Motivated by the out-of-equilibrium dynamics during an early-Universe first-order phase transition, we perform real-time simulations of fermion-bubble scattering in $1+1$ dimensions. This nonequilibrium process can generate a charge-conjugation $C$ asymmetry outside the bubble wall, induced by the complex fermion mass profile. The resulting $C$ asymmetry is the $1+1$-dimensional analog of the $CP$ asymmetry in $3+1$ dimensions, a key ingredient in baryon asymmetry generation at the electroweak scale. Using tensor network methods, we track the real-time evolution of the $C$ asymmetry in the charge density as the fermion interacts with the bubble wall, a regime inaccessible to analytic calculations. We further introduce two observables to quantify the asymmetry in the asymptotic region where reflected particles are well separated from the scattering point: one based on the net charge outside the bubble wall, and the other on the spatial displacement between the reflected particle and antiparticle wave packets. Our study represents a first step toward nonperturbative, real-time computations of $CP$ asymmetry in $3+1$ dimensions for electroweak baryogenesis.

We establish a factorization relation between baryon quasidistribution amplitudes (quasi-DAs) defined with gradient flow and their counterparts renormalized in the $\overline{\mathrm{MS}}$ scheme. Working beyond the small flow-time limit, we perform a complete one-loop calculation that yields the full matching kernel and the associated Wilson-line linear divergence for flowed quasi-DAs. Building on this relation, we formulate a hybrid renormalization scheme that combines ratio scheme with gradient-flow matching, thereby replacing fit-dependent self-renormalization and improving theoretical control over scheme conversion. The framework enables a systematic connection between lattice QCD matrix elements and continuum baryon quasi-DAs, with reduced renormalization uncertainties and clear guidance for practical lattice analyses.

We investigate the boundary reduction of 3D Einstein gravity and Jackiw-Teitelboim gravity into their respective edge mode theories—namely, the Liouville and Alekseev-Shatashvili, and Schwarzian models. By examining the roles of boundary conditions, canonical transformations, and differing formulations—metric versus Chern-Simons—we clarify how physical degrees of freedom become localized at the boundary and resolve several longstanding ambiguities in the reduction procedure.

Pulsar timing arrays have reported a compelling evidence of a nanohertz stochastic gravitational wave background. However, the origin of the signal remains undetermined, largely because its spectrum is bluer for an astrophysical source and can be explained by cosmological models. In this letter, we revisit the frequency- and Fourier-domain analysis of the signal by deriving theoretically accurate expressions for the Fourier bin variances and correlation of pulsar timing residuals, and demonstrate their outstanding agreement with point source astrophysical simulations. In contrast, we show that a common power law (or a diagonal covariance approximation) traditionally used to interpret a stochastic gravitational wave background signal is generally faced with systematic errors, one of which is the illusion of a bluer signal. This hints at a conservative solution, supportive of an astrophysical source, to the observed correlated common spectrum process in pulsar timing arrays.

We derive a general relation between the background effective actions, which directly proves that the two formulations of the Einstein-Hilbert theory with background fields are equivalent at the quantum level. This basic result has been substantiated in a general background gauge by explicit calculations at one-loop order of the corresponding counterterm Lagrangians.

It is well established that black holes in four-dimensional, vacuum, general relativity exhibit vanishing static tidal Love numbers, indicating no multipolar response to the external tidal fields in the static limit. This intriguing feature does not extend to higher-dimensional spacetimes within general relativity, where static black holes can possess nonzero static tidal Love numbers (TLNs). In this work, we have examined the tidal deformation of black holes in Lovelock gravity. We find that, in certain cases within pure Lovelock gravity, the static TLN vanishes, extending the four-dimensional result to specific higher-dimensional settings. On the other hand, black holes in Einstein-Gauss-Bonnet gravity consistently exhibit nonzero static TLNs, with their magnitude depending on the Gauss-Bonnet coupling constant. Exceptions occur only in certain special cases associated with axial perturbations. These results highlight the sensitivity of the multipolar response of a black hole under tidal field, to the underlying theory of gravity and the spacetime dimensions.

Cross-correlation analysis of detector pairs is a standard method for probing the stochastic gravitational-wave background (SGWB). The correlation signal is determined by the SGWB intensity and the geometric sensitivity of the detector pair, which can be quantified by the overlap reduction function (ORF). In our previous work [Phys. Rev. D 111, 084065 (2025)], we developed a formula to calculate the ORF of the SGWB with tensor polarization for pulsar timing arrays (PTAs) and laser interferometer detectors without approximation. In this work, we generalize the method to calculate the ORF for vector and scalar polarizations that may be present in alternative theories of gravity. This formula is valid for any experiment measuring variations in light travel time between two points due to gravitational waves. Using this formula, we derive expressions for the ORFs of PTAs, ground-based interferometers, and space-based interferometers for all polarizations. Furthermore, this universal formula provides enhanced accuracy for ORF calculations in high-frequency regimes of third-generation ground-based interferometers and space-based interferometers. An important practical implication is its ability to break the degeneracy between scalar-breathing and scalar-longitudinal polarizations that arises in the small-antenna approximation, thereby providing a foundation for distinguishing them in data analysis.

Bañados, Teitelboim, and Zanelli (BTZ) spacetime is a long-known locally anti–de Sitter (AdS) solution to the Einstein equations in 1 timelike and 2 spacelike dimensions. Its static variant is interpreted as a black hole whose mass is related to the period of the angular coordinate. This solution can be parametrically continued into one without horizons but with a conical deficit in the center. Such a solution is interpreted as a spacetime with a massive particle. It has been shown that this particle can be in static equilibrium with a cosmic string passing through the spacetime to infinity. In this work, we explore the interaction of point particles with strings, such as a bound system of two particles connected by a string of finite length. We identify additive local mass in the static spacetimes and apply it to the case of particles and strings. Finally, using the cut and glue method, we construct the system of two particles oscillating on the string, which goes out of the scope of static systems.

In this work, we introduce a family of rotating black bounces with an anisotropic fluid obtained by using a modified Newman-Janis algorithm. We analyze the main features of these spacetimes and obtain the geodesics for photons, which admit the separation of the Hamilton-Jacobi equation. We then determine the shape of the shadow in terms of the parameters of the model. We present some relevant examples that exhibit some traits that distinguish these spacetimes from other related ones appearing in the literature.

The numerical waveforms for the extreme mass-ratio inspirals (EMRIs) require a huge amount of homogeneous solutions of the Teukolsky equation in the frequency domain. The calculation accuracy and efficiency of the homogeneous solutions are the key performance bottleneck in waveform generation. In this paper, we propose a new numerical method based on the analytical series expansion, which is most efficient for computing the homogeneous solutions with very high accuracy and a wider frequency range compared with the existing methods. Our new method is definitely useful for constructing the waveform templates of EMRIs.

We classify $f(R)$ theories using a mathematical analogy between slow-roll inflation and the renormalization-group flow. We derive the power spectra and spectral indices class by class and compare them with the latest data. The framework used for the classification allows us to determine the general structure of the $f(R)$ functions that belong to each class. Our main result is that only two classes survive. Moreover, we show that the Starobinsky model is the only polynomial $f(R)$ that can realize slow-roll inflation. In fact, all other polynomials belong to a special class that can only realize constant-roll inflation, at least far enough in the past. We point out some of the issues involved in considering a smooth transition between constant-roll and slow-roll inflation in this class of models. Finally, we derive the map that transforms the results from the Jordan frame to the Einstein frame.

We critically examine recent claims challenging the viability of the G-step model (GSM) as a solution to the Hubble tension. The GSM proposes a $\sim 4\%$ increase in the effective gravitational constant $G_{\mathrm{eff}}$ beyond $z\approx 0.01$ to reconcile local and early-universe measurements of the Hubble constant. Through detailed quantitative analysis, we demonstrate that many proposed constraints on the model require careful reconsideration. Key findings include: (1) Modern stellar modeling indicates a weaker $L\propto G^4$ scaling rather than the traditional $G^7$, significantly reducing tension with stellar evolution constraints; (2) The fluidlike behavior of Earth 150 Myr ago preserves the day/year ratio across any $G$ transition; (3) Paleoclimate data showing $\sim 20°\mathrm{C}$ cooling over relevant timescales appears consistent with, rather than challenging, the GSM; (4) Distance indicator comparisons allow for $\mathrm{\Delta }G/G$ variations up to $\sim 20\%$ at $2\sigma$ when systematic uncertainties are properly included; (5) The discrete nature of the proposed $G$ transition preserves relative stellar population ages used in cosmic chronometry. When accounting for proper uncertainty levels in both observations and theoretical modeling, we find the GSM remains a viable candidate for resolving the Hubble tension. We identify specific observational tests with next-generation facilities that could definitively confirm or rule out the model.

While the equation of state (EOS) $P(ϵ)$ of neutron star (NS) matter has been extensively studied, the EOS-parameter $\varphi =P/ϵ$ or equivalently the dimensionless trace anomaly $\mathrm{\Delta }=1/3-\varphi$, which quantifies the balance between pressure $P$ and energy density $ϵ$, remains far less explored, especially in NS cores. Its bounds and density profile carry crucial information about the nature of superdense matter. Physically, the EOS-parameter $\varphi$ represents the mean stiffness of matter accumulated from the stellar surface up to a given density. Based on the intrinsic structure of the Tolman-Oppenheimer-Volkoff equations, we show that $\varphi$ decreases monotonically outward from the NS center, independent of any specific input NS EOS model. Furthermore, observational evidence of a peak in the SSS density profile near the center effectively rules out a valley and a subsequent peak in the radial profile of $\varphi$ at similar densities, reinforcing its monotonic decrease. These model-independent relations impose strong constraints on the near-center behavior of the EOS-parameter $\varphi$, particularly demonstrating that the mean stiffness (or equivalently $\mathrm{\Delta }$) reaches a local maximum (minimum) at the center.

We present a comprehensive investigation into the phenomenological consequences of axionlike particle (ALP) mediated dark matter (DM) on the structure of neutron stars (NSs). Our analysis is grounded in a well-established relativistic mean-field framework, featuring nonlinear mesonic self-interactions constrained by nuclear physics data and modern astrophysical observations. We systematically explore the DM parameter space, spanning DM particle masses $m_{\chi }\in [0,1000]\mathrm{GeV}$ and DM fermi momenta $q_f\in [0,0.06]\mathrm{GeV}$, by generating a vast ensemble of over 30,000 equations of state (EoSs). This analysis is carried out using two representative hadronic EoSs, a stiff one (EoS1) and a soft one (EoS18), with the explicit inclusion of the crustal EoS to properly account for the low-density regime of NSs. Employing a multitiered statistical filtering scheme, combining voting, likelihood, and kernel density estimation scores, we apply stringent constraints from a suite of multimessenger observations, including radio and x-ray pulsars, GW170817, and low-mass compact object HESS J1731-347, revealing that models satisfying the PSR J0614-3329 radius bound inherently comply with the HESS constraints, positioning ALP-mediated DM as a viable candidate for explaining low-mass compact objects while still supporting $2M_{\odot }$ NSs. For the stiff EoS, we obtain a lower bound of $m_{\chi }\gtrsim 43\mathrm{GeV}$, with score-weighted posteriors favoring $q_f=0.034_{-0.012}^{+0.020}$ and a broad allowed DM mass range $m\chi \in [101,949]\mathrm{GeV}$ (median $\sim 466\mathrm{GeV}$). In contrast, the soft EoS yields no strict lower bound on $m_{\chi }$, although scenarios with simultaneously large $m_{\chi }$ and $q_f$ are strongly disfavored. We developed a high-precision supervised interpolation model using AutoGluon to infer DM parameters from reconstructed NS mass-radius curves, achieving $R^2>0.998$. Feature-importance analysis indicates that the DM mass $m_{\chi }$ is mainly constrained by global shape indicators such as the radius ratio $R_{1.6}/R_{1.4}$, whereas the Fermi momentum $q_f$ is primarily determined by the tidal deformability ${\mathrm{\Lambda }}_{1.4}$.

Pulsar timing arrays (PTAs) are anticipated to detect continuous gravitational waves (GWs) from individual supermassive black hole binaries (SMBHBs) in the near future. To identify the host galaxy of a GW source, PTAs require significantly improved angular resolution beyond the typical range of 100–1000 square degrees achieved by recent continuous GW searches. In this study, we investigate how precise pulsar distance measurements can enhance the localization of a single GW source. Accurate distance information, comparable to or better than the GW wavelength (typically 1 pc) can refine GW source localization. In the near future, with the advent of Square Kilometre Array (SKA), such high-precision distance measurements will be feasible for a few nearby pulsars. We focus on the relatively nearby pulsars J0437-4715 (156 pc) and $\mathrm{J}0030+0451$ (331 pc), incorporating their actual distance uncertainties based on current very long baseline interferometry measurements and the anticipated precision of the SKA-era. By simulating 87 pulsars with the GW signal and Gaussian white noise in the timing residuals, we assess the impact of the pulsar distance information on GW source localization. Our results show that without precise distance information, localization remains insufficient to identify host galaxies under 10 ns noise. However, incorporating SKA-era distance precision for nearby pulsars J0437-4715 and $\mathrm{J}0030+0451$ can reduce localization uncertainties to the required level of ${10}^{-3}{\mathrm{deg}}^2$ under 10 ns noise. Localization accuracy strongly depends on the geometric configuration of pulsars with well-measured distances and improves notably near and between such pulsars. The improvement of the localization will greatly aid in identifying the host galaxy of a GW source and constructing an SMBHB catalog. It will further enable follow-up electromagnetic observations to investigate the SMBHB in greater detail.

Is field space infinite? If not, it either loops back on itself or ends altogether. Periodic boundary conditions are of course familiar, but field space endpoints—which appear in real-world systems—are far less explored. In this paper we argue that boundaries in field space are generic, radiatively stable structures that allow for new physics at very low scales not ruled out by experiment. Such boundaries are delocalized in field space from the vacuum, so they can only be accessed by coherent fields or high multiplicity processes, both of which are weakly constrained observationally. Low multiplicity interactions do not detect the boundary and instead perceive a “mirage cutoff” that is parametrically higher than the true cutoff of the theory. Hence, field space boundaries are deformations of the standard model that are Lorentz invariant, local, unitary at low energies, and experimentally unconstrained. We comment on the possibility of field space boundaries on the long-range force carriers and the Higgs, as well as possible implications for the hierarchy problem.

We propose a phase-coherent, narrowband magnetometer for searching couplings between axions and axionlike particles and electron spins, using gate-defined silicon quantum dot spin qubits. With repeated Ramsey echo sequences and dispersive readout, the qubit precession response can be tracked with sub-Hz spectral resolution. The accessible axion mass window is determined using a series of filtering protocols with consideration of sensing noise (including readout errors and $1/f$ noise). We demonstrate clear indication of sidereal modulation of the signal due to Earth’s rotation, while Earth’s orbital motion induced annual amplitude envelope that generates sidebands at fixed frequency spacing $\pm {\mathrm{\Omega }}_{\oplus }$ around the sidereal component, for axion mass between $1-10\mathrm{\mu }\mathrm{eV}$, our proposed method covers $g_{ae}$ from ${10}^{-14}$ to ${10}^{-10}$. Incorporating this daily and annual modulation pattern in a likelihood analysis enhances the rejection of stationary or instrumental noise. Our analysis indicates that spin-qubit magnetometry can achieve sensitivities approaching those suggested by astrophysical considerations, thus providing a complementary, laboratory-based probe of axion-electron interactions. Although we focus on silicon spin qubit architectures, the approach is broadly applicable to spin-based quantum sensors.

The inverse seesaw (ISS) model provides an attractive framework that can naturally explain the smallness of neutrino masses while accommodating some sterile neutrinos potentially accessible at present or future experiments. However, in generic ISS models with hierarchical pseudo-Dirac (PD) sterile neutrino pairs, the generation of the observed baryon asymmetry of the Universe via the leptogenesis mechanism is extremely challenging. In this paper, we investigate rescuing leptogenesis in the ISS model with the help of non-Abelian flavor symmetries, which have the potential to explain the observed peculiar neutrino mixing pattern: we first implement non-Abelian flavor symmetries to naturally enforce mass degeneracies among different pseudo-Dirac sterile neutrino pairs and then break them in a proper way so that resonant leptogenesis among different PD sterile neutrino pairs can arise, thus enhancing the generated baryon asymmetry. To be specific, we have considered the following two well-motivated approaches for generating the tiny mass splittings among different PD sterile neutrino pairs: one approach makes use of the renormalization-group corrections to the sterile neutrino masses, while the other approach invokes nontrivial flavor structure of the ${\mu }_{\mathrm{s}}$ matrix. For these two scenarios, we aim to explore the viability of leptogenesis and to identify the conditions under which the observed baryon asymmetry can be successfully reproduced.

The exploration of exotic mesons, which transcend the conventional quark-antiquark framework, is pivotal for advancing our understanding of QCD and the strong interaction. Among these, states possessing the quantum numbers $J^{PC}=1^{-+}$, such as ${\pi }_1(1600)$, ${\pi }_1(2015)$, and the recently discovered ${\eta }_1(1855)$, have attracted significant attention due to their potential hybrid nature, which involves gluonic excitations. However, the physical interpretation of these states remains contentious, primarily due to inconsistencies between theoretical predictions and experimental observations regarding their decay widths and mass spectra. To address these challenges, we employ a potential model inspired by SU(3) lattice gauge theory to calculate the masses of light-flavor $1^{-+}$ hybrid states and utilize the constituent gluon model to analyze their strong decay properties. Our mass calculations suggest that while the ${\pi }_1(1600)$ and ${\eta }_1(1855)$ masses are in close agreement with the predicted hybrid states, the corresponding decay widths for ${\pi }_1(1600)$ and ${\pi }_1(2015)$ do not support their classification as hybrids, implying alternative interpretations, such as tetraquark or molecular configurations. Conversely, the ${\eta }_1(1855)$ is consistent with a mixed hybrid state composed of $(u\overline{u}+d\overline{d})g/\sqrt{2}$ and $s\overline{s}g$ components, with mixing angles ranging from 17.7° to 84.2°. Additionally, we predict the masses and decay widths of yet-unobserved isoscalar and excited hybrid states, providing valuable targets for future experimental searches. This study not only clarifies the hybrid nature of certain exotic mesons but also contributes to the systematic classification of hybrid states within the meson nonet, thereby enhancing our comprehension of exotic hadronic states.

The determination of the shear viscosity is a central topic in various areas of modern physics. In particular, it is often necessary to evaluate the shear viscosity $\eta$ of fluids made up of more than one species, all interacting with different cross sections. Since it may be difficult to extract information on the interaction among different species, various combinations of the viscosities of the individual components are often used. We work in the Chapman-Enskog framework and investigate binary mixtures, by comparing such single component combinations with a full 2-component formalism: we find that, in most cases, the full viscosity is well approximated by a weighted linear average of the single component viscosities, although this result is far from being general. Moreover, we validate our 2-component Chapman-Enskog results for $\eta$ by comparing them with an independent numerical simulation of the Boltzmann equation, which estimates the shear viscosity via a Green-Kubo formula, in the case of a quasiparticle system that reproduces lattice QCD thermodynamics. We see that the temperature dependence of $\eta /s$ of such a system of quarks and gluons is not well described by combinations of the individual components, highlighting the importance of interspecies scattering.