We investigate the behavior of curvature invariants for a large ensemble of neutron stars built with equations of state (EOSs) that satisfy constraints from nuclear theory and perturbative quantum chromodynamics (QCD), as well as measurements of neutron-star masses, radii, and gravitational waves from binary neutron-star mergers. Surprisingly, our analysis reveals that stars with negative Ricci scalar $\mathcal{R}$ are rather common and about $\sim 50\%$ of our EOSs produce one or more stars with Ricci curvature that is negative somewhere inside the star. The negative curvature is found mostly but not exclusively at the highest densities and pressures, and predominantly for stiff EOSs and for the most compact and most massive stars. Furthermore, we improve the quasiuniversal relation between the stellar gravitational mass $M$ and the baryonic mass $M_{\mathrm{b}}$, which allows us to express analytically one in terms of the other with a maximum variance of only $\sim 3\%$. Finally, using the relation between the Ricci scalar and the trace anomaly $\mathrm{\Delta }$, we determine the conditions under which $\mathrm{\Delta }$ vanishes or becomes negative in neutron stars.

The Higgsino-like neutralino is a compelling dark matter candidate motivated by both cosmology and naturalness considerations. While a pure Higgsino typically requires a mass of around 1.1 TeV to satisfy the observed thermal relic abundance, the presence of light sleptons can significantly alter this requirement. In this work, we revisit Higgsino dark matter within the minimal supersymmetric standard model, focusing on scenarios with slepton coannihilation. We find that the presence of nearly mass-degenerate sleptons in the thermal bath can allow the Higgsino mass to be as light as $\sim 400\mathrm{GeV}$ while satisfying relic density constraints. We explicitly contrast the impact of recent direct detection updates: the LZ-2022 limits raise this lower bound to approximately 450 GeV, while the stringent LZ-2024 constraints further shift the viable mass floor to $\sim 500\mathrm{GeV}$. Crucially, we demonstrate that the direct detection sensitivity is strongly dependent on the relative signs of the gaugino mass parameters $M_1$ and $M_2$. We find that scenarios with $M_1,M_2>0$ are fully excluded by LZ-2024. Conversely, configurations with opposite signs ($M_1/M_2<0$) remain broadly viable, as destructive interference in the neutralino-Higgs coupling efficiently suppresses the spin-independent cross section. Finally, we delineate the remaining viable parameter space for both the opposite-sign cases and the specific configurations with negative $M_1$ and $M_2$.

New, neutrinophilic mediators are one potential extension beyond the Standard Model of particle physics. Often, studies of a neutrinophilic mediator consist of searching for direct evidence of its production and/or its tree-level virtual effect for generating strong neutrino self-interaction. In this work, we focus instead on the fact that such new mediators also lead to deviations in neutrino-matter scattering via radiative corrections. With a mediator mass well below the electroweak scale, these effects are potentially observable in a variety of contexts, including coherent elastic neutrino-nucleus scattering, neutrino deeply inelastic scattering, and neutrino-electron scattering (e.g., at Borexino). Additionally, such effects lead to new contributions to the $Z$-boson decay width and to nonstandard neutrino interactions relevant for long-baseline oscillation experiments. We explore all of these scenarios in some depth, building on the rich phenomenology associated with neutrinophilic mediators.

Traditional seesaw mechanisms provide an elegant theoretical framework in explaining the tiny yet nonzero masses of neutrinos. Nevertheless, they face significant challenges in experimental searches, primarily because the energy scale associated with the seesaw mechanism is too high to be directly reached by terrestrial experiments. In this paper, we explore the gravitational waves (GWs) generated via graviton bremsstrahlung during the decay of seesaw particles in the early Universe. Specifically, we compute the GW spectrum resulting from the decay of the Higgs triplet within the type-II seesaw model. Our results demonstrate that the resulting GW spectrum depends sensitively on the mass of the Higgs triplet and its couplings to the Standard Model Higgs doublet and the left-handed lepton doublets. The detection of such a high-frequency GW background could offer a unique experimental window into the seesaw mechanism and provide indirect evidence for its validity.

We propose a novel and minimal setup where the observed baryon asymmetry of the Universe and neutrino oscillation data can be satisfied with only one right-handed neutrino and a second Higgs doublet with the latter being also responsible for driving cosmic inflation. While inflation is realized via nonminimal coupling of the Higgs to gravity, baryon asymmetry is generated via Affleck-Dine leptogenesis. Due to the presence of only two new fields beyond the standard model (BSM), the proposed setup remains very predictive with only a small allowed parameter space consistent with the PLANCK 2018 and ACT 2025 data simultaneously. The preferred mass spectrum of the BSM particles also keeps the detection prospects alive at terrestrial experiments.

We test the eigenstate thermalization hypothesis (ETH) in $1+1$-dimensional SU(2) lattice gauge theory (LGT) with one flavor of dynamical fermions. Using the loop-string-hadron framework of the LGT with a bosonic cutoff, we exactly diagonalize the Hamiltonian for finite size systems and calculate matrix elements (MEs) in the eigenbasis for both local and nonlocal operators. We analyze different indicators to identify the parameter space for quantum chaos at finite lattice sizes and investigate how the ETH behavior emerges in both the diagonal and off-diagonal MEs. Our investigations allow us to study various timescales of thermalization and the emergence of random matrix behavior, and highlight the interplays of the several diagnostics with each other. Furthermore, from the off-diagonal MEs, we extract a smooth function that is closely related to the spectral function for both local and nonlocal operators. We find numerical evidence of the spectral gap and the memory peak in the nonlocal operator case. Finally, we investigate aspects of subsystem ETH in the lattice gauge theory and identify certain features in the subsystem reduced density matrix that are unique to gauge theories.

Two-point correlation functions of systems with baryon number $B\in \{1,2,3,4\}$ are investigated using lattice quantum chromodynamics (QCD). In particular, the empirical distributions of importance-sampling Monte-Carlo samples of these correlation functions are examined as a function of the spacetime separation between the two points and the baryon number. While the exact forms of these distributions are not known for QCD, recent work has determined asymptotic expressions for analogous correlation function distributions in simpler theories such as scalar field theory and the disordered phase of the $O(N)$ model. The theoretical $O(N)$ model distributions are found to provide an accurate description of the empirical QCD distributions at zero momentum over a wide range of temporal separations for each baryon number when assessed with a range of different statistical tests. In particular, the behavior of the baryon number $B$ QCD correlation function at large temporal separation is well reproduced by the $O(N\sim 2/B)$ model distribution.

A crucial step in extracting physical predictions from lattice quantum chromodynamics (QCD) simulations is the scale setting, i.e., the determination of the lattice spacing ($a$) in physical units. Herein, the relative scale setting for different $\beta$’s is discussed, using the Landau gauge gluon propagator computed with large statistical ensembles. After setting the relative scales, finite size effects are observed in the ultraviolet regime and handled in an effective description, inspired in perturbation theory. The new devised procedure is efficient in handling the finite size effects, linking the lattice simulations with continuum perturbation theory for the high momenta regime. Furthermore, the procedure can be extended to handle other Green’s functions computed within lattice QCD simulations.

We study the radiative decays $D_{s1}(2460)\to \gamma D_{s0}^{*}(2317)$ and $D_{s1}(2460)\to \gamma D^0{K}^{+}/\gamma D^{+}{K}^0$ and argue them to constitute a paradigmatic case of reactions sensitive to the short-range component of the decaying meson wave function that can, in principle, be quantified in a model-independent way employing experimental data. We demonstrate how a simultaneous measurement of the above radiative decay widths, or at least a constraint on the ratio of the corresponding branching fractions, can allow one to probe the nature of the $D_{s0}^{*}(2317)$ and $D_{s1}(2460)$ mesons.

We present results of the search for sub-GeV dark matter interaction with electrons in the NaI(Tl) crystals of the COSINE-100 experiment. The two benchmark scenarios of a heavy and a light vector boson as mediator of the interaction were studied. We found no excess events over the expected background in a dataset of 2.82 years, with a total exposure of $172.9\mathrm{kg}-\mathrm{year}$. The derived 90% confidence level upper limits exclude a dark matter (DM)-electron scattering cross section above $6.4\times {10}^{-33}{\mathrm{cm}}^2$ for a DM mass of 0.25 GeV, assuming a light mediator; and above $3.4\times {10}^{-37}{\mathrm{cm}}^2$ for a 0.4 GeV DM, assuming a heavy mediator, and represent the most stringent constraints for a NaI(Tl) target to date. We also briefly discuss a planned analysis using an annual modulation method below the current 0.7 keV threshold of COSINE-100, down to few photoelectrons yield.

We report on a broadband search for axionlike particle (ALP) interactions using a radio-frequency operated ${}^{87}\mathrm{Rb}$ atomic magnetometer. The instrument provides wide spectral coverage and sensitivity to an oscillating pseudomagnetic field that may be generated by the gradient coupling of the ALP field to the constituent fermions of atoms. We search for an ALP-gradient signature in the mass range $2.40\times {10}^{-10}\mathrm{eV}/c^2–2.11\times {10}^{-9}\mathrm{eV}/c^2$. No statistically significant signatures of an oscillating magnetic field are observed, and we derive upper limits on the corresponding ALP-proton, -neutron, and -electron couplings, $g_{\alpha pp}$, $g_{\alpha nn}$, and $g_{\alpha ee}$, respectively. The result on $g_{\alpha pp}$ improves over previous laboratory searches, while the limits on $g_{\alpha nn}$ and $g_{\alpha ee}$ complement earlier laboratory searches and astrophysical bounds. The work extends searches for ALP-fermion interactions into a mass region largely unexplored in a dark matter context, demonstrating the potential of our method for broadband axionlike particle searches targeting the Galactic dark matter halo.

The recent developments in the study of topological multiboundary entanglement in the context of 3D Chern-Simons theory (with gauge group $G$ and level $k$) suggest a strong interplay between entanglement measures and number theory. The purpose of this note is twofold. First, we introduce a $q$-deformed version of the Witten zeta function using the Chern-Simons theory at level $k$. We analyze the large $k$ limit of this function and show that it converges to an integer multiple of the classical Witten zeta function of $G$, where the integer multiple is precisely the order of the center of the group. This analysis provides an alternative way to compute the classical zeta functions, and we present some examples. Next, we study the quantum state associated with the $S^3$ complement of torus links of type $T_{p,p}$ and show that we can write the Rényi entropies at finite $k$ in terms of $q$-deformed Witten zeta functions. Using our first result, we obtain the $k\to \infty$ limit of the Rényi entropies and find that the entropies converge to finite values, which can be written in terms of the classical Witten zeta functions evaluated at positive integers. Since Witten zeta functions naturally appear in the symplectic volumes of moduli spaces of flat connections on Riemann surfaces, we give a geometric interpretation of the $k\to \infty$ limit of the Rényi and entanglement entropies in terms of these volumes. The results of this paper reveal an intriguing connection between topological entanglement, number-theoretic structures arising from Witten zeta functions, and the geometry of moduli spaces.

We analyze the gauge dependence of the effective action in an interacting quantum theory of gravitational and matter fields. An explicit off-shell result is obtained in a general background gauge at one-loop order, which reduces in a particular gauge to the effective action found by ’t Hooft and Veltman [Ann. Inst. Henri Poincare Phys. Theor. A 20, 9 (1974)]. We confirm the validity of DeWitt-Kallosh theorem, which implies that the on-shell effective action should be independent of the gauge-fixing parameter. We employ this theorem to expose the nonrenormalizability of the theory in a general background gauge.

This paper investigates entanglement entropy in $3+1$ dimensional Lorentzian covariant loop quantum gravity (LQG). We compute the entanglement entropy for a spatial region from states dynamically generated by a spinfoam path integral that sums over a family of two-complexes. The resulting entropy exhibits a geometric area law, $S\simeq \beta a$, where the area $a$ of the entangling surface is determined by the LQG area spectrum and the leading coefficient $\beta >0$ is independent of the underlying two-complexes. By relating the coupling constant of the sum over two-complexes to the Barbero-Immirzi parameter $\gamma$, we reproduce the Bekenstein-Hawking formula for the range $0<\gamma \lesssim 1/2$. This work provides a Lorentzian path integral approach to gravitational entropy without the need for contour prescriptions.

We study the covariant diffusion and drift of massless particles on the light cone within the context of quantum gravity phenomenology. Unlike modified dispersion relations that violate Lorentz invariance and grow with frequency, this model introduces a stochastic correction to the massless geodesic equation while preserving Lorentz invariance, and is dominant at lower frequencies due to the larger spacetime support of long-wavelength modes. The effect is phenomenologically described by just two diffusion and drift parameters, ${\kappa }_1$ and ${\kappa }_2$, whose values are already constrained by measurements of the CMB blackbody spectrum. We show that a direct measurement and characterization of a gravitational wave (GW) background frequency spectrum can improve bounds on these diffusion and drift parameters by over 12 orders of magnitude compared to those from the CMB. In particular, we find that detecting a GW background sourced by realistic models of first-order phase transitions or primordial black holes with the Laser Interferometer Space Antenna can constrain the parameters down to a value of ${\kappa }_1,{\kappa }_2\lesssim {10}^{-56}\mathrm{kg}{\mathrm{m}}^2{\mathrm{s}}^{-3}$.

Accurate modeling of extreme mass-ratio inspirals (EMRIs) is essential for extracting reliable information from future space-based gravitational wave observatories. Fast waveform generation frameworks adopt an offline/online architecture, where expensive relativistic computations (e.g., self-force and black hole perturbation theory) are performed offline, and waveforms are generated rapidly online via interpolation across a multidimensional parameter space. In this work, we investigate potential sources of error that result in systematic bias in these relativistic waveform models, focusing on radiation-reaction fluxes. Two key sources of systematics are identified: (i) the intrinsic inaccuracy of the flux data, for which we focus on the truncation of the multipolar mode sum, and (ii) interpolation errors from transitioning to the online stage. We quantify the impact of mode-sum truncation and analyze interpolation errors by using various grid structures and interpolation schemes. For circular orbits in Kerr spacetime with spins larger than $a\ge 0.9$, we find that ${\ell }_{\max }\ge 30$ is required for the necessary accuracy. We also develop an efficient Chebyshev interpolation scheme, achieving the desired accuracy level with significantly fewer grid points compared to spline-based methods. For circular orbits in Kerr spacetimes, we demonstrate via Bayesian studies that interpolating the flux to a maximum global relative error that is equal to the small mass ratio is sufficient for parameter estimation purposes. For 4-year long quasicircular EMRI signals with $\mathrm{SNRs}=\mathcal{O}(100)$ and mass-ratios ${10}^{-4}-{10}^{-6}$, a global relative error of ${10}^{-6}$ yields mismatches $<{10}^{-3}$ and negligible parameter estimation biases.

We develop a unified framework for analyzing black hole thermodynamics and spacetime structure in Einstein gravity coupled to causal nonlinear electrodynamics in asymptotically anti–de Sitter (AdS) backgrounds. The electromagnetic sector is governed by a generalized nonlinear electrodynamics Lagrangian obtained from a root-$T\overline{T}$ deformation constructed via the Courant-Hilbert approach, ensuring both duality invariance and causal propagation. This theory contains modified Maxwell (ModMax), generalized Born-Infeld, and self-dual logarithmic electrodynamics as continuous limits. Within this framework we obtain exact charged AdS black hole solutions and perform a detailed study of their thermodynamic properties, including mass, temperature, entropy, and free energy. The resulting phase structure exhibits van der Waals–type transitions between small and large black holes and features a characteristic swallowtail in the free energy at the critical point. We further investigate the internal geometry, showing that the nature of the central singularity is determined by the matter fields that source the spacetime. An analysis of the Kretschmann scalar reveals how mass and electric charge jointly govern curvature divergence in ModMax black holes. We derive an explicit charge-to-mass bound within a causal logarithmic electrodynamic theory. This extends the finite self-energy property of the point charge beyond the standard Born-Infeld model. This bound cleanly distinguishes black holes from naked singularities, showing that naked singularities occur precisely when the mass parameter is smaller than the electromagnetic self-energy of the point charge. This provides a clear energetic criterion for horizon formation in the absence of a Cauchy horizon.

We suggest a formation scenario of black holes with intermediate mass $\sim {10}^3{M}_{\odot }$, by postrecombination Bondi-Hoyle-Lyttleton accretion into ultradense dark matter halos (UDMHs) of $\sim {10}^5{M}_{\odot }$, which have formed around the recombination epoch. Such UDMHs can result from rare curvature fluctuations on small scales whose amplitude is still well below the current Cosmic Microwave Background (CMB) spectral distortion limits. Gas accreted by the UDMH is heated to virial temperatures above which atomic cooling is efficient, cools rapidly to about $\sim 8000\mathrm{K}$, and collapses on the free fall time of few ${10}^4\mathrm{yr}$ to the halo core, until supported by rotation. Further fragmentation due to molecular cooling is prevented by the suppression of $H_2$ molecule formation by the CMB photons at redshifts $z>200–400$. We find that the rotationally supported gas disk will be compact and massive enough to undergo self-gravitational instability in some cases, plausibly where accretion is into a nearly spherical UDMH which has formed from a rare peak in the density field. This results in a further, rapid transfer of mass inward due to viscous forces and gravitational torques leading to the formation of a supermassive star and/or black hole of about ${10}^3{M}_{\odot }$ at redshifts of a few hundred. Such intermediate mass black holes formed at high redshifts can have a large-enough abundance to seed the first super massive black holes and help explain the abundance of active galaxies detected now at increasingly larger redshifts by the James Webb Space Telescope.

The indirect ground-based observations of cosmic rays through extensive air showers in modern experiments typically involve the use of Monte Carlo simulations to determine the characteristics of the primary particles. These simulations necessitate assumptions about particle interactions at energies that have not yet been experimentally probed, which introduces systematic uncertainties in key observables, particularly the number of muons. Current research on this uncertainty primarily focuses on hadronic interaction models, the dominant source of muon production. This study presents an approach that takes into account another significant mechanism for muon generation: photonuclear reactions. A robust heuristic technique has been developed to estimate the contribution of these interactions to the total number of muons over a wide range of extensive air shower parameters (including primary particle type, energy, and slant atmospheric depth) and photonuclear interaction models, with an absolute percentage error on the order of 10% in the estimated number of muons. Furthermore, several potential applications of the suggested method in relation to modern challenges in extensive air shower physics are discussed.

We investigate self-bound quark stars in a flavor-dependent quark-mass density-dependent model with an excluded-volume correction. We chart the parameter space at zero pressure to identify self-bound regimes, including parametrizations in which self-bound two-flavor matter undergoes a genuine first-order $ud\to uds$ transition at finite pressure. We construct cold, $\beta$-equilibrated stellar sequences and compute the corresponding global properties (mass-radius relation, tidal deformability, and moment of inertia). For a wide region of the model parameter space, we find that the onset of a $uds$ core occurs before the maximum-mass configuration is reached, yielding self-bound hybrid stars that follow the typical strange-quark-star sequence morphology but develop a characteristic kink at $p_c=p_{\mathrm{tr}}$ along the stellar curves. The excluded-volume parameter $\kappa$ controls the stiffness of the equation of state and thus masses, radii, tidal deformabilities, and moments of inertia; intermediate repulsion typically reconciles $M_{\max }\gtrsim 2M_{\odot }$ with current astrophysical constraints. We further identify two equation-of-state insensitive trends—dimensionless moment of inertia versus compactness and gravitational versus baryonic compactness. These results provide model-guided priors and tools for discriminating between hadronic and self-bound equations of state with multimessenger data.