We introduce a minimal two-parameter formulation of the dark energy (DE) density evolution normalized to its present-day value, $f_{\mathrm{DE}}(z)\equiv {\rho }_{\mathrm{DE}}(z)/{\rho }_{\mathrm{DE},0}$, in terms of $f_p\equiv f_{\mathrm{DE}}(z_p)$ and the DE equation of state $w_p\equiv w(z_p)$, at a pivot redshift $z_p$. This provides an alternative framework for assessing the evidence for evolving DE, complementary to the established Chevallier-Polarski-Linder (CPL) parametrization of the DE equation of state in terms of $w_0$ and $w_a$. By parametrizing the DE density directly, the $(w_p,f_p)$ formulation avoids the approximate degeneracies intrinsic to the $(w_0,w_a)$ basis—in particular the weak sensitivity of the expansion history to $w_a$—while reproducing the background evolution of representative thawing quintessence models with equivalent accuracy. Confronting it with the latest baryon acoustic oscillation (BAO) measurements from DESI, a prior on early-Universe parameters from Planck cosmic microwave background (CMB) observations, and Type Ia supernovae (SNe) data, we find that the $w_p$ and $f_p$ parameters are both tightly constrained and sensitive to distinct subsets of the data. Specifically, $w_p$ is measured to percent-level precision by BAO and CMB alone, while $f_p$ is pinned down by the independent matter density constraint that only SNe provide. Including the Pantheon+ SNe sample, we obtain $w_p=-1.04\pm 0.04$ and $f_p=1.07\pm 0.04$, with similar results when using the DESY5 SNe sample. The frequentist preference for evolving DE over $\mathrm{\Lambda }\mathrm{CDM}$ remains below $3\sigma$ across all dataset combinations, comparable to that obtained with CPL. Notably, the proximity of both $w_p$ and $f_p$ to their cosmological constant values of $(-1,1)$—precisely at the epoch where the data are most sensitive—deepens the coincidence previously identified in the CPL framework, reinforcing the case for caution in interpreting the current evidence for dynamical DE.

The Galactic Center is potentially hosting the largest indirect signal from particle dark matter (DM), which in many well-motivated models would produce gamma rays as their final states. However, this region has often been dismissed for DM studies because of the evidence for an unexpected gamma-ray component over astrophysical backgrounds at GeV energies, firstly discovered in the data of the Fermi Large Area Telescope (LAT), the so-called Galactic Center excess (GCE). While this was initially considered to hint at GeV thermal relics, recent work supports a GCE interpretation in terms of a stellar population of millisecond pulsarlike sources in the Galactic bulge. Building on this preference, we reevaluate the Galactic Center as a powerful target for indirect DM searches via gamma rays. This is achieved by combining adaptive template fitting and photon-count statistical methods to assess the role of subthreshold point sources in the observed Fermi-LAT gamma-ray counts while minimizing the mismodeling of Galactic diffuse-emission backgrounds. In a fully self-consistent way, the gamma-ray data are fitted with a mixed model comprising a DM signal and a stellar bulge, both potentially contributing to the GCE. The space left for signals from weak-scale DM particle annihilations is quantified by extracting 95% confidence level upper limits on the annihilation cross section, which, depending on the DM density profile, result in stringent limits for masses $\lesssim 300\mathrm{GeV}$. The robustness of our results is supported by tests on simulated data.

The postmerger phase of binary neutron star (BNS) mergers encodes valuable information about the equation of state (EOS) of supranuclear matter. Extracting this information from the analysis of the postmerger waveforms remains challenging due to the high-frequency limitations of current detectors. Future third-generation observatories, such as the Einstein Telescope (ET) and NEMO, will have the sensitivity required to resolve post-merger signals with high fidelity. In this work, we apply clawdia, our recently developed sparse dictionary learning (SDL) framework, to classify different EOS models using the merger and postmerger gravitational-wave emission of simulated BNS mergers available in the core database. Our dataset comprises five EOS models representative of a broad range of neutron star properties. The SDL framework is optimized under realistic detection conditions by injecting signals into simulated noise matching the sensitivity curves of ET and NEMO. Our results show that classification is primarily driven by the dominant postmerger frequency, $f_2$, which encodes EOS-dependent information. At a modest signal-to-noise ratio of 5, our method achieves $F_1$ scores of 0.76 for ET and 0.70 for NEMO, with performance improving for higher signal-to-noise ratios. The reliability and generalization capabilities of the model are assessed with additional tests, including the classification of an EOS not included in the training dataset and the analysis of detector-specific biases.

Nonradial oscillations of dark matter admixed neutron stars offer a powerful probe of stellar structure and relativistic gravity, but when the ordinary and dark matter components are modeled as dynamically distinct fluids, their consistent description requires a two-fluid treatment that retains the dynamical response of both components and their coupling to spacetime. The system considered here corresponds to the noninteracting limit of the established general relativistic formalism for polar perturbations of two-fluid stars, but is formulated directly for independently conserved perfect-fluid components that interact only through gravity, without entrainment or direct microphysical coupling. Within this formulation, we present the coupled linear perturbation equations for the spacetime metric and both fluid components, together with the central regularity conditions, the boundary conditions at the individual fluid surfaces, and the matching to the exterior vacuum spacetime required to determine the polar mode spectrum. We implement this system numerically for mirror dark matter admixed neutron stars, describing both components with the QHC21-BT equation of state, and compute representative polar mode spectra. The resulting spectra contain distinct fundamental ($\mathsf{f}$) and pressure ($\mathsf{p}$) mode branches with dominant inner- or outer-fluid character, which we identify from the associated eigenfunctions and their radial node structure. We find that the additional gravitationally coupled fluid shifts the ordinary-matter-led $\mathsf{f}$-mode branch and that the equation-of-state-insensitive universal relation between the mass-scaled $\mathsf{f}$-mode frequency and compactness known for single-fluid neutron stars is not preserved in the same form. These results provide a fully general relativistic characterization of the polar mode spectrum of mirror dark matter admixed neutron stars and illustrate the asteroseismic signatures introduced by an additional gravitationally coupled fluid component.

We present results from the search for an isotropic gravitational-wave background using Advanced LIGO and Advanced Virgo data from O1 through O4a, the first part of the fourth observing run. This background is the accumulated signal from unresolved sources throughout cosmic history and encodes information about the merger history of compact binaries throughout the Universe, as well as exotic physics and potentially primordial processes from the early cosmos. Our cross-correlation analysis reveals no statistically significant background signal, enabling us to constrain several theoretical scenarios. For compact binary coalescences which approximately follow a $2/3$ power-law spectrum, we constrain the fractional energy density to ${\mathrm{\Omega }}_{\mathrm{GW}}(25\mathrm{Hz})\le 2.0\times {10}^{-9}$ (95% credibility), a factor of 1.7 improvement over previous results. Scale-invariant backgrounds are constrained to ${\mathrm{\Omega }}_{\mathrm{GW}}(25\mathrm{Hz})\le 2.8\times {10}^{-9}$, representing a $2.1\times$ sensitivity gain. We also place new limits on alternative gravity theories predicting nonstandard polarization modes and confirm that terrestrial magnetic noise sources remain below our detection threshold. Combining these spectral limits with population models for Gravitational-Wave Transient Catalog (GWTC)-4, the latest gravitational-wave event catalog, we find our constraints remain above predicted merger backgrounds but are approaching detectability. The joint analysis combining the background limits shown here with GWTC-4 enables improved inference of the binary black hole merger rate evolution across cosmic time. Furthermore, employing GWTC-4 inference results and standard modeling choices, we estimate that the total background arising from compact binary coalescences is ${\mathrm{\Omega }}_{\mathrm{CBC}}(25\mathrm{Hz})={0.9}_{-0.5}^{+1.1}\times {10}^{-9}$ at 90% confidence, where the largest contribution is due to binary black holes only, ${\mathrm{\Omega }}_{\mathrm{BBH}}(25\mathrm{Hz})={0.8}_{-0.5}^{+1.1}\times {10}^{-9}$.

In this work we study the radiative decays of $B\to \rho (\omega )\gamma$ processes in the modified perturbative QCD approach, where the transverse momenta of the quark and gluons involved in the interaction process are kept, and the Sudakov factor is incorporated in the theoretical calculation, which are helpful to suppress the infrared end point contribution. A critical infrared momentum cutoff scale is introduced, which is used to separate the soft and hard contributions in QCD. Then the form factors involved in the radiative decays should be separated as hard and soft form factors. The hard form factors can be calculated with the perturbative QCD approach, while the soft form factors should be viewed as soft input parameters. The soft form factors can be obtained by confronting the theoretical calculation of the branching ratios of the radiative decay of $B$ meson with the experimental data. Summing the soft and hard form factors, we find that the total form factors are in fine agreement with that obtained by nonperturbative theoretical method, such as the light-cone sum rules of QCD. We also study $B\to \rho (\omega ){\gamma }^{\prime }$ decays by using the form factors obtained in the $B\to \rho (\omega )\gamma$ decay processes, where ${\gamma }^{\prime }$ is the dark photon introduced by the extra $U(1)$ symmetry model. The upper limit of the branching ratios of these decays are estimated.

We investigate a mechanism for generating mass terms in the Ishibashi–Kawai–Kitazawa–Tsuchiya (IKKT) and Banks–Fischler–Shenker–Susskind (BFSS) matrix theories through compactification on a torus and the derivation of a zero-mode effective theory, emphasizing the crucial role of fermionic boundary conditions. Extending a recent proposal developed for the IKKT model to the BFSS framework, we explore a broader class of mixed fermionic boundary conditions in both theories. This choice leads to a distinct effective theory with intermediate features, where a mass term is generated together with fermionic zero-modes. In the BFSS case, this setup further allows for the construction of black hole solutions. The resulting geometry takes the form of a fuzzy sphere, with quantum excitations in the fermionic sector accounting for the corresponding black hole entropy.

In this paper, we address a foundational challenge in quantum field theory on curved spacetime by developing a consistent framework in spherically symmetric loop quantum gravity. We introduce a methodology for defining meaningful superpositions of quantum geometry and matter states near the semiclassical apparent horizon. This is achieved by identifying a restricted subspace of the gravitational phase space, which ensures unitary equivalence among Fock representations of a scalar field across different quantum geometries. Within the resulting well-defined state space, we derive weak solutions to the quantum Hamiltonian constraint of general relativity near the semiclassical apparent horizon. Furthermore, we generalize the Hartle-Hawking vacuum state to this quantum geometric framework. The resulting state exhibits the inherent entanglement between geometry and matter, which arises from the quantum Hamiltonian constraint of general relativity. This work establishes a principled framework for studying geometry-matter entanglement and offers new insights into the quantum foundations of the black hole information paradox.

We present a numerical-relativity study of comparable-mass boson star–black hole (BS-BH) head-on collisions, focusing on both initial-data construction and gravitational-wave (GW) phenomenology. We show that plain superposition can strongly perturb the BS core, leading to large constraint violations and unphysical radial oscillations. To remedy this problem, we introduce a one-body conformal-factor correction and find that it substantially suppresses these artifacts. Using the improved initial data, we analyze GW emission from equal- and unequal-mass BS-BH binaries and compare with matched BS-BS and BH-BH baselines. For equal masses, the BS-BH radiated energy increases with BS compactness and approaches the BH-BH limit for highly compact stars. For unequal masses, the $q=2$ BS-BH configuration in our sample radiates slightly more GW energy than its matched BH-BH counterpart.

The inspiral of a compact object into a black hole is a key source of low-frequency gravitational waves for future space-based detectors like LISA. While models of this process have advanced considerably, they typically focus on asymptotically flat spacetimes. In this paper, we investigate how departures from asymptotic flatness, whether driven by cosmic expansion or large-scale galactic environments, alter adiabatic orbital evolution. Using the Schwarzschild–de Sitter (SdS) metric, we parametrize these deviations via an“SdS parameter” ($\lambda$) and analyze its impact on bound orbits. We calculate how $\lambda$ shifts the separatrix between bound and plunging states and modifies the relationship between a binary’s energy, angular momentum, and orbital geometry. By applying a modified quadrupole formula in the weak-field limit, we investigate the effect of $\lambda$ on circularization, plunge times, and orbital trajectories. We show that a positive SdS parameter accelerates eccentricity decay and shortens inspiral timescales. We also generate adiabatic waveforms from inspirals evolving under radiation reaction, exhibiting an increase in amplitude and a cumulative phase advance induced by $\lambda$. While these effects are negligible if $\lambda$ is strictly cosmological, they become observationally relevant if the parameter serves as a proxy for astrophysical environments that induce $\sim r^2$ potential corrections. Our results suggest that such environmental coupling could meaningfully bias event rate estimates and waveform templates for space-based gravitational wave astronomy.

Fast radio bursts (FRBs) are increasingly recognized as powerful cosmological tools for constraining the baryon fraction in extragalactic diffuse ionized gas, presenting a promising approach to address the missing baryon problem. In this paper, we constrain the baryon fraction in extragalactic diffuse ionized gas ($f_{\mathrm{d}}$) utilizing the latest sample of 124 localized FRBs across three different cosmological models. Our analysis models the probability distribution of the extragalactic diffuse ionized gas dispersion measure with a form that accurately reproduces mock observations. For a constant $f_{\mathrm{d}}$ model, we find that more than 90% of baryons reside in the diffuse ionized gas phase. This result is robust against the choice of dark-energy parametrization under the current combination of datasets, although the fitted cosmological parameters shift accordingly. We also find that the inferred $f_{\mathrm{d}}$ is sensitive to the assumed dispersion measure distributions of both the Milky Way halo and the FRB host galaxies. Furthermore, the current data do not show statistically significant evidence for redshift evolution in $f_{\mathrm{d}}$, but the constraints are limited by the redshift distribution of the sample. Our conclusions are insensitive to the adopted baryonic feedback parameters and to the dispersion measure selection effect. These results provide strong evidence that the majority of the missing baryons reside in the diffuse ionized intergalactic medium.

We study the equation of state of neutron-star matter with color-spin molecular dynamics. The calculation includes the internal color and spin degrees of freedom and their time evolution. The matter composition, including strangeness under $\beta$ equilibrium, is determined by energy minimization. We find two main trends. First, within the present color-spin molecular dynamics framework and under the adopted clustering criterion along the stable neutron-star branch, isolated quarklike configurations do not appear; instead, color-magnetic interactions favor the self-consistent formation of multiquark clusters. Within the same criterion, the cluster-size distribution is concentrated at quark numbers that are multiples of three, corresponding to integer baryon numbers. Second, relative to the conventional no-$K^{*}$ baseline, the interaction between strange and light quarks has a strong impact on neutron-star radii. This suggests that future radius measurements, together with phenomenological information on the strangeness-onset density, may help constrain flavor-sector interactions involving strangeness.

In this paper, based on the noncommutative geometry-inspired Schwarzschild black hole, we employ a third-order WKB approximation approach to systematically calculate the quasinormal mode frequencies (QNFs), greybody factors (GFs), and absorption cross section (ACS) under massive scalar field perturbations. The results show that the QNFs satisfy $\mathrm{Im}(\omega )<0$, confirming the stability of the black hole under perturbations. Furthermore, increasing the noncommutative parameter $\theta$ reduces the absolute values of both the real and imaginary parts of the frequency, while increasing the mass $\mu$ increases the real part and reduces the imaginary part. The GFs and ACS increase with increasing $\theta$ and decrease with increasing $\mu$, indicating opposite modulation effects of these two types of parameters. It is worth emphasizing that the QNFs of the extreme black hole approach the corresponding values of the classical Schwarzschild black hole at angular quantum number $\ell =1$ and large $\mu$, suggesting that the effects of mass and noncommutative geometry quantum corrections cancel each other out to some extent. It is hoped that these results provide a viable theoretical basis for both the theoretical and experimental aspects of the perturbative dynamics of black holes.

High-energy neutrinos provide a potentially powerful and distinctive probe for dark matter (DM)–neutrino interactions, particularly in environments with enhanced DM densities, such as the DM spikes predicted to form around supermassive black holes at the center of active galactic nuclei (AGN). Recent results by the IceCube Neutrino Observatory, which reported four significant AGNs, namely TXS $0506+056$, NGC 1068, PKS $1424+240$, and NGC 4151 as candidate neutrino sources, provide a valuable opportunity to search for signatures of these interactions. In this study, we use IceCube data to derive the most stringent constraints to date on both the energy-dependent and energy-independent DM-neutrino scattering cross sections. We perform a statistical analysis using data from individual sources as well as a combined (stacked) analysis of all four sources. Our strongest limits arise from the stacking analysis, yielding an upper bound of ${\sigma }_0\lesssim 8\times {10}^{-39}{\mathrm{cm}}^2$ for an energy-independent cross section and ${\sigma }_0\lesssim {10}^{-39}{\mathrm{cm}}^2$ for a linearly energy-dependent cross section, both at 90% confidence level, particularly in scenarios involving the adiabatic growth of black holes.

While the potential of the Jiangmen Underground Neutrino Observatory (JUNO) to measure solar neutrinos is known, realizing this potential requires new techniques to reduce detector backgrounds. One of the most serious backgrounds is due to the beta decays of unstable nuclei produced through muon breakup (spallation) of nuclei. This background is much more significant in JUNO compared to Super-Kamiokande due to JUNO’s shallower depth and its lack of directional information. We present the first detailed theoretical calculations of spallation backgrounds in JUNO, showing the underlying physical processes and new ways to cut backgrounds while preserving signals. A key point is showing the importance of neutron tagging to identify hadronic showers, which are rare but produce almost all of the dangerous isotopes. With our new techniques, JUNO will be able to reduce dead time (signal loss) by a factor of about 4.5 and to reduce the running time needed to meet sensitivity goals by a factor of 2. This will give JUNO greatly improved sensitivity to ${}^8\mathrm{B}$ and $hep$ solar neutrinos, as we will explore in a separate paper.

We perform a complete one-loop renormalization analysis of $CPT$-odd Lorentz-violating scalar quantum chromodynamics with adjoint scalar matter. Working to first order in the preferred background vector and treating the corresponding operators as perturbative insertions, we compute the ultraviolet-divergent parts of the relevant two-, three-, and four-point Green’s functions for the gauge, scalar, and ghost fields. We show that the gauge sector develops the expected Carroll-Field-Jackiw-type correction, which generically turns out to be divergent in our theory, although the divergence vanishes in a certain gauge, while the scalar sector displays the corresponding $CPT$-odd single-derivative term proportional to the background vector. We further demonstrate that several of the Lorentz-violating corrections the three- and four-point function are ultraviolet finite. All one-loop divergences may be absorbed into counterterms already allowed by the classical Lagrangian, providing an explicit proof of the multiplicative renormalizability of the theory at this order. We also obtain the associated renormalization constants and one-loop $\beta$ functions for the gauge coupling, the Lorentz violation parameters, and the scalar self-interaction.

In gauge theory on 5D orbifolds the magnitude of chiral anomalies of 4D gauge fields changes with the value of the Aharonov-Bohm (AB) phase ${\theta }_H$ in the fifth dimension. Anomaly flows with the AB phase. In particular in the Randall-Sundrum (RS) warped space gauge couplings of 4D fermions depend on bulk mass parameters of 5D fermion multiplets. We show that in the GUT-inspired $SO(5)\times U(1)\times SU(3)$ gauge-Higgs unification model in the RS warped space the total anomalies including contributions of all Kaluza-Klein excited modes of fermions become universal, being independent of the values of the bulk mass parameters of fermions and expressed in terms of the values of $W$ and $Z$ wave functions at the ultraviolet and infrared branes in the RS space. It is shown that cancellation of gauge anomalies is achieved in each generation even for ${\theta }_H\ne 0$.

By studying a simple model of relativistic particles propagating through a background medium with an energy-dependent relaxation time that is unbounded from above, we investigate how long-term memory obstructs the emergence of local hydrodynamics in systems with a gapless nonhydrodynamic sector. In the relaxation-time approximation matching frame, we show that the full gradient expansion is generically divergent in most flows, even for Fourier modes, and that any resummation necessarily retains an infinite set of slow nonhydrodynamic degrees of freedom. The divergence of the gradient expansion therefore reflects a more fundamental breakdown of hydrodynamic locality caused by persistent nonhydrodynamic memory. We finally show that sufficiently singular relaxation spectra can invalidate ordinary diffusion itself. In these regimes, the diffusivity diverges, and the late-time dynamics become superdiffusive, governed by intrinsically nonlocal constitutive relations.

We present a charged-current quasielastic neutrino-nucleus scattering model based on an unfactorized representation of the spectral function, employing relativistic momentum distributions for bound nucleons and the relativistic distorted-wave impulse approximation with an energy-dependent relativistic potential to describe the scattered nucleon. The model incorporates two-body meson-exchange currents contributing to one-particle-one-hole final states and tests several axial form factor parametrizations, including recent LQCD and MINERvA fits. It is implemented in the NEUT event generator and benchmarked against T2K and MINERvA ${\nu }_{\mu }\text{−}{}^{12}\mathrm{C}$ $\mathrm{CC}0\pi$ measurements. We find that two-body meson-exchange currents lead to a sizeable increase of the total cross section, arising from an enhancement of the transverse response, which is the dominant component in charged-current neutrino scattering. On the other hand, recent fits of the axial form factor predict larger values than the standard dipole form, yielding a systematic enhancement of the cross section. The $\mathrm{LQCD}+\mathrm{MINERvA}$ parametrization tends to overestimate the data, while the MINERvA-only fit provides a more moderate increase. Overall, no single configuration consistently provides the best agreement with the different datasets.

The flux of Hidden Sector particles from the Galactic halo reaching an underground detector can be significantly attenuated by interactions within the Earth for sufficiently large scattering cross- sections. This attenuation gives rise to a characteristic daily modulation in the detection rate, due to Earth’s rotation. We present results from a search for such a modulation using a 1.257 kg-day dataset collected with the DAMIC-M Low Background Chamber. A model-independent analysis reveals no significant modulation in the $1e^{-}$ event rate over periods from 1 to 48 h, highlighting the excellent temporal stability of the detector. In a complementary model-dependent analysis, we target the expected daily modulation signature of Hidden Sector particles, with masses in the range $[0.53,2]\mathrm{MeV}/{\mathrm{c}}^2$, interacting with electrons via a dark photon mediator. By leveraging the expected temporal evolution of the signal, we set improved constraints on Dark Matter masses below $1.2\mathrm{MeV}/{\mathrm{c}}^2$, surpassing our previous limits.