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Spectral lines encode the velocity, the temperature, and the chemical structure of astrophysical gas; interpreting them requires radiative transfer that is accurate at high optical depth, consistent with the local excitation, and efficient enough to synthesize velocity-resolved images. We present Kratos-linerad, a GPU-accelerated Monte Carlo radiative transfer code for spectral lines. The level populations can be iterated to statistical equilibrium together with the escaping photon distribution, treating angle-dependent partial frequency redistribution through constant-memory sampling tables. The code adopts the two-step imaging scheme to line transfer, in which a Monte Carlo pass samples a velocity-resolved scattering emissivity, and a deterministic ray-tracing pass synthesizes channel maps decoupled from the scattering geometry. Validation reproduces the analytic scaling of escaped spectra and the imaging double-peak profiles. GPU parallelism enables both stages sufficiently fast for routine application to astrophysically realistic models.

We quantify pulsar timing array (PTA) sensitivity to anisotropy in the gravitational wave background using the cross-correlation based Fisher information matrix in the pixel and spherical harmonic bases. We use a set of simulations to empirically determine scaling relations of a PTA's sensitivity to anisotropy with the number of pulsars $N_\mathrm{psr}$ in the array, the error $δt$ on the times of arrival, the frequency $f_\mathrm{GW}$ of the gravitational waves, and the angular scale $ΔΩ$ of the anisotropy. The sensitivity scales approximately as $N_\mathrm{psr}^{0.8}$, $δt^{-0.08}$, and $ΔΩ^{1.6}-ΔΩ^{2.1}$ (depending on the ranges of $\ell$ and $m$ under consideration). In addition, we use realistic simulations to project the NANOGrav PTA sensitivity to a 30-year baseline and quantify the growth in sensitivity at several timeslices. Except at the lowest frequencies, we find negligible effect on sensitivity through increasing the observation duration only. Finally, we introduce a multi-resolution pixel basis motivated by the large dependence of the sensitivity on sky location, and demonstrate the operation of the basis through a set of injections and recoveries.

Ultralight bosons can trigger superradiant instabilities around rotating black holes, extracting angular momentum and leading in some cases to observable gravitational signatures. When the associated spin-down timescale is shorter than the black hole lifetimes and the spin-up timescales due to, e.g. accretion, this process imposes an upper limit on black hole spins. In addition, the formation and subsequent dissipation of boson clouds generates quasi-continuous gravitational wave emission. In this work, we explore the prospects for constraining and detecting ultralight bosons with observations of massive black hole binary mergers with the space-based LISA observatory. We consider two complementary approaches: measurements of black hole spins from merging binaries and follow-up gravitational wave searches targeting massive black hole binary merger remnants. We consider three population models for massive black holes, based on either heavy or light seeds, and forecast the exclusion and detection probabilities for both scalar and vector bosons. We find that black hole spin measurements can constrain scalar masses in the range $[5\times10^{-18},10^{-14}]$ eV and vector masses in the range $[6\times10^{-19},2\times10^{-14}]$ eV, with the exact range depending on the model. In contrast, restricting to vector bosons, follow-up gravitational wave searches are sensitive to a narrower vector boson mass range of $\sim[3\times10^{-17},3\times10^{-15}]$ eV, with the specific values again depending on the model. If a vector boson with a mass in the range $[10^{-16},2\times10^{-15}]$ eV existed, the probability of having an event that the follow-up searches would be sensitive to ranges from very small to near unity depending on the astrophysical model.

In this paper, we evaluate the precise distortion source and transfer functions caused by mixing of blackbodies of different temperatures using the recently developed frequency hierarchy (FH) treatment of CosmoTherm. With this we are able to evaluate the effects of primordial non-Gaussianity (PNG) on the $μT$, $μE$, $y T$ and $y E$ cross-power spectra including the coupled spectro-spatial evolution and important photon-transport effects retained by the FH treatment. For local-type PNG, we compare our results with those from previous works, illustrating new aspects that were previously not captured. We then demonstrate how the $μT$ and $μE$ signals change in the presence of enhanced curvature perturbations at small scales. For a nearly scale-invariant primordial spectrum, our results agree broadly with previous estimates on large angular scales but exhibit additional small-scale damping and modified $y$-distortion correlations arising from the scale dependence of the heating source and the distinct transport of distortion perturbations. Tight-coupling and monopole-source approximations accurately reproduce the $μ$-distortion spectra, while the $y$-distortion signals remain more sensitive to the detailed source evolution. For enhanced small-scale power, anisotropies generated by propagation of the distorted average spectrum can become comparable to those from anisotropic dissipation. Their different angular dependences and parameter scalings principally allow the small-scale power amplitude and primordial non-Gaussianity to be constrained separately. The results presented here thus pave the path for studying PNG in new regimes using existing and upcoming high precision CMB anisotropy data to measure primordial distortion correlations.

Context. Studies of the interstellar medium (ISM) have frequently revealed signatures of the dust produced in the envelopes of asymptotic giant branch (AGB) stars, demonstrating a connection between the dust composition of the ISM and that of AGB stellar envelopes. Investigating this relationship in the extreme, radiation-dominated environment surrounding Sgr A*, the center of our own galaxy, reveals how such conditions might influence dust composition and the recycling of material in galactic centers. Aims. IRS 3, the brightest L band source in the Galactic center and most prominent AGB star within the inner parsec of the Milky Way, is embedded in a dusty envelope with an estimated radius of ∼10 000 AU. We aim to conduct a comprehensive spectral analysis to more tightly constrain the dust composition and line-emitting species within the envelope of IRS 3 in the immediate vicinity of Sgr A*. Methods. In 2025, we observed the inner parsec of the Milky Way with the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) as part of the guaranteed time observations (GTO) program Mid-Infrared Characterisation of Nearby Iconic galaxy Centres (MICONIC). We used the MIRI Medium Resolution Spectrometer (MRS) to study the spectroscopic characteristics of the AGB star IRS 3, located about 0.17 parsecs in projection from Sgr A*. Results. After correcting for foreground dust extinction along the line of sight using a stellar-based mid-infrared extinction curve, we find a broad 9.7 μm silicate stretching feature accompanied by an O-Si-O bending mode absorption feature at 18.5 μm in the spectrum of IRS 3. We used the radiative transfer code Hyperion to model the observed spectrum of IRS 3 with a best-fit stellar luminosity of 60 000 L<SUB>⊙</SUB>. Based on our model, we find a multi-shell configuration that exhibits a significant temperature gradient between the inner and outer layers of the envelope. A combination of alumina and amorphous silicates accurately reproduces the observed spectrum. We infer a stellar mass of about 6 M<SUB>⊙</SUB> and a corresponding age of ≍72 Myr. For the first time, we find clear signs of water in the envelope of IRS 3. Conclusions. Based on our MIRI MRS observations and the modeled spectrum, we conclude that the dusty envelope of IRS 3 is consistent with a shell-like distribution with a temperature gradient of ≍1000 K. Analysis of the MIRI MRS spectrum reveals the presence of amorphous silicates, Al<SUB>2</SUB>O<SUB>3</SUB>, and H<SUB>2</SUB>O. A ratio of 3.5 ± 0.1 between the optical depth of the silicate Si-O stretching feature at 9.7 μm and the O-Si-O bending mode classifies IRS 3 as an O-rich star. Furthermore, assuming a wind velocity of v<SUB>w</SUB> = 15 km/s, we estimate a mass-loss rate of 6 × 10<SUP>−5</SUP> M<SUB>⊙</SUB> yr<SUP>−1</SUP> and identify H<SUB>2</SUB>O in the envelope of IRS 3. This finding demonstrates that the harsh radiation-dominated environment of Sgr A* does not inhibit dust formation or the survival of molecular species such as H<SUB>2</SUB>O.

We develop a variational calculus for curves on Fréchet manifolds and apply it to the Lagrangian formulation of the Einstein evolution equations on the manifold $\Mm$ of Riemannian metrics of a compact manifold. For mechanical Lagrangians associated with weak pseudo-Riemannian metrics, we establish the Euler--Lagrange equations, energy conservation, and an infinitesimal Noether theorem that does not require the symmetry vector field to generate a flow. Applied to the DeWitt Lagrangian, this framework identifies the momentum constraint with the vanishing of a Noether momentum map and gives a direct proof of its propagation. We also derive the pointwise transport identity \[ \partial_t\bigl(\Ham_λ\,\dv_g\bigr) = 2α\,δ_g(δ_g^-k)\,\dv_g\,, \] which implies propagation of the Hamiltonian constraint. Finally, we prove a Maupertuis-- Jacobi theorem for weak pseudo-Riemannian metrics on Fréchet manifolds and show that, away from the zero set of the total scalar-curvature potential, constrained Einstein evolutions are reparametrized unit-speed geodesics of the conformal DeWitt metric $-4αS_λG^-$.

We extend the modified double-copy construction to quasitopological gravity (QTG) coupled to matter. Spherically symmetric QTG solutions in $D$ dimensions are generated from an auxiliary gauge field in a flat $(D+1)$-dimensional spacetime. The gravitational field equations reduce to two relations determined by the QTG generating function and the matter stress--energy tensor. For a broad class of spherically symmetric matter sources, solutions of the auxiliary gauge-field equations can be used to construct exact solutions of the QTG field equations. The framework applies to Maxwell theory, nonlinear electrodynamics, and Yang--Mills theory, encompasses both static and Vaidya-type solutions, and reproduces the Einstein-gravity limit.

Cosmic voids provide a unique environment for studying the relationship between galaxies, subhaloes, and dark matter in the underdense Universe. Using the SDSS galaxy catalogue and the ELUCID constrained simulation, we establish an observationally anchored framework for measuring multi-tracer mass bias within matched cosmic voids. A sample of 102 matched void pairs is constructed to directly compare galaxy, subhalo, and dark matter mass distributions within an observationally constrained realisation of the local Universe. We find that both the galaxy-to-dark matter and subhalo-to-dark matter mass ratios decrease toward void centres, indicating that luminous and halo tracers become increasingly depleted relative to the underlying matter distribution in the deepest underdensities. In contrast, the galaxy-to-subhalo mass ratio exhibits substantially larger statistical uncertainties within the inner void regions ($r/R_{\rm v}\lesssim0.5$). By comparing measurements obtained using independent and common coordinate frameworks, we show that coordinate offsets contribute to the observed scatter but cannot fully account for the large uncertainties. The remaining uncertainty primarily arises from the severe scarcity of massive subhaloes ($\log_{10}(M_{\rm sub}/h^{-1}M_\odot)\ge11.8$) within void interiors, which greatly reduces the number of statistically valid measurements near void centres. Our results provide a direct measurement of multi-tracer mass bias in observationally constrained cosmic environments and highlight the fundamental statistical limitations of multi-tracer studies in extreme underdense regions.

Parity violation in the gravitational and electromagnetic sectors has been extensively investigated, yet the two are conventionally treated as independent phenomena. This separation, however, may be a four-dimensional prejudice. In higher-dimensional spacetime, gravity and electromagnetism may share a common geometric origin---and so, perhaps, does their parity violation. In this paper, we pursue this idea by constructing parity-violating Kaluza-Klein models in both Riemannian and teleparallel geometries. In Riemannian geometry, the simplest five-dimensional parity-violating term reduces to several complicated four-dimensional terms, including the familiar gravitational Chern-Simons term, which suffers from a ghost instability. In teleparallel geometry, however, the result is strikingly simple. The simplest five-dimensional parity-violating term reduces to only two ghost-free terms---the familiar Nieh-Yan term and the standard electromagnetic Chern-Simons term. Remarkably, the model predicts that the helicity-dependent dispersion shift for electromagnetic waves is exactly six times that for gravitational waves, $Δω^{2}_{ EM}=6\,Δω^{2}_{GW}$, a background-independent relation. This relation offers a falsifiable test of unification through joint cosmic microwave background and gravitational wave birefringence observations.

We investigate the geodesic dynamics, eikonal quasinormal modes (QNMs), and extended phase space thermodynamics of a Schwarzschild-de Sitter-like black hole coupled with a global monopole in Bumblebee gravity. Our analysis reveals that spontaneous Lorentz symmetry breaking and topological defects modify the effective radial dynamics, leading to lower effective potential barriers and a reduced magnitude of the effective force. For null geodesics, higher monopole parameters expand the photon sphere and critical impact parameter, implying an enlarged black hole shadow, while mitigating dynamical instability. For massive particles, the stable circular orbit window narrows significantly as the Outermost Stable Circular Orbit (OSCO) shrinks, alongside a marked enhancement in perihelion precession. In addition, we examine the correspondence between the eikonal QNMs and the properties of null geodesics. The excellent agreement between the eikonal approximation and the WKB method for scalar and electromagnetic perturbations supports the validity of the correspondence for the spacetime under consideration. In the extended thermodynamic phase space, we evaluate the black hole as a holographic heat engine. We demonstrate that classical efficiency is mathematically blind to Lorentz violation; however, introducing a quantum-corrected modified entropy tightly couples the macroscopic work output to the symmetry-breaking framework. Ultimately, the necessity to respect the Carnot bound imposes a strict macroscopic constraint on the Lorentz-violating parameter, safeguarding the Second Law of Thermodynamics.

Based on the fractional entropy from fractional quantum mechanics, fractional holographic dark energy (FHDE) has been proposed with the Hubble horizon as the IR cutoff (FHDEH). We extend this framework by adopting the future event horizon and the particle horizon as the IR cutoff, proposing the FHDEF and FHDEP models. Using the SN+OHD+DESI DR2 dataset to constrain these models, we find that all three models provide a marginally lower $χ^{2}_{min}$ compared to $Λ$CDM but without significant preference according to AIC and BIC. When CMB distance priors are included, the FHDEH and FHDEP models are strongly ruled out. We further analyze the cosmological evolution for these models, and find that only the FHDEF model predicts nearly identical evolutions of $Ω_{m}$ and $Ω_{de}$ to those of the $Λ$CDM model across cosmic history, but its deceleration parameter $q$ deviate from the $Λ$CDM model in the future, indicating richer late time dynamics beyond the standard $Λ$CDM cosmology.

We investigate Big-Bang Nucleosynthesis (BBN) in the context of Yukawa cosmology. We first derive the modified Friedmann equations by starting from the first law of thermodynamics on the apparent horizon. Using observational data on \(^4\mathrm{He}\), deuterium, and \(^7\mathrm{Li}\) abundances, we place stringent bounds on the Yukawa coupling \(α\). The \(^4\mathrm{He}\) and deuterium constraints are mutually consistent (\(-0.24 \lesssim α\lesssim 0.12\)), while \(^7\mathrm{Li}\) requires $α\in [-0.76,\,-0.72]$. This indicate that Yukawa cosmology cannot resolve the Lithium Problem. We then extend our analysis to WIMP freeze-out, and show that the modified Hubble parameter alters the relic abundance, yielding an independent constraint \(-0.017 \lesssim α\lesssim 0.018\) from \(Ω_{\mathrm{CDM}}h^2 = 0.120 \pm 0.001\). We also derive the modified time-temperature relation, and show that the positive \(α\) raises the early Universe temperature. Our analysis demonstrates that BBN and dark matter relic abundance serve as complementary probes of modified gravity. Our studies confirm that Yukawa cosmology is a testable framework for early-Universe physics.

We present the highest resolution global MHD simulations to date of gas flow around a low mass a perturber with mass ratio $q\in[10^{-4},10^{-3}]$, embedded in an accretion disk around a massive central object. We find that gas flow onto the secondary self-consistently forms a turbulent, magnetized mini-accretion disk. The mini-accretion disk sustains a large-scale magnetic field generated by the dynamo effect of the MRI and the accretion flow into the perturber. Simultaneously, a bipolar, collimated, magnetized outflow is launched, extending beyond the perturber's Hill sphere. The bipolar outflows are driven by the combined action of magnetic pressure, in the innermost regions of the mini-accretion disk, and the magnetocentrifugal acceleration of gas, which may attain speeds comparable to the escape velocity from the massive central object. Our results establish an important conceptual connection in accretion disk physics across a wide range of astrophysical systems -from mini-accretion disks to circumstellar and black hole accretion disks-by demonstrating that no fine-tuning is required for small-scale disks to naturally enter an outflow-launching regime. Beyond identifying the physical mechanism responsible for launching small-scale outflows, our framework lays the groundwork for developing more sophisticated physical models of mini-accretion disks around embedded low-mass perturbers.

We investigate the imprints of a dynamical Barbero--Immirzi (BI) field $γ(x)$ coupled to a quintessence scalar field $φ$ on gravitational-wave (GW) propagation. In the framework of Einstein--Cartan--Holst gravity, promoting $γ$ to a dynamical scalar introduces a stress--energy that back-reacts on the metric, modifying the GW friction term. A minimal coupling $\proptoβ\,φ^2γ^2$ between the BI field and quintessence leads to a two-parameter extension of the Belgacem--Maggiore parametrization, characterized by $\xBI$ (from the isolated BI field) and $\xcp$ (from the coupling). Using the LIGO--Virgo--KAGRA GWTC-3 dark-siren constraint $Ξ_0=1.2^{+0.7}_{-0.7}$, we obtain the first simultaneous constraints: $|\xBI|\lesssim0.7$ and $|\xcp|\lesssim0.13$ at 90\% credibility. We then forecast the sensitivity of next-generation detectors Einstein Telescope (ET) and Cosmic Explorer (CE), showing that a 10-year observation campaign can improve these bounds by roughly one to two orders of magnitude depending on the parameter---a factor of $\sim\!20$ for $\xBI$ and $\sim\!20$ for $\xcp$---reaching $σ(\xBI)\sim3\times10^{-2}$ and $σ(\xcp)\sim1.2\times10^{-2}$. Translated into microscopic parameters, this corresponds to $γ_{\rm dyn}\lesssim10^{-12}$ and $β\lesssim10^{-3}$, providing a powerful new observational window into the interplay between quantum-gravity phenomenology and dark energy.

Four planetary nebulae (PNe), Jonckheere 320, NGC 2610, A 6672, and PRTM 1, have been imaged in the far-ultraviolet (FUV) filter F148W ($λ_{\mathrm {eff}} = 1481\, \mathring{A} $) using the Ultraviolet Imaging Telescope (UVIT) onboard ASTROSAT. The FUV images reveal faint extended emission structures surrounding the bright central star. A novel sector-based structural analysis technique was employed to examine the detailed FUV morphologies of PNe. In this method, sector strengths were calculated for each nebula and used to classify their structures. Our results show that Jonckheere 320 exhibits a polypolar morphology, while NGC 2610 and PRTM 1 display spherical structures. In contrast, A 6672 shows irregular or elliptical features in the FUV.

Compact spatial topology restricts the eigenmodes of primordial tensor perturbations, and the resulting discreteness can render the primordial stochastic gravitational-wave background (SGWB) anisotropic. Here we treat the CMB tensor $B$-mode covariance as a transfer-filtered measurement of that ultra-low-frequency anisotropy. Writing the normalized angular tensor-power measure as $F(k,\hat k)=1+Q(k,\hat k)$ and its nonmonopole moments as $q_{LM}(k)$, we obtain an explicit kernel that maps $q_{LM}(k)$ onto the off-diagonal covariance $δC^{BB}_{\ell m,\ell' m'}$. The kernel factorizes into tensor transfer functions and a spin-weighted Gaunt coefficient and obeys the parity rule $L+\ell+\ell'$ even for $BB$ and odd for $TB/EB$. It is an exact source--response representation of the full compact covariance rather than an additional observable. For a cubic three-torus the geometry pins down a common cubic angular subspace and orientation across frequency bands, although the amplitudes of the allowed multipoles still depend on the radial shell and source spectrum. The same topology-restricted template can therefore be read out either through the CMB $B$-mode kernel or through the anisotropy response of PTA/LISA/Taiji/TianQin searches. Using CAMB transfer functions and an invariant anisotropic-template statistic, we contrast this tensor channel with the scalar $T/E$ covariance. Independent direct angular-shell sums and $q_{LM}$--Gaunt contractions agree at $L_q^{\max}=2\ell_{\max}$ to relative Frobenius residuals of $1.4\times10^{-14}$--$3.0\times10^{-14}$. The scalar sector holds most of the practical CMB topology information; a fixed-template scan places the combined full-sky $S/N=1$ transition between $L/χ_*=2.34$ and $2.36$, while the $B$-mode channel remains subthreshold but isolates the primordial SGWB contribution.

In the recently proposed scenario, the cosmological bounce occurs because the initially contracting Universe is not empty. In the region close to singularity, matter contents of the Universe heat up and effectively become radiation. Then, the trace anomaly automatically provides bounce if the overall beta function in the matter sector is positive. Independent of the remaining open questions on the quantum field theory side, it is interesting to consider this model from the cosmological perspective. In the present work, we develop the general formalism which is a necessary step for exploring the primordial cosmological perturbations. The main technical development is the formulation of the low-energy version for the nonlocal part of the effective action. The complete form of this action can be done local using two auxiliary scalars. In our new version, there are more scalars, but this enables one to avoid higher derivatives.

We establish a trapped surface formation theorem for the spherically symmetric Einstein Yang Mills equations in a double-null gauge. The theorem concerns characteristic initial data posed on a pair of transversely intersecting null hypersurfaces and allows nontrivial incoming data. The proof extends the singular characteristic method of An and Lim for the Einstein Maxwell Charged Scalar Field System to the non-abelian Yang Mills setting, where the curvature coupling and gauge field nonlinearities introduce new structural difficulties. This paper constitutes the first part of a program toward weak cosmic censorship for the Einstein Yang Mills system.

We study the adiabaticity of the cosmological perturbations in the context of inflationary Einstein-Gauss-Bonnet theories. We focus on viable inflationary Einstein-Gauss-Bonnet theories which are compatible with the current Cosmic Microwave Background radiation experiments and also are compatible with the GW170817 observations. We derive the effects of the adiabaticity requirement on the Einstein-Gauss-Bonnet physical parameters and we show that the sound speed of the scalar perturbations and the propagation speed of the tensor perturbations are constrained. We consider two classes of inflationary viable and GW170817-compatible theories, and in the first class the adiabaticity is not violated during inflation, while in the second class the adiabaticity is violated only at the end of inflation. We discuss the effects of the adiabaticity violation in the second class of models. From our analysis, it seems that only one class of viable EGB inflationary theories, which is also compatible with the GW170817 event, is free from adiabaticity pathologies.

When a black hole rings after a merger, it emits gravitational waves at characteristic frequencies known as quasinormal modes (QNMs). In the eikonal limit, these modes are governed by the unstable circular light orbits that form the photon ring. In this work, we demonstrate that the ringing of a black hole has a precise thermal interpretation. A probe string propagating in the near-ring geometry acquires an induced Rindler horizon on its worldsheet, with a temperature set by the Lyapunov exponent of the photon ring. Out of this structure, the black hole QNMs emerge as thermal excitations, so that the characteristic ringing of a black hole is the retarded response of a thermal system living on the photon ring. We explicitly derive the QNM spectrum from two complementary perspectives: microscopically, via unstable transverse worldsheet fluctuations, and macroscopically, through the pole structure of the causal response function of an open thermal quantum system.

Ultra-high-energy cosmic rays ($E_{\rm CR} \gtrsim 1$ EeV) are the highest-energy particles known, signaling extreme particle processes at work in the universe. However, many aspects of their nature remain largely unknown, even after more than a century of study. Very-high-energy ($E_ν\gtrsim 1$ PeV neutrinos associated with cosmic-ray interactions, both during the acceleration process and propagation, would provide new insight into these extreme particles, as we have seen at lower energies with the dawn of TeV neutrino astronomy. Nevertheless, only a handful of such neutrinos have been observed thus far. A space-based observatory dedicated to studying cosmic rays, neutrinos, and photons would provide an unprecedented platform for observations of these extreme-energy messengers.

Rotating near-horizon extreme solutions of quadratic gravity are analyzed combining power series expansions and numerical calculations. Restricting to geometries with symmetries of the near-horizon extreme Kerr black hole (i.e., with the $\mathrm{AdS_2}$-structure), spherical horizon topology, and equatorial reflection symmetry, we introduce conformal coordinates simplifying the field equations of Einstein--Weyl gravity, i.e., quadratic gravity with vanishing scalar curvature. Employing the Frobenius analysis, we classify all power series solutions expanded around the equator as well as the poles, and obtain the recurrence relations. With the help of numerical analysis, we study fine-tuning of the free parameter to satisfy the global constraints on regular near-horizon extreme geometries. Computations of the horizon area, horizon scalar curvature, and rotational scalar reveal strong horizon deformations in some Bachian branches. Moreover, the absence of regular Bachian near-horizon geometries above a finite horizon area suggests an upper bound on the size of the corresponding extremal rotating black holes.

Motivated by recent detections of several aromatic nitriles in Taurus Molecular Cloud-1, we report laboratory and theoretical investigations of the vibrational spectroscopy and photochemistry of singly and doubly cyano-substituted benzene in solid para-hydrogen matrices. We compare the photochemistry of cyanobenzene (benzonitrile) and three dicyanobenzene isomers initiated by excitations at 193 nm. In addition, we report the photochemistry of deuterated cyanobenzene (d$_5$-cyanobenzene), enabling us to determine the major products produced during the cyanobenzene photodissociation. The major products observed in the photolysis of all the nitriles are HCN and HNC, which are likely produced by hydrogen abstraction from para-H$_2$ by the CN radical. This indicates that the major photodissociation channel involves cleavage of the bond between the ring and the nitrile group, forming the phenyl (or cyanophenyl) radical + CN. We observe secondary photoproducts similar to those found during benzene photolysis. Our findings may aid the interpretation of recent JWST mid-infrared observations of aromatics in photodissociation regions.

Envelope-embedded protostellar disks represent the earliest stage of protoplanetary disk evolution, but their masses and sizes are difficult to measure because disk emission is entangled with the envelope. We analyze 26 protostellar disk systems in Taurus using ALMA Band 7 (345 GHz; ~0.3'') and VLA Ka-band (33 GHz; ~0.2'') continuum observations, together with molecular-line data to constrain disk gas masses. At 345 GHz, the median flux density, dust mass, and radius are 71 mJy, 5.5 M_Mearth, and 28 AU, with 68% ranges of 54-107 mJy, 3.9-9.4 M_Mearth, and 25-39 AU. At 33 GHz, the corresponding medians are 0.43 mJy, 39 M_Mearth, and 32 AU, with ranges of 0.41-0.80 mJy, 34-52 M_Mearth, and 29-33 AU. Taurus Class I disks are fainter and less massive than those in Orion, comparable to Perseus Class I disks but fainter than Perseus Class 0 disks, and brighter and more massive than those in Ophiuchus. Within Taurus, Class 0/I disks are brighter than Class II disks at both frequencies, although their inferred dust masses are comparable at 345 GHz and slightly higher at 33 GHz. Radiative-transfer modeling of CO isotopologue emission yields a median gas mass of 6.7 x 10^-4 M_Msun. The resulting CO-inferred gas-to-dust ratios span a broad range, with a mean of 147 +/- 75, a median of 26, and a 16th-84th percentile range of 8-147. This distribution overlaps the Taurus Class II population at the low end and ISM-like or higher values, including the AGE-PRO Ophiuchus Class 0/I population, at the high end.

Working to second order in cosmological perturbation theory, we reconsider the Large Scale White Noise (LSWN) effect proposed in [2511.13866] and [2511.15803]. We demonstrate that the kurvature density variable $Δρ$ does indeed develop LSWN at second order. However, contrary to the claims of [2511.15803], we show that this is not inherited as an infrared (IR) pole in the second-order comoving curvature perturbation $R_2$. This apparent enhancement was an artifact of using a linear Poisson equation to relate two genuinely second order quantities. Further, we show that $R_2$ is protected from developing any such IR enhancement: $\lim_{k \rightarrow 0} \left( k^2 R_2 \right) = 0$, which follows from a conservation law in the soft limit. The constraint proposed in [2511.15803] and its implications for the small-scale primordial power spectrum are therefore invalid.

Molecular winds may play a key role in governing angular momentum transport and accretion during the early evolution of protostars. We present the morphology and kinematic properties of the H$_2$ emission in five young, envelope-dominated, protostars across a broad bolometric luminosity range, from 0.2 to $10^4~L_{\odot}$, observed with the NIRSpec/IFU and MIRI/MRS onboard JWST as part of the Investigating Protostellar Accretion (IPA) program. A rich set of pure rotational lines of H$_2$, up to $v=0-0$ S(18), and a few ro-vibrational lines are detected in the winds, revealing bipolar structures. The H$_2$ lines show a stratified/onion-like structure morphologically and kinematically, where the lines with higher $E_{\rm up}$ show a higher degree of collimation and higher velocities. Additionally, the wind velocity scales with the $L_{\rm bol}$ of the host protostellar system. In 4 out of 5 protostars, H$_2$ emission fills the outflow cavity without showing pronounced limb brightening. We also report a tentative detection of H$_2$ wind rotation in IRAS 16253, which suggests a launch radius of $\sim4$ au and the magnetic lever arm parameter of $\sim5-10$. Taken together, these properties of the H$_2$ winds can be explained by the magnetohydrodynamic disk wind models. We detect a collimated, high-velocity H$_2$ jet toward HOPS 370, which is more evolved than the extremely young source HH 211, but is accreting at a high accretion rate. This suggests that the presence of collimated molecular jets in protostars is more closely connected to accretion rate than system age.

The boundary quantity that captures the growth of black-hole interiors quantified by holographic complexity remains unknown beyond 2d dilaton gravity. We provide a critical analysis of a partition-function construction of Krylov spread complexity for thermofield-double states that provides a dimension-independent boundary reconstruction from semiclassical holographic partition functions, while developing the present dynamical and bulk construction for the BTZ saddle. In the double-scaled Sachdev-Ye-Kitaev model, where exact and semiclassical results can be compared, we show that the classical limit is reliable only when taken after the complexity has been reconstructed; taking this limit at the level of individual Lanczos coefficients discards essential information. Applying the construction to a large-central-charge two-dimensional conformal field theory above the Hawking-Page temperature dual to a Bañados-Teitelboim-Zanelli black hole, we find an intermediate departure from early-time quadratic growth followed by behavior compatible with a return toward asymptotically quadratic growth, rather than the linear late-time behavior of the volume and the standard finite-functional complexity = anything class. We then match this boundary behavior to a generalized complexity = anything bulk object built from an infinite series of extrinsic-curvature invariants. The construction provides a systematic route from black-hole thermodynamics to Krylov dynamics and can naturally be extended to higher-dimensional holographic black holes.

Shot-noise anisotropies in the nHz gravitational wave background (GWB) are a promising target for pulsar timing arrays (PTAs). If the nHz GWB is sourced by merging supermassive black hole binaries (SMBHBs), as current evidence suggests, the shot-noise signal is expected to be large, potentially of order unity at observing frequencies of $f \sim 1 \, \mathrm{yr}^{-1}$. In this regime, the signal is dominated by rare bright binaries, and Poisson fluctuations in the discrete SMBHB population produce significant spatial anisotropies. Here, we use Monte Carlo simulations to model the realization-to-realization scatter in the shot-noise, sampling from empirically calibrated models of the SMBHB source populations. We find that the probability distribution of shot-noise amplitudes is broad, spanning a factor of $\sim 50$ (95\% interval) at fixed frequency, with a long tail towards high amplitudes. The most probable and median amplitudes lie significantly below the ensemble means by factors of $\sim 2-3$, implying that the shot-noise in typical realizations is smaller than the mean. The ensemble-averaged shot-noise also differs from simple estimates based on moments of the strain, $\langle h^4 \rangle/\langle h^2 \rangle^2$, because the average of a ratio is not equal to the ratio of the averages (i.e., $\langle X/Y \rangle \ne \langle X \rangle/\langle Y \rangle$). This difference is a factor of $\sim 3$ at $f = 0.1 \, \rm{yr}^{-1}$, growing to larger than two orders of magnitude by $f \sim 1 \, \rm{yr}^{-1}$, where the GWB is dominated by low abundance, high-strain sources. Shot-noise nevertheless provides a powerful diagnostic for understanding the GWB and SMBHB populations; interpreting PTA measurements, however, requires modeling its full probability distribution.

Transient star-like objects of unknown origin have been identified in the first Palomar Observatory Sky Survey (POSS-1) as part of the Vanishing and Appearing Sources during a Century of Observations (VASCO) project. The source of the transients recorded by POSS-1 remains unknown, which is the warrant to coin the observed phenomena as Mysterious Transients (MT). We advocate an idea that the dark matter (DM) in form of the axion quark nuggets (AQN) made of standard model quarks (or antiquarks) and gluons, similar to the old idea of the Witten's strangelets, could {\it simultaneously} explain {\it all } the observed MT signals (including very short time scale for flash itself, association with nuclear test timing, observed alignments of several MT events, correlation with UAP reports, etc) collected or recorded for many years. Essentially we argue that the MT is a cousin of Ball Lightning (BL) events, also observed for centuries, without commonly accepted physics explanation. The basic parameters of this model (such as the typical baryon charge of the nuggets) had been fixed long ago by explaining the observed excess of radiation at variety of scales: from galactic to the solar, to local Earth's environments. In this work we use the same framework with the same set of parameters to study the observed MT phenomena. We also suggest several tests which substantiate or refute our proposal. We also present some suggestions on type of instruments required to study this specific (and well defined) type of the UAP events representing the cousins of BL and MT events in the AQN framework.

Blazars are a highly variable subclass of active galactic nuclei, whose relativistic jet is pointed towards our line of sight at a small angle. Their variability is often characterised by multi-band flares. BL Lacertae (BL Lac), the namesake of a blazar subclass recently exhibited the highest recorded linearly polarised optical flare. We investigate the origin of this flare via very-long-baseline interferometry observations. Our analysis shows that the sweeping, helical motion of the BL Lac jet, which is known to exhibit kink-like instabilities, can explain the observed flux density spike and polarisation angle rotation, as also confirmed by our state-of-the-art relativistic magneto-hydrodynamic simulations. As a by-product of these simulations we find that baryon loading of the jet is required to optimally replicate the observed jet morphology.

AF Lep b is one of the closest analogs to Jupiter in terms of mass ($3-4~M_{\rm{Jup}}$) and semi-major axis ($9$ AU) amenable to spectroscopic characterization. We present JWST/NIRSpec high-contrast spectroscopy of the planet from $2.85-5.3~μ$m at $R\sim3000$, which provide detections of CO$_2$, H$_2$S, CH$_4$, $^{12}$CO (and $^{13}$CO), and H$_2$O, as well as complementary JWST/NIRCam imaging that captures the planet's continuum flux from $4.0-4.7~μ$m. Combining the JWST observations with spectra from VLTI/GRAVITY and VLT/SPHERE ($1.0-2.5~μ$m), we carry out atmospheric retrievals that include the effects of clouds and disequilibrium chemistry while allowing the C, O, and S abundances to vary independently. AF Lep b exhibits metal enrichment across C, O, and S with $\rm C/H=2.9\pm0.5$, $\rm O/H=3.7\pm0.6$, and $\rm S/H=4.7\pm0.7~\times$ solar (and stellar). The planet's slightly sub-solar C/O and C/S are consistent with formation near its observed location, and disfavor formation beyond the CO snowline. The sulfur enrichment in AF Lep b implies significant accretion of disk solids during formation, and we estimate the planet contains $56\pm7~M_{\oplus}$ of solids. The C, O, and S enrichment levels of AF Lep b are similar to those of Jupiter, and other super-Jupiters like HR 8799 bcde. We also show that the degree of atmospheric metal enrichment of these imaged planets is similar to the bulk metal enrichment of transiting gas giants with masses greater than $\sim1~M_{\rm{Jup}}$, suggesting that the process and efficiency of metal accretion for gas giants may not be strongly dependent on orbital distance or planet mass.

Well-founded models of nonlinear electrodynamics (NED) are typically characterized by an additional parameter associated with their deviation from linear electrodynamics. In addition to that, from a phenomenological point of view, one of the most intriguing results of NED theory is that photons follow null geodesics according to an effective geometry. In particular, for a two-parameter electromagnetic Lagrangian density, we might observe the vacuum birefringence phenomenon, i.e., photons can follow null geodesics according to two effective geometries. Over the past few decades, efforts have been made to better understand the role of effective light cones in NED theory, as well as to constrain the additional free parameters provided by the theory. We investigate the ModMax black hole (BH) geometry, which is a well-motivated NED-sourced BH based on a two-parameter Lagrangian density, via light and orbital mechanics, considering the Shapiro time, the Sagnac effect, the gravitational and kinematic shifts, and the orbital precession. We find that the corrections introduced by nonlinear electromagnetic fields can be significant. In particular, we show that the Shapiro time delay and the gravitational redshift are identical for both effective metrics, making these observables insensitive to the birefringent structure of ModMax electrodynamics. By contrast, the Sagnac effect and the kinematic shifts remain capable of distinguishing the two effective geometries. Moreover, the orbital mechanics investigation, considering the orbital periapsis precession of the S2 star around Sagittarius A$^{\star}$, provides an observational constraint on the coupling between the NED parameter and the charge-to-mass ratio of the ModMax BH. Generally speaking, we provide a step-by-step procedure for theoretically exploring signatures of NED fields and constraining the free parameters of NED-sourced BH models.

We explore the possibility of a Machian interpretation for the phenomena associated with asymptotically flat rotation curves in disk galaxies, providing an alternative to both the Lambda-Cold Dark Matter ($Λ$CDM) paradigm and MOdified Newtonian Dynamics (MOND). We argue that the MOND acceleration scale $a_0$ is likely not a new fundamental constant, but rather a manifestation of the cosmological scales of the observable Universe ($a_0 \sim c^2/R_u \sim c^4/GM_u \sim c/t_u$). We rewrite the Baryonic Tully-Fisher Relation (BTFR) in a cosmological format, $\frac{M_{\rm bar}}{M_{u}} = \left( \frac{V}{c} \right)^4$, suggesting that the transition to the non-Newtonian regime occurs when local accelerations become small enough to feel the global cosmic boundary, and showing that any Machian interpretation must fulfill a relation of this form. Furthermore, this framework naturally predicts a cosmological evolution of the BTFR normalization as the mass in the observable Universe evolves. We test these predictions against recent high-redshift observations ($z \sim 2$ and $z \sim 5$), finding that the data favor a flat, baryon-only, $Λ$-dominated quasi-de Sitter universe ($Ω_m \approx 0.05$, $Ω_Λ\approx 0.95$) over standard MOND or $Λ$CDM parameters. These results suggest that flat galactic rotation curves may be interpreted as compelling evidence in favor of Mach's Principle, in at least some of its versions.

Empirical gyrochronology relies on co-eval stellar associations to map stellar rotation as a function of mass and age. The accuracy of its age predictions is therefore limited by the number and quality of benchmark rotation sequences. The well-characterized clusters NGC-6811 (t ~ 1 Gyr) and NGC-6819 (t ~ 2.5 Gyr) bracket an intermediate-age interval in which stellar spin-down remains poorly constrained due to lack of available rotation data. At t ~ 1.3 Gyr, NGC-752 provides a critical benchmark within this gap, but previous measurements could not define the G- and K-dwarf rotation sequence needed for calibration. Here, we combine Gaia-based NGC-752 membership lists with literature rotation periods to map NGC-752's slow-rotator sequence for the first time. We identify a well-defined sequence intermediate between those of NGC-6811 and NGC-6819. Stars near Teff ~ 4500 K rotate more slowly than their counterparts in NGC-6811, indicating that stars experiencing stalled spin-down at ~1 Gyr have resumed appreciable spin-down by the age of NGC-752. Adopting an age of 1.3 Gyr for NGC-752, we further show that existing empirical gyrochronology models overestimate the ages of many G and early-K dwarfs by 20--50% because they lack intermediate-age calibration data, although uncertainty in the absolute age of NGC-752 may account for part of this offset. NGC-752 therefore provides a necessary anchor for improving rotational age estimates. This calibration is especially timely because Gaia DR4, Roman, and PLATO are expected to yield rotation periods for tens of millions of stars, making the age coverage of benchmark sequences a principal limitation on large-scale gyrochronology.

Some of the next steps for high-precision cosmology lie within the high-redshift, high-density universe. Spectroscopic survey experiments such as the Dark Energy Spectroscopic Instrument (DESI)'s second phase DESI Run 2 will shift towards probing Lyman Break Galaxy (LBG) populations from z$\sim$2 to z$\sim$4.5. For this faint sample, spectroscopic redshift measurement and sample decontamination remains a challenge, even after target selection. We propose an approach based on supervised weighted contrastive learning, in order to both learn a redshift representation for spectra and decontaminate the sample from quasars and low redshift emission line galaxies. This strategy generalizes the contrastive learning loss approach with continuous relationship weights, such that the network simultaneously learns redshift and classification tasks. The model shows stronger outlier classification and comparable redshift identification performances when compared to the previous network used for DESI (a modified version of QuasarNET) on the same dataset. In particular, contrastive learning is well suited to the small, visually-inspected sample used for training and testing, especially given the multi-task nature of this work.

We explore the $U(1)_{(B-L)_3}$ gauge symmetry under which only third generation fermions are charged. The cancelation of the $[U(1)_{(B-L)_3}]^3$ anomaly requires a chiral fermion, $χ_L$, singlet under the gauge group but charged under $U(1)_{(B-L)_3}$. This chiral fermion can play the role of thermal dark matter with a relic abundance set via the freeze-out scenario through the annihilation to pairs of the third generation fermions. In the quark mass basis, the new gauge boson will have off-diagonal couplings to the $b$ and $s$ quarks which can lead to a new contribution to $B^+\to K^+ν_τ\barν_τ$. We discuss the relevant bounds from the LHC searches for a new gauge boson, dark matter searches, electroweak precision data, $Υ$ decay, the CKM matrix and the $B_s^0-\bar{B}_s^0$ mixing. We entertain the possibility of explaining the $B^+\to K^+ν\barν$ excess recently reported by Belle II within this model.

Black-hole event horizons obey a set of evolution equations governing their intrinsic and extrinsic geometry. We study these equations in a \textit{two-timescale} perturbative expansion about a Kerr background and derive strong constraints on the coarse-grained horizon dynamics. At leading order, the coarse-grained linear shear vanishes, while the horizon exhibits an \textit{adiabatic rigidity}: the leading corrections to its angular velocity and inaffinity remain uniform on each horizon cut, while evolving on the slow timescale. We then provide a systematic procedure for transforming a perturbative bulk solution, given for example in Lorenz gauge, to an ingoing Newman--Unti gauge adapted to the horizon, allowing the perturbed horizon geometry to be extracted directly from the bulk metric. Finally, we formulate black-hole conservation laws associated with horizon symmetries, including energy, dynamical entropy, and angular momentum. We expand the charges through second order and their fluxes through third order in perturbation theory, providing a framework for future applications to horizon absorption and backreaction in extreme mass-ratio inspirals.

Paleo-detectors record and retain crystal damage in ancient minerals from nuclear recoils induced by dark matter scattering over geological timescales. Previous studies have shown that paleo-detectors can provide sensitivity to a variety of dark matter (DM) scenarios which is complementary to conventional direct-detection experiments. In this paper, we complete the first detailed study of how well paleo-detectors can reconstruct DM parameters or distinguish between different types of DM interactions with nuclei in the presence of a DM signal, considering both elastic and inelastic DM-nucleus scattering. For representative nuclear recoil track read-out scenarios, we demonstrate that weakly interacting massive particle (WIMP) DM masses can be reconstructed for a variety of Non-Relativistic Effective Field Theory (NREFT) interactions between WIMPs and nuclei. In particular, paleo-detectors are projected to be capable of reconstructing WIMP masses $\lesssim$ 10 GeV, a regime that is challenging for conventional direct-detection experiments; further, we find that paleo-detectors could reconstruct WIMP masses up to 1 TeV for hypothetical signals within their accessible parameter space, extending the mass range over which reconstruction is possible by up to a factor of $\sim 2$ compared with analogous studies of conventional direct-detection experiments. In addition, we demonstrate that paleo-detectors could discriminate between canonical spin-independent or spin-dependent NREFT interactions and non-canonical interactions which can depend on the relative velocity or momentum transferred between the WIMP and nucleus. Specifically, at WIMP masses $\gtrsim$ 10 GeV, we project that canonical NREFT interactions can be excluded by paleo-detectors in the cases of nearly all non-canonical interactions without measurement of nuclear recoil direction, which conventional experiments typically require.

Hadronically decaying particles with lifetimes $τ\gtrsim0.02\,{\rm s}$ are excluded by Big Bang Nucleosynthesis almost independently of their abundance: the mesons from their decays convert protons into neutrons faster than the reverse, and helium is overproduced. For heavy neutral leptons (HNLs), this blankets the couplings the upcoming accelerator searches can reach. We propose a scenario with large lepton flavor asymmetries in which HNLs evade it. A Dirac HNL decays into $π^+$ and its antiparticle into $π^-$, so an asymmetry between the two populations injects an excess of $π^+$, which converts the neutrons back to their standard abundance, while a cancellation between the asymmetries and the HNL decays keeps the shift in $N_{\rm eff}$ small. This opens the parameter space with $m_l+m_π\lesssim m_N\lesssim1\,{\rm GeV}$ and $τ_N\lesssim1\,{\rm s}$, including a substantial region within the reach of SHiP. A discovery there, combined with the BBN and CMB observables, would fix the primordial flavor asymmetries up to one remaining direction. The relic neutrino background and a possibly first-order cosmic QCD transition, a source of gravitational waves, may probe that direction, and with it the lepton asymmetry of the Universe.

Primordial black holes (PBHs) form through several distinct mechanisms, each imprinting a characteristic mass function that a single-mass treatment risks erasing. Building on the FRISBHEE code, we introduce FRISHBEE, implementing four mass functions--log-normal, power-law, critical collapse, metric preheating--in a multimodal framework, with spin modeled via Gaussian and Fishbach profiles. Crucially, each channel's weight is derived from the primordial collapse probability rather than fitted, tying the mass function to the power-spectrum amplitude--a link between inflationary model-building and CMB observables. Solving the Friedmann-Boltzmann equations for $M_{\rm PBH}^{\rm in}=10^{7}$~g in the pre-BBN window, we compute $ΔN_{\rm eff}$ for five distributions, three spin configurations, and three weightings. Extended mass functions enhance $ΔN_{\rm eff}$ over the monochromatic benchmark by factors of $\sim\!1.03$ (critical collapse) to $\sim\!1.84$ (log-normal), preserving the hierarchy $LN > MM > PL > MP > CC$ across the mass window $\{10^{5},10^{7},10^{8}\}$~g. Near-extremal spin ($a_{\star}=0.99$) and spin-2 dark radiation invert this trend: superradiant spin loss averages away faster in broad distributions than in a monochromatic population, letting the monochromatic approximation overestimate $ΔN_{\rm eff}$. Against CMB-S4 and Simons Observatory sensitivities ($σ\simeq 0.06$ and $0.05$), the monochromatic benchmark is undetectable for scalar dark radiation (sDR $=0$), while log-normal, power-law, and multimodal distributions reach $\sim\!1.6$--$1.7σ$; for spin-2 dark radiation the signal drops over an order of magnitude, with none detectable. The formation channel thus governs the magnitude and observational accessibility of the Hawking signal, establishing $ΔN_{\rm eff}$ as a discriminant between single- and multi-channel PBH formation scenarios.

A characteristic-polynomial formulation is already known for static perfect fluids in Lovelock gravity [Phys. Rev. D 113, 084008 (2026)]. We extend it to the complete anisotropic matter sector. For arbitrary dimension and independently coupled curvature orders, we derive closed, summation-free expressions for the density, radial pressure, tangential pressure and anisotropy in terms of a single polynomial \(W\), its derivatives and two derived polynomials \(V\) and \(U\). The dimension-dependent combinatorial coefficients are obtained directly from the generalized-delta antisymmetrisation and independently confirmed through an inductive argument. Imposing pressure isotropy recovers the known total-derivative equation, which we resolve into an explicit operator affine in Lovelock order and linear in dimension. This structure proves that, apart from the branch of vanishing angular sectional curvature, the interior Schwarzschild geometry is the unique isotropic interior common to arbitrary Lovelock couplings. It also identifies the fixed-sign obstruction to bounded pure Lovelock spheres in \(d=2N+1\) with the polynomial identity \(V\equiv0\), and shows how a lower-order term or cosmological term removes this obstruction. Finally, we integrate the resulting arbitrary-order stellar equations with all admissible orders active in \(d=10\) and \(d=11\). For the positive single-parameter hierarchy of Lovelock couplings considered, the general-relativistic sequence topology persists while higher orders increase the maximum mass cumulatively.

The Carruthers Geocoronal Observatory (Carruthers), formerly GLIDE, is a NASA Heliophysics Science Mission of Opportunity implemented through the Solar Terrestrial Probes (STP) Program and launched as a rideshare in September 2025. Carruthers is the first spaceflight mission edicated to continuous global imaging of Earth's hydrogen exosphere through observations of geocoronal Lyman-$α$ emission at 121.6 nm. The observatory operates at distances of 1.3-1.7 million km in a halo orbit about the Sun-Earth L1 point, enabling retrieval of the three-dimensional distribution of atomic hydrogen, the dominant constituent of the exosphere, on hourly timescales and unprecedented spatial resolution. These new data provide the key to understanding processes governing atmospheric escape, geospace coupling, and solar-wind interaction. Carruthers carries the GeoCoronal Imager (GCI), a dual-channel ultraviolet imaging instrument comprising the Narrow-Field Imager (NFI) for high-resolution observations of the inner exosphere and the Wide-Field Imager (WFI) for synoptic imaging of the extended hydrogen halo. Along with a student-provided experiment, the instrument suite is the sole payload aboard a three-axis-stabilized spacecraft designed to support nadir viewing throughout the $\sim178$ day halo orbit about L1. Observations also measure the interplanetary Lyman-$α$ background, enabling separation of heliospheric and geocoronal emissions. The student-led experiment monitors solar Lyman-$α$ and extreme ultraviolet emission during portions of the orbit. Science data are returned through the Deep Space Network at data rates up to 1 Mbit s$^{-1}$. The two-year baseline mission begins in March 2026, with propellant reserves capable of supporting more than ten years of orbit maintenance and maneuvers.

Neutron stars have baryon chemical potentials that can exceed the neutron mass, providing favorable conditions to convert neutrons to new particles carrying baryon number, even if those processes are kinematically forbidden in vacuum. We study the effect of GeV-scale scalars with baryon number on neutron stars' equation of state and show that non-perturbatively large repulsive self-couplings are required to support the observed two-solar-mass neutron stars. We also study potentials with attractive self-interactions, which can trigger scalar production even for masses above the chemical potential and resemble Coleman's Q-matter.

The binary T Tauri system, KH 15D, is poised to provide unprecedented detail of gas and ices located between $\sim$3-5 AU of its circumbinary disk over the next few years. We analyze for the first time a complete set of ground-based time series photometry of the KH 15D system for which the 2022 October - 2025 April data have never been presented. By combining the latest $I$-band data with historical measurements, we show that the era of large amplitude photometric variability has ended. We define a revised photometric period of $P$ = 48.365 $\pm$ 0.005 days, which accurately phases data over a time span of seventy-five years. We adopt magnitudes and colors for the stars that define the epochs when either star A (1995-2008) or star B (2010-2012) is the primary source of the out-of-eclipse brightness of the system. We determine for the first time the effective optical depth for the system between 2002 and 2025 assuming gray extinction. The current out-of-eclipse system color is consistent with a combination of the light from both stars, supporting the previously suggested model in which the trailing edge of the circumbinary disk is more transparent than the leading edge. We continue to see evidence for ``clumps'' and variable transparency along ingress and egress when the stars are probing the occulting material and suggest that observations made during these phases should permit studies of the physical and chemical nature of the planet-forming zone with the circumbinary disk.

Measuring the expansion rate of the Universe is a central challenge in cosmology. Independent and robust methods are essential to validate existing measurements and assess potential systematic effects. We employ the cosmic chronometer (CC) approach, which uses the differential age evolution of quiescent galaxies to measure the Hubble parameter H(z) without assuming an underlying cosmological model. In contrast to previous CC studies, we restrict our analysis to relics -- ultra compact massive galaxies (UCMGs) hosting the oldest stellar populations -- thereby minimising uncertainties related to star formation history and merger history. We select a sample of 189 relic galaxies in the redshift range 0.07< z <0.22 from the E-INSPIRE UCMGs catalogue. Using the D_n4000 spectral index of relic galaxies and its redshift evolution, combined with MILES stellar population synthesis models, we derive the differential age relation required to infer H(z). We account not only for metallicity effects but also for the impact of alpha-element enhancement, which has not been explicitly propagated into the systematic uncertainty budget of the D_n4000 cosmic chronometer method. We obtain an independent measurement of H(z=0.15) = 85\pm53 km/s/Mpc. The total uncertainty is dominated by statistical limitations. The systematic component is 13% (8.7% when alpha-enrichment is not propagated), among the tightest estimates in current CC studies. We find that alpha-enrichment plays a major role in the systematic error budget, particularly in the high metallicity regime, and must be properly accounted for in future analyses. We demonstrate the proof of concept that relic galaxies provide a promising pathway to reduce systematic uncertainties in the CC method. The statistical uncertainties, which dominate the error budget, can be significantly reduced by the increase of data volume expected during the next years.

We investigate the cosmological implications of Horava-Lifshitz (HL) gravity using a redshift-dependent deceleration parameter of the form $q(z) = q_0 + \frac{q_1 \ln(1+z)}{1 + n\ln(1+z)}$, from which the Hubble parameter $H(z)$ is derived analytically. This parametrization captures the transition from early deceleration to late-time acceleration, with a logarithmic correction governed by $n$ that distinguishes it from standard kinematic models. Model parameters $H_0$, $q_0$, $q_1$, and $n$ are constrained via MCMC using cosmic chronometer (CC) and Pantheon+SHOES datasets, individually and in combination. Across all dataset combinations, $q_0 < 0$, confirming ongoing accelerated expansion. The reconstructed $H(z)$ is consistent with $Λ$CDM at low redshifts, with mild deviations at higher redshifts. The $\{r, s\}$ statefinder parameters indicate that the model evolves smoothly, beginning with Chaplygin gas-type behaviour, crossing the $Λ$CDM fixed point, and settling into a quintessence-like phase at late times. The $Om(z)$ diagnostic reveals negative slopes throughout, indicating quintessence-like dark energy ($w > -1$). Present-day cosmic age estimates from the individual and combined datasets yield $t_0 \approx 13.7$ Gyr, in agreement with Planck 2018 constraints.

Classical carbon stars (atmospheric C/O >1) are asymptotic giant branch (AGB) stars that become carbon-rich through third dredge-up during the thermally pulsing AGB phase. However, carbon stars also occur among red giants and main-sequence stars, where the carbon is thought to originate from binary mass transfer from a former AGB companion. Using the all-sky catalog of G<16.5 mag Gaia DR3 carbon stars from Roulston et al. (2025), we investigate a uniform, high-confidence sample of carbon giants in the Milky Way, its globular clusters, and nearby Local Group galaxies. We identify 6937 carbon giants in the Large Magellanic Cloud, 2148 in the Small Magellanic Cloud, and 219 associated with the Sagittarius dwarf spheroidal, nearly quadrupling the previously known sample in the latter. We identify several candidate carbon symbiotic stars through their X-ray counterparts. The mean absolute C-AGB magnitude, $M^0_J=-6.30$ in the LMC and -6.15 in the SMC, agrees closely with the photometrically derived values of Ripoche et al. (2020), reinforcing the utility of carbon AGB stars as distance indicators. From 4276 Galactic carbon giants with $M_G<0$ and $|b|>5^\circ$, we measure a local disk space density of $n_0=11\pm0.5\times10^{-8},\mathrm{pc}^{-3}$ and a scale height of $H_z=257\pm4$ pc. Lower-luminosity carbon giants exhibit significantly larger Gaia DR3 RUWE values than C-AGB stars, providing strong evidence that most are extrinsic post-mass-transfer systems, likely evolved dwarf carbon stars. C-AGB stars are more tightly confined to the Galactic disk and are rare inside $R\lesssim7$ kpc, consistent with Galactic age and metallicity gradients, whereas the lower-luminosity carbon giants have a larger scale height and require an additional halo component.

The vast amounts of spectroscopic data for massive stars provided by previous and existing instruments on ground-based and space-based telescopes have saturated our capability to process them by human inspection routines. Consequently, there is a pressing need for fully automatic machine-assisted tools to help handle incoming data. To this end, we present the development of a massive star spectroscopic interactive database, Astro+. We aim to provide users with a reliable, versatile, and user-friendly platform that will be significant for understanding massive stars and set an important precedent for future open-access astrophysical research. This tool allows authorized users to upload their own spectra and, by using the fully automated tool HiLineThere, a Python-based program, it can homogeneously derive basic stellar parameters, such as v_rad, v sin i, Teff and log g for massive OB-type stars, using a solar-metallicity grid of FASTWIND models, and v_rad, [Fe/H], Teff and log g for red supergiant stars, in a completely autonomous way. Here we present the first results of the tool HiLineThere on optical spectra for OB-type stars and red supergiants. We compare the output of our analysis for OB-type stars with literature values for a large sample of well-studied objects, finding differences within the expected error ranges: Teff ~ 800 K, log g ~ 0.1 dex, and v sin i ~ 10 km/s. Preliminary tests on early-B stars also show consistent results during the transition to lower temperatures. For red supergiants, we find differences within 7 km/s in v_rad and ~300 K in Teff for two test samples.

We assess whether tabular foundation models can be used as off-the-shelf probabilistic photometric-redshift estimators for quasars in the 12-band S-PLUS DR6 survey, where colour-redshift degeneracies produce multi-modal posteriors and spectroscopic training sets are shifted relative to the photometric population. TabPFN 2.5, RealTabPFN 2.5, and TabICL are benchmarked against eight task-specific baselines, including linear conditional Gaussians, FlexZBoost, mixture-density networks, normalising flows, random forests, and gradient-boosted trees, with training sets from 500 to 121,626 quasars, using both density and point-prediction metrics, together with importance-weighted scores that approximate deployment on the photometric target sample. TabPFN 2.5 is best or statistically tied for best on all metrics except the unweighted CDE loss, on which the normalising flow is statistically tied and attains the lowest mean value; its largest gains occur for small training sets and in difficult regimes (very bright and faint sources, high redshift), while retaining near-nominal calibration under covariate shift. Its main practical cost is inference: with frozen weights, large support and target catalogues require substantial GPU/accelerator memory, and full-catalogue deployment may need support-set subsampling or distillation. SHAP attributions identify WISE W1/W2 as the strongest individual predictors, with UV and optical bands offering non-negligible refinements. We conclude that TabPFN 2.5 is a strong default for probabilistic quasar photo-z estimation, particularly when training data are limited or when calibration under covariate shift is critical.

Ultra-heavy asymmetric dark matter (DM) particles captured by compact stars can thermalize, self-gravitate, and collapse to form an endoparasitic black hole (EBH), whose subsequent growth may transmute the host star into a black hole. The continued existence of old millisecond pulsars (MSPs) and white dwarfs (WDs) thus places powerful constraints on the DM particle mass $m_χ$ and the DM-nucleon scattering cross-section $σ_{\rm nχ}$. We derive an analytical expression for the transmutation timescale by solving the EBH growth equation, consistently accounting for Bondi accretion of stellar matter, Hawking evaporation, and sustained DM feeding of the EBH in a steady-state capture regime. We also incorporate quantum effects in baryonic accretion when the hydrodynamic description breaks down, providing a unified treatment of EBH growth across both particle and fluid regimes. Adopting a physically transparent collapse criterion for fermionic and bosonic asymmetric DM, we compute EBH transmutation timescales for representative MSPs and WDs in environments with different DM densities. Although the physical ingredients are broadly similar to previous studies, this work derives updated constraints through a closed-form analytical treatment of EBH growth and an adopted prescription for the EBH formation timescale, yielding a lower critical EBH mass for sustained growth and revised transmutation timescales. Requiring the transmutation time to exceed $\sim 1$ Gyr for MSPs and $\sim 10$ Gyr for WDs, we derive revised constraints on $σ_{\rm nχ}$ over $m_χ\sim 10^{6}$--$10^{14}$ GeV, and show that EBHs with initial masses as small as $\sim 4\times10^{4}$ kg can undergo sustained growth, extending the region of DM parameter space probed by compact stars.

We present a model in which asymptotically de Sitter universes of various types, and de Sitter (dS) radii $R_n$, live in the interiors of black holes in a maximally entropic flat $p = ρ$ Friedmann-Robertson-Walker universe. These dS universes clearly have many quantum states. We argue that they decay and equilibrate with the maximal entropy universe on time scales of order $α_n R_n {\rm ln} (R_n /δ_n)$, where $α_n$ are model-dependent dimensionless constants and $δ_n$ are the initial distances between the shell, satisfying the Israel junction conditions, and the dS horizon. These are time-scales as viewed by a detector following a trajectory far from the would-be cosmological horizon. These times are all exponentially shorter than dS recurrence times, which have no meaning in this model. It is impossible for a detector inside one of the dS universes to determine whether it is actually part of such a structure. This model could be used as the basis for claiming that certain constants of nature or cosmological initial conditions were chosen to have mathematically unnatural values because other values could not lead to any form of intelligent life.

We study quasibound states of a massive neutral Dirac field in the Newman-Janis-generated rotating charged geometry used in Lorentz-violating Kalb-Ramond (KR) gravity. Rather than assuming that the Kerr separation survives the deformation, we first recast the metric in four-dimensional off-shell Carter form. The corresponding principal closed conformal Killing-Yano tensor then provides the hidden symmetry needed to separate the torsion-free, minimally coupled Dirac equation. We derive the horizon and large-radius boundary conditions, including the non-Minkowskian asymptotic normalization, and determine the complex spectrum from coupled angular and matrix radial continued fractions. The code reproduces the Kerr spectrum and is checked by truncation studies and independent two-sided radial integrations. In scans at fixed metric parameters, increasing the KR parameter moves most real frequencies toward the mass threshold and reduces most decay rates. These trends are not invariant, however, because the same variation changes both the asymptotic potential scale and the distance from extremality. A scan in which these two quantities are held fixed changes the absolute ground-state trend but preserves a reversal in the real-frequency ordering of the maximal-$m$, $j=3/2$, $\ell=1$ pair. The location of the crossing shifts with the normalization convention. Thus the level reordering is more robust than the individual monotonic trends in binding energy or lifetime within this background family.

Planet formation starts in disks that are still embedded within their natal envelopes. Here, we compile an extensive inventory of the chemical composition of the disk and envelope ($<$ 3500 au) around the Class 0 protostar L1527 IRS. Using all publicly available ALMA (Atacama Large Millimeter/submillimeter Array) data, we report the detection of 39 molecules, including isotopologues. Of these, 22 are different molecular species and 28 are reported here for the first time toward L1527 in ALMA observations. CH$_3$OH is the only complex organic molecule detected, while the hydrocarbon CH$_3$CCH is the largest molecule detected. Overall, only a few programs are sensitive enough to detect emission unambiguously originating from the disk based on the kinematics. Nitrogen-bearing molecules are predominantly detected on more extended scales, while hydrocarbons show a distinct tail roughly along the southeastern outflow cavity wall, probably due to a stronger UV field in the eastern outflow lobe. The L1527 IRS protostellar system is not rich in sulfur-bearing molecules, with only strong emission observed for CS and SO. Overall, the envelope appears dominated by a carbon-rich chemistry, which seems to transition into an oxygen-rich chemistry in the disk. We calculate column densities of all detected species, providing a starting point to quantify the chemical diversity among young disks and the chemical evolution of the planet-forming material.

Kurvature, a recently identified curvature invariant, has been argued to acquire superhorizon, or large-scale, white noise from hard-hard momentum coupling even when matter nonlinearities are small. If kurvature were related directly to cosmological curvature perturbations R through a Poisson equation, this white noise would cause an infrared-divergent variance sensitive to ultraviolet hard-mode physics. However, this relation does not generically hold. Kurvature is not intrinsic 3-curvature: on comoving slices it contains extrinsic-curvature terms, and intrinsic curvature is not related to R by a Poisson equation beyond linear order. We test this inference with second-order perturbation theory in radiation domination, relevant to CMB observables. Quadratic hard-hard composites do generate large-scale white noise in the kurvature density, but the Hamiltonian constraint separates it into intrinsic curvature and extrinsic shear, or equivalently density and expansion. Only the extrinsic terms carry the growing dimensionless kurvature density that mimics an ordinary density fluctuation above the horizon. The direct hard-hard curvature power is ultraviolet convergent, dominated by horizon-scale modes at evaluation, and leaves no IR relic in R from purely ultraviolet modes. By contrast, the Poisson construction of a curvature potential from kurvature is infrared divergent and cutoff sensitive; its white noise arises from extrinsic curvature associated with nonlinear acoustic beat modes in a radiation fluid.

One-loop divergences in classically conformal theory in curved spacetime is a nontrivial issue if the theory under consideration possesses gauge invariance. In this case, quantization involves introducing the gauge-fixing term and the action of ghosts, both of which are not conformal. The formal proof of the conformal invariant renormalizability in this situation, including interacting theories, has been given in the paper from 1984 by one of the present authors. Owing to BRST symmetry, the contributions of the gauge-fixing and ghost sectors to the conformal variation of the effective action cancel each other. This cancellation does not hold in the finite part of the one-loop and higher-loops effective action, that results in the anomaly. In this paper, we extend the early results on conformal matter fields in external gravitational field and apply them to conformal quantum gravity, including the case of conformal gravity coupled to other conformal matter fields. The gauge-fixing in the Weyl-squared gravity is more complicated, nevertheless, the proof of the one-loop conformal invariant renormalization using BRST symmetry is possible. As a preliminary to conformal quantum gravity, we also present a detailed general proof of conformal invariant one-loop divergences in the corresponding semiclassical theory.

I introduce the last crossing of the photon-counting barrier as a statistic for analytical models of cosmic reionization. Because ionizing galaxies are biased tracers of density and their photons propagate through gas of spatially varying opacity, the galaxy-IGM connection requires statistics beyond the global ionized fraction. The excursion-set model of Furlanetto et al. (2004) identifies the ionized-bubble scale around a point with the first crossing of a photon-counting barrier. I develop the last-crossing formalism and define the last-crossing scale, $R_\ell$, as the smallest scale on which the enclosed photon budget still ionizes the enclosed gas. I derive its distribution analytically. Using the empirical-barrier framework of Kaurov (2016) applied to CROC simulations, I measure both crossings in the simulated IGM. The last-crossing formalism separates externally ionized regions, whose photon-counting condition fails below $R_\ell$, from internally ionized regions whose trajectories remain above the barrier to the resolution scale. Resolved external regions are predominantly underdense, with larger $R_\ell$ selecting lower density and later reionization. At fixed local density, first-crossing scale, and reionization redshift, these regions show deficits in ionizing-luminosity and galaxy-number density at small radius relative to matched unresolved regions, and excesses in both at intermediate radius. Their combination of low gas density and a deficit of nearby sources suggests that Ly$α$ transmission spikes may preferentially arise in these regions: low density reduces the opacity, while sources on larger scales maintain the ionized state. The last-crossing picture connects the internal source geometry of ionized regions to a testable prediction for radial galaxy distributions around transmission-selected IGM locations.

The physical and chemical conditions of protoplanetary disks shape the properties of nascent planetary systems. The line ratios and relative abundances of the HCN-HNC isomer pair are well-suited for tracing these gas conditions, since isomer chemistry is linked to the underlying temperature, elemental abundances, and irradiation environment of the emitting gas. While HCN emits bright lines regularly observed in disks, the fainter HNC lines are targeted significantly less often, precluding our ability to calibrate the HNC-to-HCN ratio as a tracer of disk properties. Here, we present new Submillimeter Array observations of five transition disks around the T Tauri stars GM Aur, J1604, LkCa 15, GG Tau, and V4046 Sgr, covering the J=3-2 and J=4-3 lines of HCN and HNC. We detected at least one line of both HCN and HNC in each source and measured disk-integrated HNC-to-HCN flux and column density ratios of $\approx$0.1-0.7 and 0.1-0.4, respectively. For all sources, measured HNC fluxes exceed predictions from models of full (non-transition) disks by $\approx$3-10x, while HCN fluxes appear typical. The relative brightness of HNC vs. HCN in transition disks strongly suggests a link between the presence of a cavity and efficient HNC production. We corroborate this trend using chemical models of the DM Tau transition disk, showing HNC production and destruction are connected to the radiation environment. In our sample, disk-integrated HNC-to-HCN column density ratio shows no trend with disk gas temperature but positively correlates with disk mass due to increased HNC abundance in the larger reservoirs of cooler gas in more massive disks.