Devices based on the negative differential resistance effect in chromium doped V$_2$O$_3$ are considered to be promising as selector elements for use in emerging memory technologies, as well as for neuromorphic applications. It is shown by electrical measurements, that the switching effect is maintained for very thin films down to 5 nm, and even improved properties such as a low leakage current and an abrupt transition are observed. For these thicknesses, the behavior of crystalline and amorphous films becomes very similar; most strikingly, a forming step is required in both. Transmission electron microscopy reveals this to be likely due to a thin amorphous layer that forms at the interface to the TiN electrode. Elemental mapping further shows a complex distribution of the chromium dopants, as well as a diffusion of Ti into the layer from the electrode, which might be responsible for the improved properties.

Vortex pinning plays a crucial role in determining properties of type-II superconductors. For example, it governs the irreversible magnetic response as well as dissipation caused by vortex motion. Here, we study vortex pinning in the three-dimensional oxide superconductor Ba1-xKxBiO3 using ultra-high-resolution magneto-optical Kerr effect (MOKE) and detailed magnetization measurements. We find that the zero-field MOKE signal in the superconducting state exhibits a pronounced magnetic-history dependence. This behavior closely resembles the remanent magnetization caused by trapped vortices. Furthermore, we demonstrate that the observed evolution of the MOKE signals is well described by Bean's critical-state model for trapped vortices. Our results establish MOKE as a viable optical and mesoscopic probe of vortex pinning in type-II superconductors, providing a new complementary approach to investigate mixed-state phenomena. We also find that the training-field dependence of the MOKE is linear near zero training field, without any anomalies indicative of spontaneous time-reversal-symmetry breaking in an unconventional superconducting state. Our study defines a clear protocol to distinguish vortex-induced MOKE responses from those associated with a time-reversal-symmetry broken superconducting order parameter.

We study coherent manipulation of Majorana zero modes emerging in overscreened two-channel Kondo systems. Using compactified lattice models, we show that these interacting Kondo Majoranas support non-local qubits and admit teleportation, fusion, and braiding operations. In particular, we identify a distinction between non-topological and genuinely topological Y-junction geometries, the latter realizing a non-Abelian geometric holonomy. Our results establish a proof-of-principle route toward coherent control of non-Abelian anyons beyond conventional free-fermion platforms.

Metal phosphides have diverse bonding motifs and coordination environments, making them promising for optoelectronic and thermoelectric applications, but their chemical space remains underexplored. Here we report an AI-driven high-throughput discovery workflow that combines generative materials design, machine-learning interatomic potentials, and targeted density functional theory (DFT) calculations. ICSD-derived Wyckoff-site substitution and MatterGen-based conditional structure generation are used to expand the candidate space beyond existing phosphide databases. A domain-finetuned DPA3 machine-learning potential then enables efficient prescreening of thermodynamic and dynamical stability before DFT validation. This workflow identifies 3,574 previously unreported stable phosphide structures, including 196 semiconductors with HSE06 band gaps of 0-3.0 eV. By screening these new semiconductors together with experimentally known phosphide semiconductors, we identify 30 promising optoelectronic candidates and 26 promising thermoelectric candidates, including seven newly discovered optoelectronic materials and eight newly discovered thermoelectric materials. These results provide a candidate pool for experimental synthesis and show that combining generative AI with machine-learning interatomic potentials can accelerate the discovery of functional semiconductor materials.

Interpreting metal K-edge spectra of flexible photosensitizers requires a structural model that separates electronic signatures from thermal motion, solvent disorder, and crystal-packing effects. We combine Fe K-edge X-ray absorption measurements with second-generation Car--Parrinello ab initio molecular dynamics and all-electron Gaussian and augmented-plane-wave simulations for an iron(II) N-heterocyclic carbene photosensitizer in acetonitrile solution and in the crystalline phase. Ensemble-averaged spectra reproduce the main near-edge features in both environments and preserve the experimentally observed similarity of the first Fe coordination shell upon dissolution. Comparison with radial distributions extracted from extended fine-structure measurements validates the Fe--N and Fe--C coordination shells sampled by the trajectories, while element-resolved pair distributions explain why higher-shell experimental contrast is rapidly lost. The same dynamical ensembles reveal a broad out-of-plane distribution of the terpyridine nitrogen atom and a nearly octahedral distribution of the Fe-centered coordination planes. The results show that finite-temperature X-ray absorption simulations can provide a compact structural-dynamics picture of molecular transition metal photosensitizers by linking local spectra, solvent-phase ligand motion, and medium-range structural disorder within one trajectory-based description.

Machine learning models for materials property prediction increasingly rely on representations learned end-to-end from large density-functional-theory databases, limiting their applicability when only scarce experimental data are available. Domain-knowledge-driven representations precomputed from crystal structures alone offer a data-efficient, interpretable alternative, but existing approaches capture at most composition or bonding connectivity and discard local structural geometry. Here, we present Graphlet-MP, a database of graphlet histogram representations for 149,082 inorganic crystals from the Materials Project (MP). Seventy-nine distributions describe each material over three hierarchical graphlet orders: atomic sites, bonded pairs, and bond-angle triplets, extracted via screened Voronoi tessellation from the crystallographic information file. We provide a complete technical specification of the representation, an Earth Mover's Distance metric for comparing materials in this space, and the full precomputed database. An accompanying open-source codebase enables users to generate graphlet histograms for arbitrary crystal structures, including experimentally determined ones, and to extend the database to new materials or target properties.

Understanding how hydrostatic pressure modifies interlayer interactions and competing ionic configurations is essential for controlling the emergent functional properties of layered quantum materials. Here, using first-principles density-functional theory calculations, we investigate the pressure-dependent structural, mechanical, electronic, and optical properties of three competing LiInP2S6 polymorphs: the monoclinic C2/c phase and the trigonal P-31c phase in both in-layer and in-gap configurations. Our results reveal a pressure-induced structural phase transition from the monoclinic ground-state C2/c phase to a trigonal P-31c in-layer phase at ~0.38 GPa, driven by enhanced interlayer coupling and anisotropic lattice compression. In contrast, the trigonal P-31c in-gap phase remains energetically unfavorable due to its stronger interlayer ionic interactions and reduced compressibility. All phases remain mechanically stable under compression (0-26 GPa) and exhibit enhanced mechanical rigidity, elastic wave velocities, and Debye temperatures with increasing pressure. Remarkably, the electronic and optical properties within each phase remain highly robust under pressure, with only moderate changes in the band gap and optical absorption edge (UV-Visible range) under pressure; however, substantial modifications emerge across the pressure-induced structural phase transition. These findings establish LiInP2S6 as a pressure sensitive ionic-vdW material in which subtle changes in interlayer interactions govern structural stability and functional properties.

The thiospinel compound CuCo$_2$S$_4$ provides an attractive platform for exploring superconductivity in transition-metal chalcogenide spinels. Here, we report the first microscopic investigation of the superconducting state in CuCo$_2$S$_4$ using muon spin rotation and relaxation ($μ$SR) measurements, complemented by magnetization and heat-capacity experiments. The temperature dependence of the superconducting depolarization rate obtained from transverse-field $μ$SR measurements indicates a fully gapped superconducting order parameter. The extracted gap ratio $2Δ(0)/(k_{\mathrm{B}}T_\mathrm{SC}) = 3.95(2)$ exceeds the BCS weak-coupling value of 3.53, placing CuCo$_2$S$_4$ in the intermediate electron-phonon coupling regime. Zero-field $μ$SR measurements were performed to probe possible time-reversal symmetry breaking (TRSB) in the superconducting state. Within the experimental resolution, no additional spontaneous internal magnetic fields are observed below $T_c$. However, due to the presence of a ferromagnetic impurity phase and the associated fast-relaxing signal component, the sensitivity of the present measurements to weak spontaneous fields is reduced. Consequently, while no evidence for TRSB is detected, its existence cannot be definitively ruled out. Overall, our combined thermodynamic and $μ$SR results demonstrate that CuCo$_2$S$_4$ exhibits a fully gapped superconducting state with intermediate coupling strength, consistent with conventional $s$-wave superconductivity in this cobalt-based thiospinel system.

Active particles from bacteria to synthetic microswimmers often navigate viscoelastic media with complex relaxation dynamics. The classical active Brownian model that assumes instantaneous friction is clearly not applicable to describe such motility, while the non-Markovian processes combined with viscoelasticity are relatively unexplored. Here, we develop an analytical theory for an active particle in a power-law viscoelastic medium by solving coupled non-Markovian generalized Langevin equations for translational and rotational degrees of freedom. The viscoelastic memory results in novel phenomena such as fractional short-time transport, enhanced long-time persistence, and de-correlation of the instantaneous force and the swimmer orientation. We demonstrate that the memory kernel controls the anomalous scaling exponents, while the activity determines the crossover between sub-diffusive, ballistic and diffusive regimes. Our work provides a framework for theoretical description of biological and synthetic micro swimmers in complex biological and polymeric environments.

Modification of superconductor-dielectric interfaces is known to strongly impact coherence times of superconducting quantum devices. This relationship is thought to arise from differences in the concentration of "two-level system" defects in the disordered dielectrics and superconductor-dielectric interfaces; these defects couple to electromagnetic modes in the device and cause dissipation. Zirconium oxide barrier layers on niobium have emerged as a promising pathway to low-loss interfaces in recent years, evidently due to the crystalline nature of these layers in comparison to the amorphous niobium native oxide. We explain the unique ability of zirconium oxide to form a crystalline layer, to maintain a sharp interface with metallic niobium, and to prevent niobium oxide re-growth in terms of the chemical properties of ZrO$_2$ and the Nb-Zr-O ternary system. We demonstrate a new method to grow air-stable zirconium oxide layers on niobium with a higher level of crystallinity and a sharper oxide-metal interface than previously shown, and provide the first comprehensive microscopic analysis of ZrO$_2$ capping layer properties. These developments pave the way toward vital performance advances in superconducting quantum devices.

Point defects in crystalline materials play a central role in determining electronic, optical, and magnetic properties. However, systematic exploration of defect configurations remains computationally expensive because large supercell calculations are required to approximate isolated defects under periodic boundary conditions. We present a unit-cell-based tight-binding protocol that enables rapid pre-screening of substitutional defects. The protocol extracts Wannier tight-binding Hamiltonians from small, fully relaxed unit cells of the host and defect-like systems, replicates the host Hamiltonian to construct a supercell model, and introduces the defect by modifying only the on-site energies at the substitution site while leaving the hopping parameters unchanged. We validate the protocol across three diverse systems: isostructural substitutional defects in transition-metal dichalcogenides (M$_\mathrm{Mo}$ MoS$_2$, M = Ce, Zr, Nb, Tc, and Ru), symmetry-breaking carbon substitutions in hexagonal boron nitride (C$_\mathrm{B}$C$_\mathrm{N}$ h-BN), and nitrogen-vacancy (NV$^-$) centers in diamond. These case studies span two-dimensional and three-dimensional hosts, simple substitutions, and substitution-vacancy complexes. In all cases, the protocol successfully captures the number of in-gap states, their degeneracies, and their shallow or deep character relative to host band edges, despite some quantitative deviations in absolute energy positions. We further identify limitations for vacancies of highly electronegative atoms and for charge-state or spin-polarization effects, both of which involve self-consistent charge redistribution not captured by the protocol.

We investigate the thermodynamic properties of elemental cerium by assessing the crucial role of phonon free energy within the framework of dynamical mean-field theory (DMFT). While conventional density functional theory (DFT) often fails to capture the intricate energy landscape of $f$-electron materials, our approach integrates many-body electronic correlations with lattice dynamics to achieve a more rigorous description of the equation of state. We calculate the total energy as a function of the lattice constant at both the DFT and DFT+DMFT levels, subsequently incorporating the vibrational free energy derived from the phonon density of states. Our findings reveal that electronic renormalisation of the force constants significantly alters the phonon spectra, particularly in the strongly correlated $γ$-phase. By applying these phonon corrections to the energy profiles, we observe a substantial refinement in the predicted equilibrium volumes. Using principal-component-based machine learning, we interpolate phonon dispersions continuously from a finite set of first-principles calculations and compare them to experiment, finding significantly closer agreement compared to conventional DFT and DFT+U calculations that neglect dynamical many-body correlations. This study underlines the necessity of accounting for both electronic and vibrational entropy when evaluating the phase stability and structural transitions of lanthanide systems under varying pressures and temperatures.

Single-molecule toroics (SMTs) offer a unique platform for next-generation quantum devices utilizing head-to-tail spin alignments in the compounds. Presence of toroidal moments in SMTs has been essentially based on magnetometry and ab initio calculations. Here, we report observation and probe of the toroidal moment in [Dy3(OH)(teaH2)3(paa)3]Cl(OMe) [teaH3: triethanolamine; paaH: N-(2-pyridyl)-acetoacetamide] from mapping of Dy3+ magnetic susceptibility tensors by polarized neutron diffraction (PND). Neutron diffraction under variable magnetic fields demonstrates field-induced magnetization along the c-axis with toroidal moments anti-parallelly stacked, providing definite proof of the toroidal moment. Magnetometry studies confirm the toroidal ground state. For the first time, the combined use of PND, variable-field neutron diffraction, ab initio calculations, and magnetometry is introduced as a robust and quantitative methodology to probe molecular-scale toroidal magnetism. This integrated approach overcomes limitations of earlier indirect methods, establishes a benchmark framework for investigating SMTs, and provides valuable insights for the design of molecular quantum materials.

We study the dynamics of a spin-polarized wave packet in a disordered Rashba two-dimensional electron gas and identify a jittery quantum boomerang effect in which longitudinal and transverse motion return to the origin through fundamentally distinct mechanisms. Starting from an initial state with finite momentum along $x$ and spin polarized along $z$, we calculate the time evolution by combining a Chebyshev expansion of the time-evolution operator with a disorder ensemble average. In the weak-scattering regime, equations of motion derived from the quantum kinetic equation reproduce the numerical trends and show that impurity scattering acts as a viscous damping mechanism that suppresses the transient Zitterbewegung and drives the transverse displacement back to $y=0$ at long times. In contrast, the longitudinal dynamics show a Drude-like saturation at weak disorder. These results are consistent with the vanishing intrinsic spin Hall conductivity in the disordered Rashba model and with experimental observations of a transient intrinsic spin Hall effect in the time-domain. As disorder increases, the longitudinal dynamics evolve to a partial return toward the origin, which signals a transition from weak antilocalization to Anderson localization in 2D.

The topological properties of the Kitaev chain model with extended-range interactions are investigated, focusing on cases where the topological winding number is preserved. We assume that the pairing and hopping terms decay algebraically in space with exponents $α$ and $β$, respectively. We show that in the truncated-range scenario, there are as many distinct topological phases as the number of coupled neighboring sites. In addition, an explicit analytical formulation is provided to evaluate the topological invariant and the phase transitions that emerge in these systems. Besides the analytical description, we introduce a new physical insight into the topological excitations of the ground-state by measuring the spatial distribution of the edge modes with the Majorana average position. Taking the next-nearest neighbor Kitaev chains as a probe, various numerical calculations of Majorana edge states were performed in finite-size clusters to determine the sensitivity of the topological zero energy modes to the parameters of interest. The occupation of edge-to-edge non-local fermion states is computed and defined as an effective parity. Such an effective parity exhibits new interesting features beyond the energetic exchange from the ground-state fermion parity switches, which are related to the distribution of the respective edge modes. Our calculations show a direct correlation between the ground-state fermion parity and the edge occupation numbers, which are translated into localization and delocalization of the Majorana average position.

We generalize an influential framework for exactly solvable quantum dimer models with dual Ising gauge theory descriptions realizing the $\mathbb{Z}_{2}$ topological phase from trivalent to tetravalent parent lattices. The resulting quantum dimer models live on crossed-medial lattices and possess the remarkable feature of having crossed plaquettes, leading to transition graphs with generically intersecting loops. This non-planar structure runs counter to established templates for analytically tractable dimer liquids. As the simplest realization of the construction, we introduce an exactly solvable quantum dimer model on the checkerboard lattice that allows an exact mapping to the toric code, thus providing a particularly direct connection between the latter and Anderson's short range resonating valence bond paradigm. We further show that a corresponding crossed ruby lattice construction, dual to an Ising gauge theory on the kagome lattice, naturally falls within the same framework. More generally, the construction gives rise to a broad class of exactly solvable crossed-medial quantum dimer models and admits natural iteration, generating cascades of solvable $\mathbb{Z}_{2}$ topological dimer liquids beyond the standard planar setting. We furthermore extend Kasteleyn methods to the relevant non-planar graphs, enabling controlled wave-function deformations away from the commuting-projector points while retaining efficient evaluation of correlation functions.

Chiral materials with strong spin-orbit coupling offer a unique platform for exploring the interplay between topology, chirality, and quantum transport yet the quantum coherent regime in elemental tellurium nanostructures remains largely unexplored. Here we demonstrate phase-coherent quasi-ballistic transport, anisotropic Zeeman spectroscopy, and gate-tunable quantum dot formation in hydrothermally grown t-tellurium nanowires. Single nanowire field-effect transistors exhibit p-type transport with hole mobilities rising from approx. 80 cm2 V-1 s-1 at 210 K to approx. 190 cm2 V-1 s-1 at 1 K, consistent with a crossover from phonon-limited to Coulomb scattering dominated regimes near 50 K. Notably, devices segregate into two distinct regimes based on their room temperature two-terminal resistance : low-resistance devices (< 30 kOhm) exhibit Fabry-Perot interference, whereas high resistance devices (> 30 kOhm) display Coulomb-blockade behavior revealing a two-terminal resistance-driven transition between quasi-ballistic and strongly localized transport regimes. Zeeman spectroscopy in in-plane and out-of-plane magnetic fields yields highly anisotropic Lande g-factors (an in-plane gparallel = 1.18 and an out-of-plane gperp = 18.41) and directly resolves a spin-orbit energy gap DeltaSO = 0.864 meV from an avoided crossing. These results establish chiral tellurium nanowires as a versatile platform for gate-defined spin qubits exploiting large, tunable g-factors and for hybrid tellurium-superconductor architectures targeting Majorana zero modes in an elemental vdW system.

A distinctive feature of many quasiperiodic systems is the presence of critical states that are neither extended nor exponentially localized. We investigate the geometric effect on the superfluid weight in quasiperiodic systems with critical states at zero temperature. We employ both real-space and momentum-space approaches to superfluid weight in quasicrystals, which allows us to separate the conventional and quantum geometric contributions. We find that the superfluid weight is dominated by the geometric contribution in quasiperiodic systems with critical states. This finding reveals a fundamental interplay between superconductivity and critical states in quasicrystals.

We investigate the thermodynamic performance of quantum heat engines and refrigerators based on a two-spin system subject to a skew magnetic field. The working substance is described by an interacting spin model that incorporates both spin--spin coupling and anisotropy induced by a tilted magnetic field. We analyze and compare quantum Carnot and Otto cycles, showing that the Carnot cycle exhibits a universal, entropy-driven behavior with smooth phase boundaries, while the Otto cycle displays a much richer structure governed by the interplay between the energy spectrum and nonequilibrium population differences. In particular, we identify a crossover in both efficiency and coefficient of performance as a function of the interaction strength, which arises from the competition between the interaction energy scale and the magnetic field. We further demonstrate that the skew angle induces state hybridization, modifying both the energy levels and occupation probabilities. Our results highlight that interactions and anisotropy, when properly tuned, can enhance thermodynamic performance, and emphasize the importance of multi-level effects in the design of quantum thermal machines.

We present DarkAgents: a multi-agent system that leverages the reasoning and code-generation capabilities of large language models (LLMs), together with deterministic tested human-written code, to build orchestrated pipelines for theoretical astroparticle physics research. While related approaches have been proposed in collider physics and cosmology, DarkAgents targets the specific challenges of this domain, such as model building, complex pipeline computations, multiple constraints and assumption auditing. The framework can be powered by different agentic command-line tools, including Mistral's, Anthropic's, OpenAI's and local LLMs via Ollama. As first implementation, we apply DarkAgents to the study of cosmological first order transitions, starting from a classically scale-invariant particle-physics model and ending with the fit to the NANOGrav nanohertz gravitational-waves spectrum. DarkAgent-PT provides as output i) the best-fit values of model parameters, ii) their existing experimental and observational constraints, iii) an audit report of the assumptions and priors entering both i) and ii), of particular relevance for astroparticle physics. Our test runs identify inconsistencies in some fits in the literature and produce novel ones based on the dissipative bulk-flow GW template. The code is publicly available at https://github.com/PhysicsZandi/DarkAgents.

We present Ph-$Λ_{\rm s}$CDM, a phantom-scalar realization within General Relativity of the sign-switching cosmological-constant idea, $Λ_{\rm s}$CDM, in which a phantom scalar evolving on a bounded hyperbolic-tangent potential induces a smooth mirror AdS-to-dS transition in the late-time dark-energy density. The wrong-sign kinetic term, usually viewed as pathological, becomes the mechanism lifting the field from a negative- to a positive-energy vacuum-like regime. The construction also shows that the field can become repulsive while its energy density is still negative. The cosmology nevertheless remains controlled: total energy stays positive, the late-time attractor is de Sitter rather than a Big Rip, and the dynamics remain safely infrared. Ph-$Λ_{\rm s}$CDM thus offers a concrete late-time mechanism with the potential to address multiple cosmological tensions.

Amorphous tantala is an important optical material used in a number of high-precision optical applications, including gravitational wave interferometry. In this paper, we study in-situ the structural changes that occur in amorphous ion-beam sputtered coatings during an annealing treatment by means of a synchrotron radiation scattering experiment. The scattering signal is measured as a function of time on a large range of the Q-space. X-Ray diffraction and Rietveld analysis are used to study crystallization during the annealing treatment, whereas pair distribution function analysis allows to inspect the structural changes occurring during the amorphous to crystalline transition. Our findings indicate that several structural rearrangements occur in parallel, namely a first quick establishment of a backbone structure in the cationic substructure appearing on a rather extended range (up to 100 Angstrom), followed by a progressive rearrangement of the oxygen atoms environment which gradually increases the crystallinity of the structure.

The Expanding Box Model (EBM) has been widely employed to simulate multiscale plasma phenomena in the expanding solar wind by transforming the MHD equations to a co-moving, non-inertial frame. However, traditional formulations have suffered from historical ambiguity regarding the physical separation between the co-moving and inertial reference frames, primarily arising from a classical approximation of an invariant magnetic field between them. To resolve this inconsistency, we reformulate the EBM from first principles using a fully covariant approach. Here, we model the expanding solar wind frame as an anisotropic expanding spacetime metric, allowing us to incorporate radial acceleration profiles and differential transverse expansion, ensuring that all physical fields are correctly transformed by expansion. We demonstrate that the mathematical artifacts and structural asymmetries identified in previous EBM-MHD literature are direct consequences of neglecting the tensorial scaling of the magnetic field. Our covariant treatment eliminates these residues, restoring symmetry in the co-moving frame. Projecting our system back into the inertial frame recovers the established observational scaling and analogous physics, clarifies the mathematical distinction between local plasma dynamics and global expansion, and reveals the macroscopic anisotropy of the Parker spiral as a purely geometric projection. Furthermore, linear wave analysis demonstrates that macroscopic acceleration governs the evolution of Alfvén wave amplitude, acting either as geometric damping or as an energy source. Further, we write the EBM-MHD system using compressible Elsässer variables. This formulation provides a consistent and clean foundation for future numerical simulations of accelerating astrophysical plasmas.

This fifth release of the RIT public catalog of numerical relativity binary black hole waveforms http://ccrg.rit.edu/~RITCatalog introduces an additional 248 configurations, prioritizing 197 newly simulated eccentric orbits. This update brings the catalog to a total of 2129 cases. All waveforms are corrected for center-of-mass drift and extrapolated to future null infinity. To rigorously estimate waveform errors, we conduct multiple-resolution convergence studies on 10 eccentric simulations (up to 33 orbits to merger) using three global resolutions increasing by factors of 1.2, plus a comprehensive six-resolution study for a single 18-orbit configuration. We evaluate waveform accuracy by computing mismatches against theoretical infinite-resolution extrapolations. Additionally, we analyze the convergence properties of key physical observables: merger times, number of orbits, final masses, final spins, recoil velocities, and the peak amplitude, frequency, and luminosity of the gravitational radiation.

We investigate the crust-core transition in neutron stars using both thermodynamic and dynamical descriptions of the instability. In the thermodynamic approach, the transition is identified through the vanishing of a generalized incompressibility coefficient signaling the onset of a bulk spinodal instability. In contrast, the dynamical approach based on the relativistic random-phase approximation (RPA) incorporates Coulomb screening and finite-size effects that determine the instability at finite wavelength. Using a family of covariant energy density functionals spanning a broad range of symmetry-energy slopes, we show that the dynamical treatment systematically predicts lower transition densities and pressures compared to the thermodynamic approach. We further demonstrate that the RPA instability develops at a characteristic length scale set by the competition among bulk, Coulomb, and surface effects. Most importantly, we show that these differences propagate directly into neutron-star observables. Because the thermodynamic approach predicts larger transition pressures, it generates thicker crusts and significantly larger crustal fractions of the stellar moment of inertia than the dynamical-RPA framework -- with important implications for the interpretation of pulsar glitches and other crust-sensitive neutron-star observables.

For a system with a large number of identical Bosons, it is common to claim, often without any additional justifications, that, when the mean occupation number in a single particle state is sufficiently large, classical field description will be applicable. This is why e.g. for ultra-light dark matter, the classical field equations are used to compute its dynamics. In this work, we test the validity and robustness of this assumption based on the criterion $2 σ_φ< |\langle φ\rangle| $ for classical field behaviour and applying it to aribtrary quantum states. We find that an arbitrary state with large occupation number doesn't behave classically while imposing some restrictions on the state vectors can improve the classical behavior. Since coherent states are known to have quasi-classical behaviour, we also ask how much deviation from coherent state can spoil the classical behaviour. Based on this analysis, we find that it is the proximity of the state to a large occupation coherent state rather than large occupation number itself which ensures validity of classical description. Implications of this for ultra light dark matter are discussed.

Millicharged particles are well-motivated dark matter candidates that have been extensively investigated in terrestrial experiments. Recent studies proposed using the IceCube Neutrino Observatory to search for high-energy neutrinos produced by the capture and annihilation of millicharged dark matter in the Sun, deriving new constraints in the strong interaction regime where the millicharge is $q_χ\sim 10^{-3}$-$10^{-2}$, which extend to small fractional abundances where all existing constraints lose sensitivity. In this work, I point out that the lower energy threshold of water Cherenkov detectors makes Super-Kamiokande and the future Hyper-Kamiokande sensitive to neutrinos from the annihilation of lighter millicharged dark matter, complementing the high-mass reach of IceCube. I find that Super-Kamiokande can constrain previously unexplored parameter space at $m_χ=5$-28 GeV for dark matter fraction of $f_χ=10^{-4.5}$, while Hyper-Kamiokande can improve these constraints and will be sensitive to fractional abundances as small as $f_χ\simeq 5\times 10^{-6}$, nearly an order of magnitude below current IceCube limits.

High-frequency gravitational waves (HFGWs) in the MHz to GHz regime can convert into radio photons in the presence of astrophysical magnetic fields through the inverse Gertsenshtein effect. We show that existing radio telescopes like CHIME and FAST are excellent tools for detecting HFGW sources, significantly outperforming many existing experiments at detecting primordial black hole (PBH) mergers, the most realistic sources of transient HFGWs. Radio telescopes are also uniquely sensitive to sources of monochromatic HFGW emission, such as ultralight boson clouds formed through superradiance around PBHs, and are likely to have excellent sensitivity to generic sources of detectable HFGWs.

The generalized cosmological time (GCT) framework introduces a modified lapse function, N(t)\propto a^{b/4}, as a geometric extension of the standard FLRW description. Like other departures from $Λ$CDM, such constructions must remain compatible with the observed stability of local gravitational and laboratory physics. In scalar--tensor theories, this compatibility is usually achieved through dynamical screening mechanisms that suppress additional degrees of freedom in dense environments. In this work, we examine whether a locally static spacetime region can be consistently embedded within a cosmological background described by a time-dependent lapse. By embedding a static Schwarzschild interior into an expanding GCT--FLRW exterior, the Israel junction conditions are used to determine the class of background expansions that admit such a matching in the absence of a thin shell. The continuity of the extrinsic curvature yields a Friedmann-type relation that coincides with the GCT background equations of motion. This relation should be interpreted not as a new dynamical equation, but as a geometric consistency condition (GCC) associated with the matching of the two spacetime regions. In this sense, the junction does not introduce new dynamics, but provides a GCC under which a region with fixed local clocks can be embedded in a cosmological spacetime with an evolving lapse. Therefore, the analysis clarifies how locally static gravitational systems can remain compatible with a cosmological time normalization that differs from that of local proper time while preserving the standard description of local physics.

Recently, a chemically depleted young massive stellar population was identified using the spectroscopic catalogue of Gaia DR3. To explain its characteristics, a recent enhanced star formation event, via a third infall occurring within the last 2 Gyr, has been evoked. In this paper we reassess the low alpha sequence of massive stars identified in the Gaia spectroscopic catalog and investigate their presence in other Milky Way spectroscopic survey catalogs. We select massive sequence stars and RGB stars from the Gaia DR3 catalogue using the same filtering strategy adopted in previous chemical cartography studies. These samples are then cross matched with APOGEE DR17, GALAH DR4, and Gaia CNN to enable a detailed comparison of stellar parameters and alpha abundances. Stellar masses are estimated by projecting their atmospheric parameters and infrared magnitudes onto PARSEC isochrones. For the massive star sample, we find large discrepancies in stellar parameters and calcium abundances between Gaia DR3 and the three external surveys. The external catalogues do not show a low ca sequence but rather resemble those of thin disc RGB stars. Other alpha elements (si in APOGEE and GALAH, and mg in GALAH) also do not show depleted values. In APOGEE, however, massive sequence stars with metallicities above -0.5 dex display lower mg abundances. We attribute this to APOGEE's use of macroturbulence velocities calibrated solely on metallicity. Our analysis does not show any evidence for alpha element depletion in massive sequence stars. Alpha abundances of massive sequence stars derived from the Gaia RVS spectra should therefore be used with caution. Nevertheless, the previously proposed three infall chemical evolution models remain plausible: even without a chemically depleted young massive population, scenarios involving only mild dilution could still account for recent star formation episodes.