretches across the full 4.4 pc length of the simulation and has a median FWHM of 0.075 pc, similar to that observed in many molecular clouds. Subfilaments inside the main filament have a median FWHM of 0.03-0.04 pc, similar to the ``fibers" observed in molecular lines. The collision and merger of subcritical subfilaments is an important mechanism for the formation of prestellar cores. Colliding subfilaments and the resulting core at their intersection is a hub-filament system similar to that associated with massive star formation, but on a smaller scale. Core mergers can be significant in the growth of pre-stellar cores and may play a role in the formation of binary stars.

Recent orthodoxy, which we call Curvature Fundamentalism, posits that the field strength $F$ on spacetime exhausts the physically significant content of electromagnetism, at least on prosaic (contractible) spacetimes. We argue that it is gauge invariance that constrains physical significance. As a result, there are physically significant quantities that $F$ does not capture, even on contractible spacetimes. We show that this result is robust: in the presence of charged matter fields, there are interference experiments whose outcome cannot be predicted by $F$ or any other point-local gauge invariant quantities on the basis of initial Cauchy data. We prove this using the example of relative phase of a Klein-Gordon-Maxwell field, and use it to identify a context in which the widely-claimed equivalence between the Maxwell-Faraday formulation $EM_1$ and the gauge formulation $EM_2$ of electromagnetism is untenable, and that new strategies may be needed for the reductionist project.

We propose a framework for understanding the information loss paradox in the context of canonical quantum gravity. We first revisit several approaches to black hole evaporation that do not involve an event horizon. In these models, we assume that each time slice corresponds to a coherent state in the gravitational phase space. Due to this property, the quantum state associated with a given spatial configuration will have a nonzero overlap with another spatial configuration. We show how this property can account for both semi-classical dynamics and unitary time evolution. We introduce an explicit toy model that follows semi-classical time evolution at the coarse-grained level; in addition, its time evolution is unitary at the fine-grained level. The only price that one must pay is the violation of the entropy bound; we discuss reasons why this may be justifiable.

We study the Einstein-Vlasov system near the Schwarzschild spacetime in spherical symmetry. In particular, we consider the case when the matter is supported on bounded geodesics. In this regime, the decay of the matter is driven by phase mixing rather than dispersion. For the linearized problem, we obtain quantitative phase mixing; the key new ingredient proved here is a monotonicity property of the period function. For the nonlinear coupled problem, we prove phase mixing up to the timescale expected from the nonlinear echo mechanism; this is achieved by analysis on dynamical action angle variables and the integral estimates with the vector field method. This construction is made possible by our gauge choice, an isotropic coordinate system together with a foliation of prescribed mean curvature, in which the Einstein equations gain derivatives over the matter due to its elliptic nature.

Bouncing cosmological models replace the big bang singularity with a regular bounce, but face a well-known obstacle: the anisotropic shear grows as a^(-6) during contraction, where a is the average expansion factor, threatening to dominate before a homogeneous, isotropic universe can emerge from the bounce. A standard remedy is a scalar field with an ekpyrotic-like potential that turns negative near the bounce, pushing its effective equation of state above unity so it outgrows the shear. Here we examine how this mechanism affects the subsequent inflationary phase within mLQC-II, a modified loop quantum cosmology (LQC) model in which inflation is otherwise generic. Taking a potential combining ekpyrotic and inflationary components, we numerically evolve the dynamical equations across the bounce for various parameter choices. We find that while some choices of the free parameters of the theory allow the ekpyrotic potential to dominate near the bounce and resolve the shear problem, it substantially reshapes the post-bounce evolution. In particular, parameter choices that yield sufficient inflation without the ekpyrotic mechanism now often fail to do so. Sufficiently long inflation remains possible but appears to require fine-tuning. As our results are numerical, a more systematic analysis will be needed to establish their generality.

We analyze the presence of X-ray surface brightness (SB) discontinuities, such as shocks and cold fronts, in the intracluster medium (ICM) of the 116 galaxy clusters from the CHEX-MATE sample. These features arise from accretion-related processes, including the merging of subclumps onto the main cluster halo and the sloshing of cold gas in a higher-entropy environment. We identify these structures in the XMM CHEX-MATE maps by examining both the SB residuals, obtained by subtracting a cluster model from the observations, and the gradient variations across X-ray images. We validate our method with an extensive analysis and comparison of the discontinuities described already in the literature. Our analysis reveals 66 discontinuities, 32 of which are newly detected, in 48 objects ($\sim$41%). We find that discontinuities in relaxed systems tend to be closer to the core, weaker, and less aligned with the global X-ray morphology compared to those in disturbed systems. Using wavelet-based temperature maps, we provide a preliminary classification of these discontinuities, proposing the occurrence of 8 putative shocks and 34 cold fronts. Furthermore, about 48% of the systems with extended radio emission show evidence of ICM discontinuities; conversely, $\sim$88% of the objects with detected discontinuities have an associated diffuse radio emission. This work also explores the limitations of using XMM data, characterized by relatively low spatial resolution, for detecting and analyzing such features, highlighting the challenges and potential biases introduced by instrumental constraints.

We prove the existence of solutions to the Lorentzian Monge problem on synthetic Lorentzian spacetimes that satisfy the forward timelike measure contraction property $TMCP^+(K,N)$. The cost for this problem is the time separation function $\ell(x,y)$ (the Lorentz distance), which represents the maximum amount a particle can age when traveling from $x$ to $y$. The solution is based on the needle decomposition technique, and amounts to a reduction of the full problem to its one-dimensional counterparts. As an application of needle decomposition, we show that the Lorentzian timelike measure contraction property $TMCP^+(K,N)$ is equivalent to the $TMCP^+_{rLip}(K,N)$ condition, where the curvature dimension conditions are defined on gradient flow curves of reverse 1-Lipschitz functions.