We present a formulation of coherent states as of consistent quantum description of classical configurations in the Becchi-Rouet-Stora-Tyutin (BRST)-invariant quantization of electrodynamics. The quantization with proper gauge-fixing is performed on the vacuum of the theory, whereas other backgrounds are obtained as BRST-invariant coherent states. One of the key insights is the possibility of constructing the coherent states of pure-gauge configurations. This provides a coherent state understanding of topologically nontrivial configurations in gauge theories and makes a number of features, such as the suppression of transitions between topologically distinct sectors, very transparent at full quantum level. As an example, we construct the Nielsen-Olesen string as a BRST-invariant coherent state. The Abelian pure-gauge configurations can also be viewed as useful analogs for a set of space-times related by coordinate reparametrizations in general relativity.

We analyze all possible symmetry reductions of Lagrangians that yield fully equivalent field equations for any 4-dimensional metric theory of gravity. Specifically, we present a complete list of infinitesimal group actions obeying the principle of symmetric criticality, identify the corresponding invariant metrics (and $l$-chains), discuss relations among them, and analyze simplifications allowed by the residual diffeomorphism group and Noether identities before and after variation of the reduced Lagrangian. We employ rigorous treatment of the symmetry reduction by Fels and Torre and use the Hicks classification of infinitesimal group actions by means of Lie algebras pairs of isometries and their isotropy subalgebras. The classification is recast in the coordinates in which the well-known symmetries and geometries are easily recognizable and relatable to each other. The paper is accompanied by a code for the symmetry reduction of Lagrangians that we developed in xact package of Mathematica.

Next-generation ground-based gravitational wave observatories will observe mergers of intermediate-mass black holes (IMBHs) out to high redshift. Such IMBHs can form through runaway tidal encounters in the cores of dense stellar clusters. In this paper, we ask if the gravitational wave observation of a single merger event between two IMBHs, occurring in the aftermath of the coalescence of the clusters in which they formed, can be used to infer the properties of their host clusters, such as mass, redshift, and half-mass radius. We implement an astrophysically motivated analytic model for cluster evolution and IMBH growth, and we perform IMBH binary parameter estimation using a network of three next-generation detectors. We find that inferring the structural properties of clusters in this way is challenging due to model degeneracy. However, the posteriors on the cluster formation redshifts have relatively narrow peaks, and it may still be possible to infer the cluster formation history by measuring a whole population of IMBH binary merger events.

A formulation for the parametric instability of electromagnetic waves in magnetized pair plasma is developed. The linear growth rate of induced Compton scattering is derived analytically for frequencies below the cyclotron frequency for the first time. We identify three modes of density fluctuation: ordinary, charged, and neutral modes. In the charged mode, the ponderomotive force separates charges (electrons and positrons) longitudinally, in contrast to the nonmagnetized case. We also recognize two effects that significantly reduce the scattering rate for waves polarized perpendicular to the magnetic field: (1) the gyroradius effect due to the magnetic suppression of particle orbits and (2) Debye screening effect for wavelengths larger than the Debye length. Applying this to fast radio bursts, we find that these effects facilitate the escape of X-mode waves from the magnetosphere and outflow of a magnetar and neutron star, enabling 100% polarization as observed. Our formulation provides a foundation for consistently addressing the nonlinear interaction of electromagnetic waves with magnetized plasma in astrophysics and laser physics.

We study observational signatures of the hadron-quark crossover in binary-neutron-star mergers by numerical-relativity simulations with various mass configurations. We employ two equations of state (EoSs) for matter consistent with inference from the observational data. In the crossover scenario the EoS is softened in a density realized in binary-neutron-star mergers and is smoothly continued to quark matter. In the phase transition scenario without crossover, the EoS remains stiff and a first-order phase transition takes place in a density out of reach of mergers. A GW170817-like system forms a remnant massive neutron star in both scenarios, and it collapses into a black hole only in the crossover scenario due to the softening while gravitational-wave emission is strong. This difference is clearly reflected in the sudden shutdown of gravitational waves. For a given EoS, the lifetime of the merger remnant is determined primarily by the total mass of the system. Identifying these features in a variety of future events with the next generation of ground-based gravitational-wave detectors will enable us to clarify details of hadron-quark transition. The mass of the accretion disk surrounding the remnant black hole is affected not only by the lifetime of the remnant but also by the mass ratio of the system. Electromagnetic emission associated with the disk outflow will also be useful for detailed investigation of the hadron-quark transition.

The gravitational path integral is usually implemented with a covariant action by analogy with other gauge field theories, but the gravitational case is different in important ways. A key difference is that the integrand has an essential singularity, which occurs at zero lapse where the spacetime metric degenerates. The lapse integration contour required to impose the local time reparametrization constraints must run from $-\infty$ to $+\infty$, yet must not pass through zero. This raises the question: for an application—such as a partition function—where the constraints should be imposed, what is the correct integration contour, and why? We study that question by starting with the reduced phase space path integral, which involves no essential singularity. We observe that if the momenta are to be integrated before the lapse, to obtain a configuration space path integral, the lapse contour should pass below the origin in the complex lapse plane. This contour is also consistent with the requirement that quantum field fluctuation amplitudes have the usual short distance vacuum form, and with obtaining the Bekenstein-Hawking horizon entropy from a Lorentzian path integral.

We study the class of generalized Kerr-Schild (GKS) spacetimes in dimensions $n\ge 3$ and analyze their geometric and algebraic properties in a completely theory-independent setting. First, considering the case of a general null vector $\mathbf{k}$ defined by the GKS metric, we obtain the conditions under which it is geodesic. Assuming $\mathbf{k}$ to be geodesic for the remainder of the paper, we examine the alignment properties of the curvature tensors, namely the Ricci and Weyl tensors. We show that the algebraic types of the curvatures of the full (GKS) geometry are constrained by those of the respective background curvatures, thereby listing all kinematically allowed combinations of the algebraic types for the background and the full geometry. A notable aspect of these results is that, unlike the case of Kerr-Schild (KS) spacetimes, the Weyl types of the GKS spacetimes need not be type $II$ or more special. Then, focusing on the case of an expanding $\mathbf{k}$, we derive the conditions for it to satisfy the optical constraint, extending the previous results of KS spacetimes. We illustrate the general results using the example of (A)dS-Taub-NUT spacetimes in $n=4$, where we also comment on their KS double copy from a GKS perspective. Finally, as an application of our general results, we obtain the full family of GKS spacetimes with a geodesic, expanding, twist-free, and shear-free $\mathbf{k}$, satisfying the vacuum Einstein equations, and identify it with a subset of the higher-dimensional vacuum Robinson-Trautman solutions. In passing, we also determine the subcase of these solutions that manifests the KS double copy.

In Newtonian gravity, it is well known that Kepler’s problem admits no bound solutions in more than three spatial dimensions. This limitation extends naturally to General Relativity, where Tangherlini demonstrated that Schwarzschild black holes in higher dimensions admit no bound timelike geodesics. However, an analogous result for the rotating counterpart of the five-dimensional Tangherlini spacetime—the $d=5$ Myers-Perry black hole—has not yet been established. This work addresses this gap by proving that no bound timelike geodesics exist outside the event horizon of a $d=5$ Myers-Perry black hole, for any choice of spin parameters that avoid naked singularities. With this result in place, we further generalize to null geodesics. It is shown that radially bound null geodesics, which are absent in the four-dimensional Kerr spacetime as established by Wilkins, also cannot exist in the $d=5$ Myers-Perry spacetime. These results complete the geodesic analysis of this spacetime and provide a direct generalization of Wilkins’s classical result to higher dimensions. Specifically, we establish the following theorem: no radially bound timelike nor null geodesics are possible outside the event horizon of a $d=5$ Myers-Perry black hole, regardless of the spin configuration.

We discuss a mechanism of primordial black hole (PBH) formation that does not require specific features in the inflationary potential, revisiting previous literature. In this mechanism, a light spectator field evolves stochastically during inflation and remains subdominant during the post-inflationary era. Even though the curvature power spectrum stays small at all scales, rare perturbations of the field probe a local maximum in its potential, leading to non-Gaussian tails in the distribution of curvature fluctuations, and to copious PBH production. For a concrete axionlike particle (ALP) scenario we analytically determine the distribution of the compaction function for perturbations, showing that it is characterized by a heavy tail, which produces an extended PBH mass distribution. We find the ALP mass and decay constant to be correlated with the PBH mass, for instance, an ALP with a mass $m_a=5.4\times {10}^{14}\mathrm{eV}$ and a decay constant $f_a=4.6\times {10}^{-5}{M}_{\mathrm{Pl}}$ can lead to PBHs of mass $M_{\mathrm{PBH}}={10}^{21}\mathrm{g}$ as the entire dark matter of the universe, and is testable in future PBH observations via lensing in the Nancy Grace Roman Space Telescope and mergers detectable in the Laser Interferometer Space Antenna and Einstein Telescope gravitational wave detectors. We then extend our analysis to mixed ALP and PBH dark matter and Higgs-like spectator fields. We find that PBHs cluster strongly over all cosmological scales, clashing with cosmic microwave background isocurvature bounds. We argue that this problem is shared by all PBH production from inflationary models that depend solely on large non-Gaussianity without a peak in the curvature power spectrum and discuss possible remedies.

A realistic and detailed description of neutrinos in binary neutron star (BNS) mergers is essential to build reliable models of such systems. To this end, we present bns_nurates, a novel open-source numerical library designed for the efficient on-the-fly computation of neutrino interactions, with particular focus on regimes relevant to BNS mergers. bns_nurates targets a higher level of accuracy and realism in the implementation of commonly employed reactions by accounting for relevant microphysics effects on the interactions, such as weak magnetism and mean field effects. It also includes the contributions of inelastic neutrino scattering off electrons and positrons and (inverse) nucleon decays. Finally, it offers a way to reconstruct the neutrino distribution function in the framework of moment-based transport schemes. As a first application, we compute both energy-dependent and energy-integrated neutrino emissivities and opacities for conditions extracted from a BNS merger simulation with m1 transport scheme. We find some qualitative differences in the results when considering the impact of the additional relevant reactions and of microphysics effects. For example, neutrino-electron/positron scattering reactions are important for the energy exchange of heavy-type neutrinos as they do not undergo semileptonic charged-current processes, when ${\mu }^{\pm }$ are not accounted for. Moreover, weak magnetism and mean field effects can significantly modify the contribution of $\beta$ processes for electron-type (anti)neutrinos, increasing at the same time the importance of (inverse) neutron decays. The improved treatment for the reaction rates also modifies the conditions at which neutrinos decouple from matter in the system, potentially affecting their emission spectra.

The indirect detection of dark matter (DM) through its annihilation products is one of the primary strategies for DM detection. One of the least constrained classes of models is neutrinophilic DM, because the annihilation products, weakly interacting neutrinos, are challenging to observe. Here, we consider a scenario where MeV-mass DM exclusively annihilates to the third neutrino mass eigenstate, which is predominantly of tau and muon flavor. In such a scenario, the potential detection rate of the neutrinos originating from the DM annihilation in our Galaxy in the conventional detectors would be suppressed by up to approximately two orders of magnitude. This is because the best sensitivity of such detectors for neutrinos with energies below approximately 100 MeV is for electron neutrino flavor. In this work, we highlight the potential of large-scale DM detectors in uncovering such signals in the tens of MeV range of DM masses. In addition, we discuss how coincident signals in direct detection DM experiments and upcoming neutrino detectors such as DUNE, Hyper-Kamiokande, and JUNO could provide new perspectives on the DM problem.

The Beryllium Electron capture in Superconducting Tunnel junctions (BeEST) experiment searches for evidence of heavy neutrino mass eigenstates in the nuclear electron capture decay of ${}^7\mathrm{Be}$ by precisely measuring the recoil energy of the ${}^7\mathrm{Li}$ daughter. In Phase III, the BeEST experiment has been scaled from a single superconducting tunnel junction (STJ) sensor to a 36-pixel array to increase sensitivity and mitigate gamma-induced backgrounds. Phase III also uses a new continuous data acquisition system that greatly increases the flexibility for signal processing and data cleaning. We have developed procedures for signal processing and spectral fitting that are sufficiently robust to be automated for large datasets. This article presents the optimized procedures before unblinding the majority of the Phase III dataset to search for physics beyond the standard model.

Double- and single-differential cross sections for inclusive charged-current ${\nu }_{\mu }$-nucleus scattering are reported for the kinematic domain 0 to $2\mathrm{GeV}/c$ in three-momentum transfer and 0 to 2 GeV in available energy, at a mean ${\nu }_{\mu }$ energy of 1.86 GeV. The measurements are based on an estimated 995,760 ${\nu }_{\mu }$ charged-current (CC) interactions in the scintillator medium of the NOvA Near Detector. The subdomain populated by 2-particle-2-hole (2p2h) reactions is identified by the cross section excess relative to predictions for ${\nu }_{\mu }$-nucleus scattering that are constrained by a data control sample. Models for 2-particle-2-hole processes are rated by ${\chi }^2$ comparisons of the predicted-versus-measured ${\nu }_{\mu }$ CC inclusive cross section over the full phase space and in the restricted subdomain. Shortfalls are observed in neutrino generator predictions obtained using the theory-based València and SuSAv2 2p2h models.

In ultrarelativistic heavy ion collisions at the LHC, each nucleus acts a sources of high-energy real photons that can scatter off the opposing nucleus in ultraperipheral photonuclear ($\gamma +A$) collisions. Hard scattering processes initiated by the photons in such collisions provide a novel method for probing nuclear parton distributions in a kinematic region not easily accessible to other measurements. ATLAS has measured production of dijet and multijet final states in ultraperipheral $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ using a dataset recorded in 2018 with an integrated luminosity of $1.72{\mathrm{nb}}^{-1}$. Photonuclear final states are selected by requiring a rapidity gap in the photon direction; this selects events where one of the outgoing nuclei remains intact. Jets are reconstructed using the anti-$k_{\mathrm{t}}$ algorithm with radius parameter, $R=0.4$. Triple-differential cross sections, unfolded for detector response, are measured and presented using two sets of kinematic variables. The first set consists of the total transverse momentum ($H_{\mathrm{T}}$), rapidity, and mass of the jet system. The second set uses $H_{\mathrm{T}}$ and particle-level nuclear and photon parton momentum fractions, $x_{\mathrm{A}}$ and $z_{\gamma }$, respectively. The results are compared with leading-order perturbative QCD calculations of photonuclear jet production cross sections, where all leading order predictions using existing fits fall below the data in the shadowing region. More detailed theoretical comparisons will allow these results to strongly constrain nuclear parton distributions, and these data provide results from the LHC directly comparable to early physics results at the planned Electron-Ion Collider.

Kerr-Newman black holes in a de Sitter (dS) space have the limit of rotating Nariai black holes with the near-horizon geometry of a warped ${\mathrm{dS}}_3\times {\mathrm{S}}^1/Z_2$ when the black hole horizon and the cosmological horizon coincide or approach close to each other. We study the rotation effect on the spontaneous emission of charges in the near-extremal rotating charged Nariai black hole and compare it to those from the near-extremal Nariai black hole in [C.-M. Chen et al., Phys. Rev. D 110, 085020 (2024)] and near-extremal Kerr-Newman black hole in de Sitter space in [C.-M. Chen and S. P. Kim, Eur. Phys. J. C 83, 219 (2023)]. In strong contrast to the near-extremal Kerr-Newman black hole in dS space, the near-extremal rotating Nariai black hole also has an exponential amplification for the emission of high-energy charges, which becomes catastrophic regardless of angular momentum when two horizons coincide. The radius of rotating Nariai black holes monotonically increases as the angular momentum and charge of black holes increase, which gives a weaker electric field on the horizon than Nariai black holes. Thus, the angular momentum of black holes that drags particles on the horizon decreases the mean number of charges by a factor not by an order. We observe a catastrophic emission of boson condensation for charges with an effective energy equal to the chemical potential in the spacelike outer region of the cosmological horizon. Remarkably, the Schwinger emission of charges in the standard particle model may prevent the rotating Nariai black holes from evolving into spacetimes with a naked singularity when the angular momentum is close to the allowed maximum, which Nariai black holes cannot avoid.

The response of a gravitational-wave (GW) interferometer is spatially modulated and is described by two antenna patterns, one for each polarization state of the waves. The antenna patterns are derived from the shape and size of the interferometer, usually under the assumption that the interferometer size is much smaller than the wavelength of the gravitational waves (long wavelength approximation, LWA). This assumption is well justified as long as the frequency of the gravitational waves is well below the free spectral range (FSR) of the Fabry-Perot cavities in the interferometer arms as it happens for current interferometers ($\mathrm{FSR}=37.5\mathrm{kHz}$ for the LIGO interferometers and $\mathrm{FSR}=50\mathrm{kHz}$ for Virgo and KAGRA). However, the LWA can no longer be taken for granted with third-generation instruments (Einstein Telescope, Cosmic Explorer and LISA) because of their longer arms. This has been known for some time, and previous analyses have mostly been carried out in the frequency domain. In this paper, we explore the behavior of the frequency-dependent antenna patterns in the time domain and in the time-frequency domain, with specific reference to the searches of short GW transients. We analyze the profound changes in the concept of Dominant Polarization Frame, which must be generalized in a nontrivial way, we show that the conventional likelihood-based analysis of coherence in different interferometers can no longer be applied as in current analysis pipelines, and that methods based on the null stream in triangular (60°) interferometers no longer work. Overall, this paper establishes methods and tools that can be used to overcome these difficulties in the unmodeled analysis of short GW transients.

In this article, we focus on symmetric teleparallel gravity, a modification of general relativity where gravity is described by the nonmetricity of an affine connection, whose curvature and torsion vanish. In these theories, the fundamental variables are the metric and an affine connection. Starting from the coincident gauge, a system of coordinates for which the affine connection coefficients vanish, we derive the most general connection for a spherically symmetric and stationary spacetime. We then derive the field equations in a specific class of symmetric teleparallel theories, the so-called newer general relativity. This theory is constructed from the five possible quadratic scalars of nonmetricity. We find two families of vacuum solutions that correspond to some exotic objects and we study their properties. In particular, we investigate the possibility of having a traversable wormhole, we compute the Komar mass, we discuss the conditions for asymptotic flatness, the existence of singularities, the radial motion and bound orbits of particles around these objects, the light deflection, as well as the causal structure of these spacetimes.

In the early Universe, large-scale flows were omnipresent, and the flow collisions produced sheets and filaments. This phenomenon occurs for particle dark matter, as it also does for wave dark matter. However, for the latter, these sheets and filaments are the modulations of even finer-scale, large-amplitude interference fringes. This work aims to investigate the instability of the interference fringes arising from colliding waves. Two colliding streams in classical collisionless fluid systems can often produce small-scale unstable oscillations with a finite complex frequency, a situation identified as propagating instabilities. In fact, propagating unstable oscillations have never been observed in the conventional quantum system due to its being Sturm-Liouville property. For example, quantum fluid equations with Madelung variables only exhibit either Jeans instability, a purely growing unstable mode, or stable oscillations, for which the squared frequency ${\omega }^2$ is real. Despite that, this work discovers that quantum interference fringes can indeed generate propagating unstable oscillations with a complex ${\omega }^2$ when the gravitational feedback perturbation is included. The presence of local density nulls in the background density is shown to be the necessary condition for such an instability. We establish a phase diagram separating the propagating instability, Jeans instability, and stable oscillation regions, verified by computer simulations. Generally speaking, Jeans instabilities tend to occur for long-wave density perturbations as expected; propagating instabilities, on the other hand, tend to occur for short density waves with wavelengths comparable to the fringe size, i.e., near the center of the Bloch zone. Finally, both instabilities diminish for very low density fringes. The propagating unstable fluctuation may possibly collapse into halos of small sizes, potentially seeding the formation of protoglobular clusters.

Reconstructing the properties of the astrophysical population of binary compact objects in the universe is a key science goal of gravitational wave detectors. This goal is hindered by the finite strain, frequency sensitivity and observing time of current and future detectors. This implies that we can in general observe only a selected subset of the underlying population, with limited event statistics, and also nontrivial observational uncertainties in the parameters of each event. In this work, we will focus on observations of massive black hole binaries with the Laser Interferometer Space Antenna (LISA). If these black holes grow from population III star remnants (“light seeds”), a significant fraction of the binary population at low masses and high redshift will be beyond LISA’s observational reach; thus, selection effects have to be accounted for when reconstructing the underlying population. Here we propose an iterative, kernel density estimation-based nonparametric method, in order to tackle these statistical challenges in reconstructing the astrophysical population distribution from a finite number of observed signals over total mass and redshift. We test the method against a set of simulated LISA observations in a light seed formation scenario. We find that our approach is successful at reconstructing the underlying astrophysical distribution in mass and redshift, except in parameter regions where zero or order(1) signals are observed.