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Whether cold dense quantum chromodynamics (QCD) matter undergoes a strong first-order phase transition remains an open question. In nature, neutron stars provide the most direct probe of cold dense QCD matter. Theoretically, chiral effective field theory constrains the equation of state of dense matter near nuclear saturation density, while perturbative QCD calculations constrain it at densities well beyond stable neutron-star interiors. We perform Bayesian inference with nonparametric Gaussian-process equation of state for β-equilibrated neutron-star matter under the assumption with and without a strong first-order phase transition, using the tidal deformability from GW170817; the NICER mass--radius measurements of PSR J0740+6620, PSR J0030+0451, PSR J0437-4715, and PSR J0614-3329; chiral effective field theory; and perturbative QCD. Within this Bayesian inference framework, the model comparison mildly to moderately favors a strong first-order phase transition, with its onset most likely lying above the central density of the most massive neutron star. Such an onset reconciles the stiffness required to support massive neutron stars with the softening favored by perturbative QCD from asymptotically high density.

NICER observations of millisecond pulsars (MSPs) suggest that non-dipolar magnetic fields are required in order to explain their surface X-ray hotspots. C. Kalapotharakos et al. modeled the NICER light curve of MSP J0030+0451 (J0030) using a static-vacuum offset dipole-plus-quadrupole field and corresponding force-free (FF) solutions to jointly reproduce the X-ray and Fermi-LAT γ-ray emission. We substitute their static-vacuum field model with a more realistic swept-back configuration that accounts for rotational effects. This field more closely resembles the corresponding FF solutions, making it a more physically motivated choice for future multiwavelength modeling. We adopt a centered swept-back vacuum multipolar magnetic field (SVM2F; J. Pétri), expressed as a complete expansion in vector spherical harmonics, enabling flexible descriptions of arbitrary magnetic field geometries. We introduce a metric to quantify the complexity among different field prescriptions, illustrated for the static offset vacuum field. To efficiently explore parameter space, we train a neural network surrogate (G. Olmschenk et al.) on SVM2F light curves, including components up to the octupole, accelerating Markov chain Monte Carlo sampling by ~10<SUP>3</SUP> compared to direct physical model evaluations. Applying this framework to J0030, we constrain the field parameter space and find that a centered swept-back multipolar field including terms up to the octupole adequately reproduces the bolometric thermal X-ray light curve. Our study highlights the importance and inherent complexity of prescribing different multipolar magnetic field models for rotating stars, and can be extended to other MSPs to ultimately constrain the masses and radii of neutron stars, and hence their equation of state.

We investigate Bayesian chiral effective field theory (χEFT) uncertainties, which assign a statistical interpretation to equation of state (EOS) distributions near nuclear saturation density, n<SUB>0</SUB>, as well as constraints from perturbative quantum chromodynamics (pQCD) to Bayesian EOS inference from LIGO/Virgo, NICER, and pulsar mass observations. The tails of the χEFT uncertainties allow for broader pressure ranges in our priors, but large parts of these are excluded by the astrophysical observations so that the EOS and the resulting mass--radius posteriors are still very consistent with our earlier work. Within our broad prior ranges, we observe a clear stiffening of the EOS at n ≳ 3n<SUB>0</SUB>. Moreover, the impact of the pQCD constraints on the posterior EOS and mass--radius range is negligible due to the astrophysics constraints. Exploiting the strong correlation between pure neutron matter and matter in beta equilibrium, we infer the symmetry energy slope parameter L from astrophysics. For the 68% credible interval, we obtain L = 42.6--52 MeV and L = 44.2--56.7 MeV using piecewise-polytrope and speed-of-sound high-density extensions, respectively. The L posterior is mainly driven by the combination of GW170817 LIGO/Virgo and PSR J0740+6620, PSR J0437-4715, and PSR J0614-3329 NICER observations.

We investigate the influence of ideal Fermi gas dark matter on the observable properties of neutron stars (NSs). Our analysis considers dark matter (DM) particle masses (μ) ranging from 0.2 GeV to 1 GeV and various DM mass fractions (f). By examining the coexistence of DM and baryonic matter (BM), we explore the formation of either a dense DM core or an extended dark halo within NSs. Our findings indicate that the resulting DM distribution depends critically on both μ and f. We systematically explore the parameter space of the fermionic DM model using two representative BM equations of state (EoSs) by applying constraints from NS radius measurements by the Neutron Star Interior Composition Explorer (NICER), observations of 2 M <SUB>⊙</SUB> NSs, and tidal deformability limits from the LIGO/Virgo collaboration. This comprehensive analysis enables us to exclude specific ranges of μ and f, demonstrating that the amount of accumulated DM must be relatively small to satisfy current astrophysical constraints.

Context. In May 2024, NOAA active region (AR) complex 13664/8 appeared as one of the most productive regions of the current solar cycle. It produced 12 X-class flares and over 20 coronal mass ejections (CMEs), triggering the strongest geomagnetic storm since 2003. Aims. We investigated why the AR complex is so productive, particularly in CMEs. Methods. Primarily using observations from the Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory, we analyzed the photospheric magnetic evolution, eruption sources, and eruption waiting times and compared the magnetic parameters with five other ARs. Results. The region initially comprised 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 non-potentiality. A comparison with five other ARs suggests that both flare-rich and CME-rich ARs exhibit elevated overall non-potentiality, as indicated by their high total magnetic free energy density and total current helicity, while CME-rich ARs exhibit particularly large mean current helicity, possibly implying stronger localized non-potentiality. The increased complexity manifests through at least 12 emerging bipoles and six collisional polarity inversion lines (cPILs) formed between nonconjugated polarities. All six cPILs exhibit sustained collision and shearing, serving as eruption sources. Decay index distributions show systematically lower critical heights (&lt;45 Mm) for a torus instability above the CME sources. The CME waiting time distribution exhibits two peaks, suggesting that multiple cPILs enhance CME productivity by increasing both recurrent CMEs from the same location and disturbance-triggered CMEs from nearby locations. Conclusions. The results highlight that in addition to sufficient non-potentiality and rapid background field decay, a high degree of magnetic complexity accompanied by dynamical collisional shearing at multiple cPILs is crucial for the region's extreme CME productivity.

We present deep X-ray observations of the nearby X-ray-luminous galaxy cluster Abell 1795 obtained with the Einstein Probe Follow-up X-ray Telescope (EP-FXT), with a total exposure time of ~480 ks. Exploiting the large field of view and low particle background of EP-FXT, we directly measured the radial temperature profile of A1795 out to R<SUB>200</SUB> with full azimuthal coverage, which was shown to increase in line with the radius within 6' and then gradually decline toward larger radii. The surface-brightness residual map and 2D thermodynamic maps reveal a clockwise spiral structure extending from the cluster core towards the south-east, which traces low-temperature and low-entropy gas, which is also consistent with sloshing-induced cold fronts. In the north-west, the surface-brightness-enhanced region exhibits an arc-like high-temperature feature and both the temperature-derived and density-derived Mach numbers support the assumption that it is a weak shock. These substructures can be explained by a binary merger scenario: the perturbing subcluster induces sloshing during its first passage past the primary core and its subsequent return passage through the ICM might drive the shock towards the north-west. Our results indicate that relaxed galaxy clusters such as A1795 might still retain signatures of dynamical activity.

Supermassive black holes (SMBHs) and their host galaxies coevolve through channels such as hierarchical merging and active galactic nuclei (AGN) feedback, establishing tight scaling relations between SMBH masses and the properties of the host galaxies. These scaling relations, particularly those with host-galaxy bulge mass (M<SUB>b</SUB>) and stellar velocity dispersion (σ), are widely used to estimate SMBH masses. Galaxy mergers drive gas into the centers of galaxies, enhancing SMBH growth and stellar bulge growth but not necessarily in tandem, so it is necessary to determine if galaxies undergoing a merger still follow SMBH--host-galaxy scaling relations. In this study, we explore scaling relations in galaxy mergers by taking advantage of the well-established value-added catalogs in the Sloan Digital Sky Survey. These catalogs provide close galaxy pairs, AGN broad lines for SMBH mass measurements, and bulge--disk-decomposed stellar masses. We compare SMBH mass estimates from M<SUB>∙</SUB>--M<SUB>b</SUB> to SMBH mass estimates from AGN broad lines and find that SMBH mass growth outpaces the bulge for AGN residing in the secondary (less massive) bulge and for smaller physical separations between galaxies in a pair. Using our full sample of close galaxy pairs, we find that M<SUB>∙</SUB>--M<SUB>b</SUB> and M<SUB>∙</SUB>--σ predict significantly different fractions of major and minor black hole mergers, with M<SUB>∙</SUB>--M<SUB>b</SUB> predicting black hole mass ratios closer to 1:1 and 6%-20% more major mergers overall. These results have major implications, including for predictions of astrophysical gravitational waves and high-redshift overmassive SMBHs.

A careful characterisation of the noise processes in pulsar timing data is a prerequisite for pulsar timing array experiments. While single-pulsar noise analyses are crucial for both gravitational-wave searches and astrophysical studies, they are often computationally intensive and rely on running and comparing multiple fixed noise models. We present tPTABilby, a transdimensional Bayesian inference framework for single-pulsar noise analysis built on the Bilby library. The method flexibly models a wide range of noise processes like radiometer noise, pulse-phase jitter, intrinsic red noise, dispersion measure variations, and chromatic interstellar medium effects. By employing transdimensional sampling, tPTABilby simultaneously infers the number and type of active noise sources, providing a unified treatment of model selection and parameter estimation. We validate the methodology through simulations with known injected noise models, demonstrating accurate recovery of model probabilities and calibrated posterior distributions. We then apply this approach to a single pulsar, PSR J1713+0747, from a MeerKAT Pulsar Timing Array (MPTA) dataset, analysing the data with both tPTABilby and Enterprise, and subsequently compare the results with existing MPTA analyses through posterior predictive checks of the inferred noise spectra. Our results highlight the flexibility of transdimensional approaches to single-pulsar noise analysis, demonstrating consistency with standard fixed-model methods while providing a more statistically robust framework, and present tPTABilby as a simple and reproducible approach for Pulsar Timing Array inference.

Extremely low-metallicity H II regions have been observed with the goal of determining the primordial helium abundance (Y<SUB>p</SUB>). Y<SUB>p</SUB>, combined with standard Big Bang nucleosynthesis and the half-life of the neutron, provides a direct measurement of the number of neutrino families, but Y<SUB>p</SUB> must be measured very precisely to provide meaningful constraints on physics beyond the Standard Model. Here we describe a program to combine new Large Binocular Telescope (LBT) observations with a new analysis methodology to significantly improve the determination of Y<SUB>p</SUB>. The LBT, with its MODS and LUCI instruments, produces spectra, which, when combined with our new analysis methodology, are capable of delivering He abundances in individual H II regions with uncertainties of approximately 2% or less. Archival LBT/MODS spectra of standard stars over a 4 yr period enable the determination of a wavelength-dependent uncertainty in the MODS spectral response, resulting in improved relative emission line uncertainties. An optimized sample of low-metallicity galaxies has been selected with the goal of producing a determination of Y<SUB>p</SUB> with a precision of ~0.5%, sufficient to provide an independent constraint on the effective number of neutrino families of ~3%.

Searches for Lorentz invariance violation (LIV) in the neutrino sector have traditionally focused on non-standard neutrino oscillations induced by LIV in vacuum. In this work, we study anisotropic LIV in matter. First, we review vacuum LIV phenomenology, explaining the energy and direction dependence of sidereal modulations for anisotropic coefficients in the Standard Model Extension. We then demonstrate that for high-energy neutrinos, the interplay between anisotropic LIV operators and the Earth's matter potential produces distinct, observable signatures absent in the vacuum case. We identify a crossover regime where the energy-dependent LIV Hamiltonian becomes comparable to the matter potential, leading to strong interference effects. By analyzing the propagation of neutrinos through a realistic Earth model, we establish three key phenomenological consequences: (1) direction-dependent resonant enhancements of oscillation probabilities, (2) a macroscopic breakdown of neutrino-antineutrino symmetry for CPT-even operators, and (3) a significant increase of the ν<SUB>τ</SUB> flux due to LIV-driven injection of high-energy neutrinos into the τ regeneration cycle. These results highlight that accounting for the interplay between LIV and matter is essential for future LIV searches at large-scale neutrino telescopes.

Pulsar timing arrays' hint for a stochastic gravitational-wave background (SGWB) leverages the expectations of a future detection in the millihertz band, particularly with the LISA space mission. However, finding a SGWB with a single orbiting detector is challenging: It calls for cautious modelling of instrumental noise, which is also mainly stochastic. It was shown that agnostic noise reconstruction methods provide robustness in the detection process. We build on previous work to include more realistic instrumental simulations and additional degrees of freedom in the noise inference model and analyze the impact of LISA's sensitivity to SGWBs. Particularly, we model the two main types of noise sources with separate transfer functions and power spectral density spline fitting. We assess the detectability bounds and their dependence on the flexibility of the noise model and on the prior probability, allowing us to refine previously reported results.

In this paper we quantify the ability of the Laser Interferometer Space Antenna (LISA) to test the presence of non-tensorial polarizations as well as modifications to the tensor ones in gravitational waves emitted from massive black hole binaries. We employ the Parametrized Post-Einsteinian (PPE) formalism to model deviations from General Relativity (GR) for tensor, vector, and scalar polarizations. Our PPE parametrization is inspired by post-Newtonian waveforms from four modified gravity theories: Horndeski, Einstein-aether, Rosen's bimetric, and Lightman-Lee. We consistently implement these modifications during the inspiral, ensuring proper waveform alignment and tapering at merger. Subsequently, we perform Fisher forecasts to derive expected constraints on deviations from General Relativity and map these constraints to the parameter spaces of the four gravity theories. For tensor polarizations, LISA achieves constraints on amplitude modifications ranging between ~ 10<SUP>-4</SUP> - 10<SUP>-2</SUP> precision level, depending on the frequency evolution of the modifications, for systems with 10<SUP>5</SUP> - 10<SUP>7</SUP> M<SUB>⊙</SUB> at z = 1. We find that LISA can distinguish breathing and longitudinal scalar polarizations, a capability that current ground-based detectors do not possess, only for relatively light binaries with M ≲ 10<SUP>4</SUP> M<SUB>⊙</SUB>, beyond which these modes become degenerate in the detector response. Importantly, constraints on vector polarizations are approximately 2--3 times more precise than for scalar polarizations. For both vector and scalar modes, amplitude measurements reach precisions ranging between ~ 10<SUP>-8</SUP> - 10<SUP>-2</SUP>, depending on the frequency evolution of the modifications, for systems with 10<SUP>5</SUP> - 10<SUP>7</SUP> M<SUB>⊙</SUB> at z = 1. These results demonstrate LISA's potential to probe gravity in the emission process of gravitational waves.

We revisit the production of primordial black holes (PBHs) by a U(1) gauge field with a pseudo-scalar coupling to the inflaton. We improve upon the existing literature by working in the homogeneous backreaction regime with numerically computed gauge mode functions, adopting state-of-the-art PBH abundance calculations, and incorporating the uncertainty in the statistics of δρ. We find that PBHs can account for all of the dark matter in the asteroidal mass range, even when the inflaton gradient energy density is highly subdominant (10<SUP>-4</SUP>--10<SUP>-3</SUP> of the kinetic energy), supporting the validity of the backreaction scheme. This mechanism also unavoidably generates a stochastic gravitational wave background with an amplitude that will be measured at LISA and that will allow to indirectly discriminate between different statistics of δρ.

Context. The formation pathways of sulfur-bearing species in the interstellar medium (ISM) are crucial for our understanding of astrochemical processes in cold molecular clouds and gaining new insights into the sulfur budget in these regions. Aims. We aim to explore the recently detected thioethanal (CH<SUB>3</SUB>CHS) formation mechanisms from thioethanol (CH<SUB>3</SUB>CH<SUB>2</SUB>SH) as a precursor, in addition to secondary sulfur products. Methods. We employed electronic structure methods and density functional theory for both gas-phase and ice-grain surface environments. To mimic interstellar ice-mantles, we used both medium (W6) and large amorphous (W22) water clusters, as implemented in Binding Energy Evaluation Platform (BEEP). Results. We identified a formation mechanism that is effectively barrierless with respect to the reactant asymptote for CH<SUB>3</SUB>CHS, which remains kinetically feasible under low-temperature interstellar conditions, in the gas phase. Surface environments modulate activation barriers in a site-specific manner, elucidated through both Langmuir-Hinshelwood and Eley-Rideal initiated surface reaction pathways. Compared to oxygen analogs, sulfur chemistry enables alternate pathways due to weaker S--H bonding, with a competing route forming ethane-1,1-di-thiol (CH<SUB>3</SUB>CH(SH)SH) on the ice-grain surface, potentially reducing CH<SUB>3</SUB>CHS yields. The first accurate binding energy for thioethanol on water ice is also reported here, confirming its greater volatility in comparison to ethanol. Conclusions. The proposed mechanism offers a tentative hypothesis for the apparent mutual exclusive detections of CH<SUB>3</SUB>CH<SUB>2</SUB>SH and CH<SUB>3</SUB> CHS in TMC-1, Orion, and Sgr B2(N), which requires further validation through quantitative astrochemical modeling and also to distinguish this chemical differentiation from observational sensitivity limitations. These qualitative findings highlight the multifaceted chemical behavior of sulfur-bearing organics in the ISM and support CH<SUB>3</SUB>CH(SH)SH as a promising astrochemical target.

Context. In the central molecular zone (CMZ) environment, shocks play a key role in both triggering star formation and providing chemical enrichment. The Sgr B2 complex is a prime template, hosting several massive protoclusters (N, M, and S) and the northern G+0.693 cloud, which exhibits shock-induced prestellar signatures. Aims. We report on G+0.633-0.0604, a new shock-dominated and chemically rich cloud at the southern edge of Sgr B2, where it has been proposed that the next star formation episodes will occur. We characterise its physical properties and the shocks shaping it. Methods. We analysed data from new high-sensitivity broadband spectral surveys using the Yebes 40m, IRAM 30m, and APEX radio telescopes, covering a ~ 100 GHz aggregated bandwidth across the ~31-275GHz range. We present analyses of CH<SUB>3</SUB>CCH, CH<SUB>3</SUB>CN, HC<SUB>3</SUB>N, HNCO, and several isotopologues of CO to infer kinetic temperatures and H<SUB>2</SUB> densities. We complementarily used 3 mm IRAM 30m mosaics (~13'×13', ~32×32 pc<SUP>2</SUP>) of Sgr B2 in HC<SUB>3</SUB>N, HNCO, and C<SUB>2</SUB>H<SUB>5</SUB>OH to probe G+0.633's environment. Results. We identify three velocity components towards G+0.633: a narrow main one (C1, v<SUB>LSR</SUB>~48.5 km s<SUP>-1</SUP>; FWHM~10km s<SUP>-1</SUP>) and two broader, much fainter components at higher velocities, C2 (~61 km s<SUP>-1</SUP>; ~13km s<SUP>-1</SUP>) and C3 (~89km s<SUP>-1</SUP>; ~18km s<SUP>-1</SUP>), all of which show similar properties (T<SUB>kin</SUB>~55-90K, N<SUB>H<SUB>2</SUB></SUB>~(3-7)×10<SUP>22</SUP> cm<SUP>-2</SUP>, n<SUB>H<SUB>2</SUB></SUB>~(0.5-2.5)×10<SUP>4</SUP> cm<SUP>-3</SUP>) and extended distributions. C1 delineates G+0.633 physically, and corresponds to a peak in HNCO. This supports a shock-driven origin, likely rooted in the cloud--cloud collision shaping Sgr B2 and also traced by C2, which mainly extends north to G+0.693. C3 is kinematically unlinked and related to large-scale CMZ dynamics. Of the three, C1 may be consistent with a very early protocluster phase, but this is yet to be confirmed. Conclusions. G+0.633 emerges as a new shock-dominated CMZ cloud with a physical resemblance to G+0.693, providing another unique laboratory to investigate how shocks drive molecular complexity and regulate the onset of cluster formation in the CMZ.

The primordial abundance of <SUP>4</SUP>He plays a central role in Big Bang nucleosynthesis (BBN) and in the cosmic microwave background (CMB). The LBT Y<SUB>p</SUB> Project's new measurement of the primordial <SUP>4</SUP>He mass fraction, Y<SUB>p</SUB> = 0.2458 ± 0.0013, is the most precise determination to date. In this paper, we combine our new Y<SUB>p</SUB> value with the latest primordial deuterium measurement and assess the consequences for cosmology. For standard BBN, where the number of light neutrino species is fixed at N<SUB>ν</SUB> = 3, the single free parameter is the cosmic baryon density; the CMB measures this independently, with results consistent with each other. Combining Y<SUB>p</SUB>, D/H, BBN, and the CMB gives the cosmic baryon-to-photon ratio η = (6.120 ± 0.038) × 10<SUP>-10</SUP>, corresponding to a baryon density parameter Ω<SUB>B</SUB>h<SUP>2</SUP> = 0.02236 ± 0.00014. We then allow N<SUB>ν</SUB> to vary and thus measure relativistic species present during nucleosynthesis. We find η = (6.101 ± 0.044) × 10<SUP>-10</SUP> or Ω<SUB>B</SUB>h<SUP>2</SUP> = 0.02229 ± 0.00016, and N<SUB>ν</SUB> = 2.925 ± 0.082, and for N<SUB>ν </SUB>&gt;= 3, ∆N<SUB>ν</SUB> = N<SUB>ν</SUB> - 3 &lt;= 0.125 (95% confidence limit) during BBN and the CMB. Our results demonstrate consistency with the Standard Model of particle physics and the standard cosmology that links BBN at <inline-formula> <mml:math><mml:mo>~</mml:mo><mml:mn>1</mml:mn><mml:mspace></mml:mspace><mml:mi>s</mml:mi></mml:math> </inline-formula> and the CMB at ~400,000 yr.

We report the first proper motion and acceleration measurements of the infrared (IR) counterpart to Sagittarius A* (Sgr A*-IR), the supermassive black hole at the center of our Galaxy, in the Gaia Celestial Reference Frame 3 (Gaia-CRF3). This reference frame realizes the International Celestial Reference System, which is an absolute reference coordinate system defined by quasars. A combination of Gaia and Hubble Space Telescope data was used to transform Keck adaptive optics observations into Gaia-CRF3. We developed a method for selecting reference stars that minimizes astrometric transformation errors (statistical error = 0.10--0.63 mas) and drift of the coordinate system (systematic error ~ 0.01 mas yr<SUP>-1</SUP>). We find the proper motion of Sgr A*-IR in Gaia-CRF3 to be <inline-formula> <mml:math><mml:msub><mml:mrow><mml:mi>μ</mml:mi></mml:mrow><mml:mrow><mml:msup><mml:mrow><mml:mi>α</mml:mi></mml:mrow><mml:mrow><mml:mo>*</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mo>-</mml:mo><mml:mn>3.093</mml:mn><mml:mo>±</mml:mo><mml:mn>0.085</mml:mn></mml:math> </inline-formula> mas yr<SUP>-1</SUP> and μ<SUB>δ</SUB> = -5.62 ± 0.13 mas yr<SUP>-1</SUP> with the initial position at t<SUB>0</SUB> = 2016.0 of R.A. = 266<inline-formula> <mml:math><mml:mover><mml:mrow><mml:mo>.</mml:mo></mml:mrow><mml:mrow><mml:mtext>°</mml:mtext></mml:mrow></mml:mover></mml:math> </inline-formula>41680848 ± 0<inline-formula> <mml:math><mml:mover><mml:mrow><mml:mo>.</mml:mo></mml:mrow><mml:mrow><mml:mtext>°</mml:mtext></mml:mrow></mml:mover></mml:math> </inline-formula>00000029 and decl. = -29<inline-formula> <mml:math><mml:mover><mml:mrow><mml:mo>.</mml:mo></mml:mrow><mml:mrow><mml:mtext>°</mml:mtext></mml:mrow></mml:mover></mml:math> </inline-formula>00783947 ± 0<inline-formula> <mml:math><mml:mover><mml:mrow><mml:mo>.</mml:mo></mml:mrow><mml:mrow><mml:mtext>°</mml:mtext></mml:mrow></mml:mover></mml:math> </inline-formula>00000050, which translates to a precision of 1.05 mas in R.A. and 1.79 mas in decl. This is consistent with the astrometric measurements of the radio counterpart to Sgr A* by S. Xu et al. We also place a 2σ upper constraint of the acceleration of Sgr A*-IR on the sky at 0.061 mas yr<SUP>-2</SUP>. This acceleration limit on Sgr A*-IR excludes any intermediate-mass black hole companion with mass ≳ 4 × 10<SUP>4</SUP> M<SUB>⊙</SUB>within a distance of ~0.01 pc, consistent with previous studies. With the release of Gaia Data Release 4, we predict these limits will be improved by at least a factor of 2.

We study how quasinormal-mode frequencies may encode information about the effective matter source responsible for black-hole hair. Using the established eikonal correspondence between quasinormal modes and unstable null geodesics, we relate shifts in the ringdown spectrum to perturbations of the photon-orbit frequency and Lyapunov exponent. The black-hole hair is treated as an anisotropic fluid perturbatively added to vacuum black holes (Schwarzschild and Kerr black holes). In particular, we derive formulas that allow one to directly read off deviations from the Schwarzschild or Kerr QNM spectrum in terms of the corresponding equation-of-state parameters of the anisotropic fluid. In this setting, independent of energy conditions, our formulas offer a systematic method to compute quasinormal-mode frequencies for a broad class of hairy black holes.

We propose a baryogenesis mechanism in which an electroweak phase boundary is induced by a wall-like configuration of a scalar field, such as a domain wall or a shock wave, coupled to the Higgs field. If the Higgs mass parameter depends on the scalar field value, the wall locally separates the electroweak-symmetric and broken phases, thereby providing an induced electroweak wall. We focus on the case where the scalar field is an axion-like particle coupled to the SU(2) Chern--Simons density. The motion of the wall then generates a local effective chemical potential for B+L, realizing a spontaneous baryogenesis mechanism. In the presence of unsuppressed sphaleron transitions in front of the wall, this biases the plasma and leads to baryon asymmetry generation. We discuss the parametric conditions for the induced wall, cosmological realizations based on domain walls and shock waves, and the associated implications for baryon inhomogeneities and gravitational waves. The axion coupling is predicted to be sufficiently weak to evade current experimental and observational bounds.

We present the Ripples of Stellar Enrichment (RoSE) simulations, which follow an isolated Milky Way-mass disc galaxy with star-by-star feedback and nucleosynthesis from five physical enrichment channels - Wolf-Rayet stars, type II supernovae, type Ia supernovae, asymptotic giant branch stars, and neutron star mergers. We use these simulations to test how elements' diverse nucleosynthetic origins imprint spatial, temporal, and inter-element abundance correlations in gas and newly formed stars. We find that nucleosynthetic source composition is the primary organising principle of elemental structure: elements sharing a dominant production channel exhibit similar spatial and temporal statistics and their abundances are strongly correlated with one another, while mixed-source pairs are much more weakly correlated. We show that a simple linear regression model based only on how element pairs differ in their nucleosynthetic origin is able to predict, with high fidelity, how strongly their abundances correlate, in both interstellar medium gas and coeval stars. Comparison with Milky Way stellar abundance data shows encouraging qualitative agreement, with differences between simulations and observations comparable to the scatter between independent observational datasets. Together, these results show that the covariance of galactic abundances is largely predictable from the mixture of nucleosynthetic sources supplying each element: same-source elements remain tightly correlated in gas and young stars, whereas differing source mixtures produce systematically weaker correlations.

Future gravitational-wave detectors, such as the Einstein Telescope and Laser Interferometer Gravitational Wave Observatory (LIGO) Voyager, are planned to implement cryogenic technology. For the Kamioka gravitational wave detector, where cryogenics has already been adopted, issues related to the growth of an ice layer on mirror surfaces were reported. Further studies have confirmed the presence of nanometric layers in cryogenic experiments in which ice led to an increase in optical loss and to oscillations of the mirror reflectance. In this study, we investigate the mechanical loss of an ice layer grown on a silicon substrate. The results show that the total mechanical loss increases over time with the thickness of the ice layer, indicating that even a few nanometers of ice can impact the sensitivity of gravitational-wave detectors.

We present a quotient-space Bayesian formulation for DESI-Era anomaly interpretation. Given a pattern-labeled catalog with map <inline-formula><mml:math><mml:mrow><mml:mi>i</mml:mi><mml:mo>↦</mml:mo><mml:mi>A</mml:mi><mml:mo>(</mml:mo><mml:mi>i</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:math></inline-formula>, the induced posterior <inline-formula><mml:math><mml:mi>p</mml:mi><mml:mo>(</mml:mo><mml:mi>A</mml:mi><mml:mo>|</mml:mo><mml:mi>D</mml:mi><mml:mo>)</mml:mo></mml:math></inline-formula>, sector inclusion probabilities <inline-formula><mml:math><mml:msub><mml:mi>P</mml:mi><mml:mi>α</mml:mi></mml:msub></mml:math></inline-formula>, coactivation probabilities <inline-formula><mml:math><mml:msub><mml:mi>P</mml:mi><mml:mrow><mml:mi>α</mml:mi><mml:mi>β</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula>, and grouped Bayes factors <inline-formula><mml:math><mml:msub><mml:mi>B</mml:mi><mml:mi>α</mml:mi></mml:msub><mml:mo>(</mml:mo><mml:mi>D</mml:mi><mml:mo>)</mml:mo></mml:math></inline-formula> are exact summaries over predeclared physical activation events. Pairwise comparisons such as <inline-formula><mml:math><mml:mi>Λ</mml:mi><mml:mi>CDM</mml:mi></mml:math></inline-formula> versus <inline-formula><mml:math><mml:msub><mml:mi>w</mml:mi><mml:mn>0</mml:mn></mml:msub><mml:msub><mml:mi>w</mml:mi><mml:mi>a</mml:mi></mml:msub><mml:mi>CDM</mml:mi></mml:math></inline-formula> remain ordinary Bayes-factor tests between specified families; the quotient construction addresses the coarser question of which physical sector carries posterior support when different sectors are represented by unequal numbers of catalog elements. We derive a sector-resolved DESI-CMB-SN likelihood specification for late-time background, early-time ruler, supernova calibration, perturbation, and gravitational-wave propagation sectors. The construction includes an Alcock-Paczynski/isotropic-scale BAO decomposition, a pure-ruler projection, analytic marginalization of low-rank supernova calibration modes, Fisher-normalized sector priors, inactive-sector leakage tests, log-evidence uncertainty propagation, and prior/sector-partition diagnostics. The result is a quantitative procedure for reporting model-comparison support at the level of physically interpretable sectors.

The majority of the Milky Way's stellar halo consists of debris from our galaxy's last major merger, the Gaia-Sausage-Enceladus (GSE). In the past few years, stars from the GSE have been kinematically and chemically studied in the inner 30 kpc of our galaxy. However, simulations predict that accreted debris could lie at greater distances, forming substructures in the outer halo. Here we derive metallicities and distances using Gaia DR3 XP spectra for an all-sky sample of luminous red giant stars, and map the outer halo with kinematics and metallicities out to 100 kpc. We obtain follow-up spectra of stars in two strong overdensities---including the previously identified outer Virgo Overdensity---and find them to be relatively metal rich and on predominantly retrograde orbits, matching predictions from simulations of the GSE merger. We argue that these are apocentric shells of GSE debris, forming 60--90 kpc counterparts to the 15--20 kpc shells that are known to dominate the inner stellar halo. Extending our search across the sky with literature radial velocities, we find evidence for a coherent stream of retrograde stars encircling the Milky Way from 50 to 100 kpc, in the same plane as the Sagittarius Stream but moving in the opposite direction. These are the first discoveries of distant and structured imprints from the GSE merger, cementing the picture of an inclined and retrograde collision that built up our galaxy's stellar halo.

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.