Eccentric white dwarf-massive black hole binaries can potentially source some extreme x-ray transients, including tidal disruption events and the recently observed quasiperiodic x-ray eruptions at the galactic nuclei. Meanwhile, they are one of the target gravitational wave sources with extreme mass ratios for future millihertz gravitational wave missions. In this work, we focus on the tidal evolution and orbital dynamics of such binaries under the influence of the tidal backreaction and the dissipative effect from gravitational wave emission. We find that the latter can cause the dynamical tide to evolve chaotically after more than one orbital harmonics encounter the mode resonance through orbital decay. Different from the tidal-driven chaos, which only occurs for pericenter distances within around two times the tidal radius ($R_t$), this gravitational wave-driven chaos can happen at much larger pericenter distances. The growth scales similarly to a diffusive process, in which the tidal energy grows linearly with time on average over a long duration. If the tidal energy eventually approaches the stellar binding energy, achievable when the pericenter distance is less than $4R_t$, it can cause mass ejection as the wave breaks due to nonlinear effects. We show that this can potentially lead to the repeating partial tidal disruptions observed at galactic centers. That means these disruptions can occur at a much larger pericenter distance than previous analytical estimates. Furthermore, if the system can evolve to a close pericenter distance of about 2.7$R_t$, the white dwarf can further lose mass via tidal stripping at each pericenter passage. This provides a mechanism for producing the quasiperiodic eruptions. However, it requires at least a certain amount of angular momentum to escape the binary during the mass transfer process to match the observations, which we do not have a justification based on first-principle calculations.

Perturbative quantum chromodynamics (pQCD), while valid only at densities exceeding those found in the cores of neutron stars, could provide constraints on the dense-matter equation of state (EOS). In this work, we examine the impact of pQCD information on the inference of the EOS using a nonparametric framework based on Gaussian processes (GPs). We examine the application of pQCD constraints through a “pQCD likelihood,” and verify the findings of previous works; namely, a softening of the EOS at the central densities of the most massive neutron stars and a reduction in the maximum neutron-star mass. Although the pQCD likelihood can be easily integrated into existing EOS inference frameworks, this approach requires an arbitrary selection of the density at which the constraints are applied. The EOS behavior is also treated differently on either side of the chosen density. To mitigate these issues, we extend the EOS model to higher densities, thereby constructing a “unified” description of the EOS from the neutron-star crust to densities relevant for pQCD. In this approach the pQCD constraints effectively become part of the prior. Since the EOS is unconstrained by any calculation or data between the densities applicable to neutron stars and pQCD, we argue for maximum modeling flexibility in that regime. We compare the unified EOS with the traditional pQCD likelihood, and although we confirm the EOS softening, we do not see a reduction in the maximum neutron-star mass or any impact on macroscopic observables. Though residual model dependence cannot be ruled out, we find that pQCD suggests the speed of sound in the densest neutron-star cores has already started decreasing toward the asymptotic limit; we find that the speed of sound squared at the center of the most massive neutron star has an upper bound of $\sim 0.5$ at the 90% level.

Over the past 16 years, the Fermi Large Area Telescope (LAT) has significantly advanced our view of the GeV gamma-ray sky, yet several key questions remain—such as the composition of the isotropic gamma-ray background, the origin of the Fermi Bubbles, or the potential presence of signatures from exotic physics like dark matter. Addressing these challenges requires sophisticated astrophysical modeling and robust statistical methods capable of handling high-dimensional parameter spaces. In this work, we analyze 14 years of high-latitude ($|b|\ge 30°$) Fermi-LAT data in the range from 1 to 10 GeV using simulation-based inference (SBI) via neural ratio estimation. This approach allows us to detect individual gamma-ray sources and derive a list of significant gamma-ray emitters containing more than 98% of all sources listed in the Fermi-LAT Fourth Source Catalog (4FGL) with a flux $S>3\times {10}^{-10}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ (about a factor of 3 larger than the flux above which 4FGL is nearly complete), without any non-4FGL source detected in that flux range. Additionally, we reconstruct the source-count distribution in both parametric and nonparametric forms, achieving large agreement with previous literature results as well as those sources detected by our SBI pipeline. We also quantitatively validate our gamma-ray emission simulator via an anomaly detection technique, demonstrating that the synthetic data closely reproduce the complexity of the real observations.

The gravitational wave signal of binary compact objects has two main contributions at frequencies below the characteristic merger frequency; the gravitational wave signal associated with the early inspiral stage of the binary and the nonlinear gravitational wave memory. We compare the sensitivity of upcoming gravitational wave detectors to these two contributions, with a particular interest in events with a merger phase at frequencies higher than the detector’s peak sensitivity. We demonstrate that for light primordial black holes, current and upcoming detectors are more sensitive to the inspiral signal. Our analysis incorporates the evolution history of primordial black hole binaries, key to accurately estimating the relevant event rates. We also discuss the waveform templates of the memory signal at ground- and space-based interferometers, and the implications for a matched filtering search. This allows us to compare the sensitivity of high-frequency gravitational wave detectors, sensitive to the merger phase, with the sensitivity of existing interferometers.

Core-collapse supernovae are among the most energetic astrophysical events in the Universe. Despite huge efforts in understanding the main ingredients triggering such explosions, we still lack compelling evidence for the precise mechanism driving these phenomena. They are expected to produce gravitational waves due to asymmetric mass motions in the collapsing core, and meanwhile emit neutrinos as a result of the interactions in their high-density environment. The combination of these two cosmic messengers can provide a unique probe to study the inner engine of these processes and unveil the explosion mechanism. Among the possible detectable signature, standing accretion shock instabilities (SASIs) are particularly relevant in this context, as they establish a direct connection between gravitational wave emission and the outgoing neutrino flux. In this work, Hilbert-Huang transform is applied to a selected sample of 3D numerical simulations, with the aim of identifying the SASI contribution and extracting its instantaneous frequency. The performance of the method is evaluated in the context of Einstein Telescope.

Light bosonic dark matter fields that can be treated like a classical wave have nonlinear field values close to massive bodies. Here we make the important observation that the quadratic interactions of axion dark matter lead to nonperturbative axion field values for values of the decay constant of $f\lesssim {10}^{13}\mathrm{GeV}$ and masses $m_a\lesssim 7\times {10}^8/f{\mathrm{eV}}^2$ and generalize this result for axionlike particles. We identify experimental observables impacted by this effect.

We characterize the Small Magellanic Cloud pulsar SXP 46.6 using NuSTAR observations conducted in 2017. The spin period ($P$) of this neutron star decreased from its discovered value of 46.6 s to a value of 45.984(1) s, indicating a spin-up at the rate of $\dot{P}=-1.13\times {10}^{-9}\mathrm{s}{\mathrm{s}}^{-1}$. This spin-up rate is used to calculate a high pulsar magnetic field value of $2.25\times {10}^{13}\mathrm{G}$. This process also gives a low magnetic field value, which we rule out here by constraining the inner accretion disk radius to be less than the radius of the innermost stable circular orbit. The pulse profile, analyzed in soft, hard, and broad x-ray bands, shows a double-peaked structure, consistent with pencil beam emission from two antipodal hot spots on the neutron star surface. We also perform spin phase-resolved spectroscopy for the first time, revealing spectral variations across different phases of the pulsar’s rotation. These results offer new insights into the long-term spin evolution and emission properties of SXP 46.6.

Nonminimal couplings between the electromagnetic field strength and the spacetime curvature are part of the effective field theory of gravity and matter. They alter the local propagation of light in a significant way if the ratio of spacetime curvature to the nonminimal coupling is of order one. Spacetime curvature can become appreciable around black holes, and yet the effect of nonminimal couplings on electromagnetic observations of black holes remains underexplored. A particular feature of the nonminimal coupling between the electromagnetic field-strength and the Riemann tensor is that it generates two distinct photon rings for different polarizations. Working within the paradigm of lensing bands and focusing on the $n=1$ lensing band, we illustrate by which diagnostics a modified light propagation may be distinguished from a modified spacetime geometry and how constraints on the value of the nonminimal coupling can be obtained.

Correlated noise sources, particularly magnetic noise, form a risk to future gravitational-wave searches aimed at detecting the gravitational-wave background. To investigate potential noise contamination, we project noise levels based on accurate measurements of how strongly the noise couples to the detector. To make these estimates, we inject, for the first time, broadband, coherent magnetic noise between two gravitational-wave detectors, LIGO Hanford and LIGO Livingston, separated by several thousands of kilometers. We describe the noise injection and its impact on the analysis pipelines, then investigate the accuracy of noise projection techniques used over the past decade. Finally, we present a proof-of-concept demonstration of noise subtraction using Wiener filtering, while also highlighting potential risks associated with this method. This unique dataset with correlated noise caused by magnetic field fluctuations in two gravitational-wave detectors, as well as in an array of witness sensors, provides an excellent testing ground for additional future studies. Ultimately, this study demonstrates that Wiener filtering is effective and can be applied in the eventual detection of the gravitational-wave background by the LIGO-Virgo-KAGRA Collaboration.

Complex-valued Feynman integrals in the imaginary time formalism and zero-temperature limit suffer from particular types of infrared divergences that cannot be regulated by integration dimension alone. Related problems leading to integration-order-dependent results are even further pronounced in the presence of additional scales such as external momenta. This plays a noticeable role in systems featuring fermionic degrees of freedom such as cold quantum chromodynamics, where loop integrals are complexified by chemical potential(s). Working in the limit of vanishing temperature, we utilize novel complex-valued extensions to bubble Feynman integrals and study momentum expansions of fermionic loop integrals. The expansions are then used to illustrate the mechanisms of manifested discrepancies between orders of integration, associated with the residue theorem. Finally, we address the issues by introducing a representation avoiding the observed ambiguity and briefly overview classes of integrals insensitive to problems from external momenta.

An exploratory nonperturbative calculation of the quark propagator in light-cone gauge is motivated by distribution amplitudes whose definition implies a Wilson line. The latter serves to preserve the gauge invariance of the hadronic amplitudes and becomes trivial in light-cone gauge. To that end, we explore the corresponding Dyson-Schwinger equation in its leading truncation and with a dressed vertex derived from a Ward identity in light-cone gauge. The quark’s mass and wave renormalization functions are found to depend on the orientation of the quark momentum relative to the lightlike four-vector below 1 GeV, which expresses the light-cone gauge dependence of the propagator, while a third, complex-valued amplitude exhibits little dependence on that orientation and vanishes in the quark’s rest frame.

In this work, we study the propagation of electromagnetic waves in a magnetized chiral plasma that pervades the interstellar space. The Maxwell equations, supplemented by bi-isotropic-like constitutive relations, are rewritten to describe a cold, uniform, and collisionless plasma model that gives rise to new collective electromagnetic modes characterized by distinct pairs of refractive indices associated with right- and left-handed circularly polarized waves. We analyze the optical behavior through the rotatory power (RP) and the dichroism coefficient, reporting that the finite chiral parameter induces double RP sign reversal, an exotic optical signature that takes place in chiral dielectrics and rotating plasmas. In the low-frequency regime, a modified propagating helicon with right-handed circular polarization is obtained. Next, supposing that the interstellar medium behaves as a chiral bi-isotropic-like cold plasma, we employ astrophysical data from radio pulsars to establish upper limits on the magnetoelectric parameters magnitude. In particular, by using dispersion measure and rotation measure data from five pulsars, we constrain the magnitude of the chiral parameter to the order of ${10}^{-16}$ and ${10}^{-22}$, respectively.

Following the approach of Harutyunyan et al. [Generalized relativistic second-order dissipative hydrodynamics: Coupling different rank tensors, Ann. Phys. (Amsterdam) 481, 170159 (2025)], where additional second-order contributions from nonlocal corrections due to two-point correlation functions of tensors of different ranks at distinct spacetime points were first derived, we similarly employ the nonequilibrium statistical operator method to extend this framework to include spin degrees of freedom. In addition to obtaining analogous extra second-order terms in the shear stress tensor, bulk viscous pressure, and charge diffusion currents resulting from such contributions, we further derive additional second-order terms originating from the same mechanism in the charge diffusion currents, rotational stress tensor, and the boost heat vector. Furthermore, we express all transport coefficients represented by two-point or three-point correlations in terms of retarded Green’s functions.

One of the most notable aspects of quantum systems is that their components can exhibit correlations much stronger than those allowed by classical physics. Two examples of quantum correlations are quantum entanglement and Bell nonlocality, but generally there is a hierarchy of many types of quantum correlations. Among these correlations, Bell nonlocality holds a special place because it plays a dual role in distinguishing theories where local realism is a valid description. A Bell test, which is a test of local realism, typically needs to be augmented with assumptions to address possible loopholes in the experimental setup. In this work, we study Bell tests in experiments in which the detector reports the correct outcome with a specified probability. This mirrors the situation at high-energy colliders, where particle spins are not measured directly but inferred from the angular distributions of their decay products. We show that, in this setup, a test of local realism is not possible. Quantum correlations, however, are still present, measurable, and informative in high-energy colliders. These correlations are the building blocks of the interesting, developing quantum information science program at high-energy colliders. The measurements of entanglement by the ATLAS and CMS experiments are the first steps in this initiative.

In this work we consider the calculation of the imaginary part of the dispersion relations of the propagating modes in a model of a charged scalar Bose-Einstein (BE) condensate, as well as the contribution to the imaginary part of the longitudinal component of the photon polarization tensor and the dielectric constant. In that model, two modes correspond to the transverse photon polarizations, while the other two modes are combinations of the longitudinal photon and the massive scalar field, which we denote as the ($\pm$) modes. The dispersion relations of the transverse modes have the usual form for transverse photons in a plasma, and we do not consider them here any further. In a previous work we determined the real part of the dispersion relations of the ($\pm$) modes, as well as the real part of the longitudinal component of the polarization tensor and dielectric constant, which have some unique features. In the appropriate limit, those results reproduce the results obtained for the dielectric constant and dispersion relation in nonrelativistic models of the BE condensation of charged scalars. Here we determine, in the same model, their imaginary part. The results can be useful in physical contexts involving the electrodynamics of a charged scalar BE condensate, and can serve as benchmark results for further exploration.

In this article, we study the rare decay process in which a Higgs boson decays into a $Z$ boson and a photon. In the first part of the paper, we analyze the Standard Model (SM) contributions to the corresponding decay width, including the full leading-order result, two-loop $O({\alpha }_s)$ QCD corrections, and the recently reported two-loop $O(\alpha )$ electroweak corrections, evaluated under four different $\alpha$ renormalization schemes. The dependence on the Higgs boson mass is studied within the experimentally allowed range reported by the LHC. In the considered schemes, a non-negligible variation of about 4% is found when the mass is varied within its current experimental uncertainty. In the second part of the paper, we analyze the leading-order contributions to the same process within the minimal supersymmetric Standard Model (MSSM). The spectrum of soft SUSY-breaking parameters and SUSY particle masses at the electroweak scale, which enter the computation of the one-loop amplitudes contributing to the decay width, is obtained by evolving the grand unified theory (GUT)-scale parameters of a radiatively driven natural supersymmetry (RNS) model with nonuniversal Higgs boson masses. Variations of the RNS parameters can enhance the average SM prediction by up to $\sim 20\%$, reaching a value of $\sim 7.5\mathrm{keV}$, while still satisfying the Higgs boson mass constraint. However, this comes at the cost of allowing a moderately large fine-tuning parameter, with values exceeding 100, thereby placing the model outside its most natural parameter region. The predicted decay width in the RNS scenario is closer to the recent ATLAS RUN $2+3$ combined measurement than the average SM expectation.

Quark and gluon scalar densities, $⟨\overline{\psi }\psi ⟩$ and $⟨F^2⟩$, reflect the degree of scale-invariance violations in $\mathrm{SU}(N)$ gauge theories with fundamental quarks. It is known that $⟨\overline{\psi }\psi ⟩$ can be usefully scale-decomposed via the spectral density $\rho (\lambda )$ of Dirac modes. Here, we give such formula for $⟨F^2⟩$, which reveals that the gluon condensate is a strictly UV quantity. For the recently found IR phase [1,2], where the infrared (IR) degrees of freedom separate out and become independent of the system’s bulk, it implies that $⟨F^2⟩$ due to this IR part vanishes. Its glue, thus, does not contribute to the scale anomaly of the entire system and is, in this sense, scale invariant consistently with the original claim. Associated formulas are used to define the IR decoupling of glue, which may serve as an alternative indicator of IR phase transition. Using the simplest form of coherent lattice QCD, we express the effective action of full QCD entirely via Dirac spectral density.

We investigate renormalon ambiguities in quasiparton distribution functions (quasi-PDFs) defined using gradient-flowed fields. Focusing on both ultraviolet (UV) and infrared (IR) renormalons, we perform an explicit calculation of bubble chain diagrams to analyze their dependence on the flow time. We find that the gradient flow eliminates UV renormalon in quasi-PDFs. In the small flow-time expansion, the linear renormalons cancel exactly between the matching kernel and the $\overline{\mathrm{MS}}$ quasi-PDF. Meanwhile, IR renormalons persist but are modified at finite flow time. The deformation of the renormalon structure induced by the gradient flow suggests an altered infrared behavior, with enhanced contributions from higher-twist effects even at small flow time.

We set up a numerical S-matrix bootstrap problem to rigorously constrain bound-state couplings given by the residues of poles in elastic amplitudes. We extract upper bounds on these couplings that follow purely from unitarity, crossing symmetry, and the Roy equations within their proven domain of validity. First we consider amplitudes with a single spin-0 or spin-2 bound state, both with or without a self-coupling. Subsequently we investigate amplitudes with the spectrum of bound states corresponding to the estimated glueball masses of pure $SU(3)$ Yang-Mills. In the latter case the “glue-hedron,” the space of allowed couplings, provides a first-principles constraint for future lattice estimates.

The Koba-Nielsen-Olesen (KNO) scaling of hadron multiplicity distributions, empirically confirmed to hold approximately in $e^{+}{e}^{-}$ collisions and deep inelastic scattering, has been observed to be violated in hadron-hadron collisions. In this work, we show that the universality of KNO scaling can be extended to hadron-hadron collisions when restricted to QCD jets. We present a comprehensive study of KNO scaling in QCD jets produced in proton-proton collisions at the LHC. Using perturbative QCD calculations in the double logarithmic approximation and pythia simulations, we find that KNO scaling approximately holds for both quark and gluon jets across a broad jet $p_T$ range, from 0.1 to 2.5 TeV, at both the parton and hadron levels. Especially, we highlight characteristic differences between the KNO scaling functions of quark and gluon jets, with the quark-jet scaling function lying above that of gluon jets at both low and high multiplicities. This distinction is essential for interpreting inclusive jet data at the LHC. Furthermore, we propose direct experimental tests of KNO scaling in QCD jets at the LHC through quark-gluon discrimination using jet substructure techniques, as demonstrated by applying energy correlation functions to pythia-generated data.