We introduce a family of solutions of Einstein’s gravity minimally coupled to an anisotropic fluid, describing asymptotically flat black holes with “hair” and a regular horizon. These spacetimes can describe the geometry of galaxies harboring supermassive black holes, and are extensions of Einstein clusters to include horizons. They are useful to constrain the environment surrounding astrophysical black holes, using electromagnetic or gravitational-wave observations. We compute the main properties of the geometry, including the corrections to the ringdown stage induced by the external matter and fluxes by orbiting particles. The leading order effect to these corrections is a gravitational-redshift, but gravitational-wave propagation is affected by the galactic potential in a nontrivial way, and may be characterized with future observatories.

Recently, the Baksan Experiment on Sterile Transitions (BEST) has presented results [1] confirming the gallium anomaly—a lack of electron neutrinos ${\nu }_e$ at calibrations of SAGE [2,3] and GALLEX [4]—at the statistical significance exceeding $5\sigma$. This result is consistent with explanation of the gallium anomaly as electron neutrino oscillations into a sterile neutrino, ${\nu }_s$. Within this explanation, the BEST experiment itself provides the strongest evidence for the sterile neutrino among all the previous anomalous results in the neutrino sector. We combine the results of gallium experiments with searches for sterile neutrinos in reactor antineutrino experiments (assuming $CPT$ conservation in the $3+1$ neutrino sector). While the “gallium” best-fit point in the model parameter space (sterile neutrino mass squared $m_{{\nu }_s}^2\approx 1.25{\mathrm{eV}}^2$, sterile-electron neutrino mixing ${\sin }^{2}2\theta \approx 0.34$) is excluded by these searches, a part of the BEST-favored $2\sigma$ region with $m_{{\nu }_s}^2>5{\mathrm{eV}}^2$ is consistent with all of them. Remarkably, the regions advertised by anomalous results of the NEUTRINO-4 experiment [5] overlap with those of the BEST experiment: the best-fit point of the joint analysis is ${\sin }^{2}2\theta \approx 0.38$, $m_{{\nu }_s}^2\approx 7.3{\mathrm{eV}}^2$, and the favored region will be explored by the KATRIN experiment [6]. The sterile neutrino explanation of the BEST results would suggest not only the extension of the Standard Model of particle physics but also either serious modifications of the Standard Cosmological Model and Solar Model, or a specific modification of the sterile sector needed to suppress the sterile neutrino production in the early Universe and in the Sun.

We investigate a concrete scenario of a light scalar with a mass around 1 MeV which can be connected to the origin of neutrino masses and simultaneously survive current bounds on relativistic degrees of freedom in the early universe. A feeble coupling to the Standard Model neutrinos can relax stringent bounds on the decays to photons inferred from the measured value of $N_{\mathrm{eff}}$. Interestingly, we find that such a scalar whose diphoton coupling is generated by a tree-level coupling to the muon of similar strength as that of the Standard Model Higgs boson can simultaneously explain the longstanding discrepancy in the measured value of the muon magnetic moment. We present a possible ultraviolet (UV) completion of this scenario providing a link between new physics in the early universe and the generation of neutrino masses.

We investigate the weak decays of ${\overline{B}}_s^0$ and ${\mathrm{\Lambda }}_b$ to charm hadrons based on the dynamical supersymmetry between the $\overline{s}$ quark and the $ud$ diquark. We derive a new sum rule relating the decay rates of the processes ${\overline{B}}_s^0\to D_s^{+}{P}^{-}$, ${\overline{B}}_s^0\to D_s^{*+}{P}^{-}$, and ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c{P}^{-}$, where $P^{-}$ is a negatively charged meson, such as ${\pi }^{-}$ and $K^{-}$. It is found that the observed decay rates satisfy the sum rule very well. This implies that the supersymmetry between the $\overline{s}$ quark and the $ud$ diquark is also seen in the wave functions of the heavy hadrons and suggests that the $ud$ diquark can be regarded as a valid effective constituent for heavy hadrons.

With a key improvement, the auxiliary mass flow method is now able to compute Feynman integrals encountered in cutting-edge collider processes. We have successfully applied it to compute some integrals involved in two-loop electroweak corrections to $e^{+}{e}^{-}\to HZ$, two-loop QCD corrections to $3j$, $W/Z/H+2j$, $t\overline{t}H$ and $4j$ production at hadron colliders, and three-loop QCD corrections to $t\overline{t}$ production at hadron colliders, all of which are crucial for precision frontier in collider physics in the following decade. Our results are important building blocks and benchmarks for future studies of these processes.

We present the first measurement of the single-differential ${\nu }_e+{\overline{\nu }}_e$ charged-current inclusive cross sections on argon in electron or positron energy and in electron or positron scattering angle over the full range. Data were collected using the MicroBooNE liquid argon time projection chamber located off axis from the Fermilab neutrinos at the main injector beam over an exposure of $2.0\times {10}^{20}$ protons on target. The signal definition includes a 60 MeV threshold on the ${\nu }_e$ or ${\overline{\nu }}_e$ energy and a 120 MeV threshold on the electron or positron energy. The measured total and differential cross sections are found to be in agreement with the genie, nuwro, and gibuu neutrino generators.

We establish that boundary degrees of freedom associated with a generic codimension one null surface in $D$-dimensional pure Einstein gravity naturally admit a thermodynamical description. We expect the null surface thermodynamics to universally follow as a result of the diffeomorphism invariance of the theory, not relying on other special features of the null surface or the gravity theory. Using standard surface charge analysis and covariant phase-space method, we formulate laws of null surface thermodynamics which are local equations over an arbitrary null surface paralleling local versions of the zeroth- and first laws and the Gibbs-Duhem equation. This thermodynamical system is generally an open system and can be closed only when there is no flux of gravitons through the null surface. Our analysis extends the usual black hole thermodynamics to a universal feature of any area element on a generic null surface. We discuss the relevance of our study for the membrane paradigm and black hole microstates.

We present the first numerical calculation of the 4D Euclidean spin foam vertex amplitude for vertices with hypercubic combinatorics. Concretely, we compute the amplitude for coherent boundary data peaked on cuboid and frustum shapes. We present the numerical algorithms to explicitly compute the vertex amplitude and compare the results in different cases to the semiclassical approximation of the amplitude. Overall we find good qualitative agreement of the amplitudes and evidence of convergence of the asymptotic formula to the full amplitude already at fairly small spins, yet also differences in the frequency of oscillations and a phase shift absent in the 4-simplex case. However, due to rapidly growing numerical costs, we cannot reach sufficiently high spins to prove agreement of both amplitudes. Lastly, this setup allows us to explore nonuniform vertex amplitudes, where some representations are small while others are large; we find indications that scenarios might exist in which the semiclassical amplitude is a valid approximation even if some spins remain small. This suggests that the transition of the quantum to the semiclassical regime (for a single vertex amplitude) is intricate.

Mass currents in astrophysics generate gravitomagnetic fields of enormous complexity. Gravitomagnetic helicity, in direct analogy with magnetic helicity, is a measure of entwining of the gravitomagnetic field lines. We discuss gravitomagnetic helicity within the gravitoelectromagnetic (GEM) framework of linearized general relativity. Furthermore, we employ the spacetime curvature approach to GEM in order to determine the gravitomagnetic helicity for static observers in Kerr spacetime.

A wave pulse (be it a gravitational wave or a light wave) undergoes anomalous dispersion in a vacuum in flat spacetimes with an even number of spatial dimensions even if all the frequencies move at the same speed. Such an anomalous dispersion does not occur in spacetimes with an odd number of spatial dimensions. We study various gravity theories and show that dispersion-free propagation is possible in even number of spatial dimensions if the background is not the Minkowski but the de Sitter spacetime and the gravity theory is massive gravity with a tuned mass in terms of the cosmological constant. Mass and the cosmological constant conspire to get rid of the anomalous dispersion and restore Huygens’s principle.

For a stationary, axisymmetric, asymptotically flat, ultracompact [i.e., containing light rings (LRs)] object, with a ${\mathbb{Z}}_2$ north-south symmetry fixing an equatorial plane, we establish that the structure of timelike circular orbits (TCOs) in the vicinity of the equatorial LRs, for either rotation direction, depends exclusively on the radial stability of the LRs. Thus, an unstable LR delimits a region of unstable TCOs (no TCOs) radially above (below) it; a stable LR delimits a region of stable TCOs (no TCOs) radially below (above) it. Corollaries are discussed for both horizonless ultracompact objects and black holes. We illustrate these results with a variety of exotic stars examples and non-Kerr black holes, for which we also compute the efficiency associated with converting gravitational energy into radiation by a material particle falling under an adiabatic sequence of TCOs. For most objects studied, it is possible to obtain efficiencies larger than the maximal efficiency of Kerr black holes, i.e., larger than 42%.

We consider disformal transformations in a subclass of Horndeski theory in which a scalar field is kinetically coupled to the Einstein tensor. We apply a disformal transformation on a seed hairy black hole solution of this theory and we show that there is a transition of a black hole to a wormhole. We also show that the null energy condition is violated in the wormhole configuration and we study the stability of the wormhole solution by calculating the time evolution of scalar perturbations in this geometry.

We show that Thurston geometries are solutions to a large class of 3D quadratic curvature theories, where new massive gravity—which was studied by Flores-Alfonso et al. [Phys. Rev. Lett. 127, 061102 (2021)]—is a special case.

In this work, we consider the burst signal of the dark photon, the hypothetical vector boson of the $U(1{)}_B$ or $U(1{)}_{B-L}$ gauge group, generated by a compact binary star system. The absence of the signal in the laser interferometer puts bounds on the coupling constant $\epsilon$ to the ordinary matter. It turns out that if the dark photon is massless, ${\epsilon }^2$ is on the order of ${10}^{-37}–{10}^{-33}$ at most; in the massive case, the upper bound of ${\epsilon }^2$ is about ${10}^{-38}–{10}^{-31}$ in the mass range from ${10}^{-19}$ to ${10}^{-11}\mathrm{eV}$. These are the first bounds derived from the interferometer observations independent of the assumption of dark photons being dark matter.

It is well known that general relativity is an effective theory of gravity at low energy scale, and actually quantum effects cannot be ignored in the strong-field regime. As a strong gravitational object, a black hole plays a key role in testing the quantum effects of gravity in the strong-field regime. In this paper, we focus on the black hole in effective loop quantum gravity and investigate what the influences are of the quantum effects on the weak and strong bending angles of light rays. We find that this black hole could be a Schwarzschild black hole, a regular black hole, a one-way traversable wormhole, or a two-way traversable wormhole for the different values of the quantum parameter, and the strong bending angle for this compact object exhibits two different divergent behaviors, i.e., the logarithmic divergence and nonlogarithmic divergence. There is a series of relativistic images on both sides of the optical axis. Only the outermost one can be resolved as a single image, and all others are packed together at the limiting angular position. It is interesting to note that the angular separation between the outermost relativistic image and the others initially increases and then decreases as the quantum parameter increases, indicating that there is a maximum in the angular separation. The maximum is reached after the black hole becomes a wormhole, which can be taken as a signal for the formation of the wormhole. Moreover, the limiting angular position decreases as the quantum parameter increases but a little bounce occurs after the formation of the wormhole, and the relative magnification in magnitudes first decreases and then increases as the quantum parameter increases.

We investigate the galaxy bispectrum induced by the nonlinear gravitational evolution as a possible probe to constrain degenerate higher-order scalar tensor (DHOST) theories. We find that the signal obtained from the leading kernel of second-order density fluctuations is partially hidden by the uncertainty in the nonlinear galaxy bias, and that the kernel of second-order velocity fields instead provides unbiased information on the modification of gravity theory. Based on this fact, we propose new phenomenological time-dependent functions, written as a combination of the coefficients of the second-order kernels, which is expected to trace the higher-order growth history. We then present approximate expressions for these variables in terms of parameters that characterize the DHOST theories. We also show that the resultant formulas provide new constraints on the parameter space of the DHOST theories.

Near-extremal primordial black holes stable over cosmological timescales may constitute a significant fraction of the dark matter. Due to their charge, the coalescence rate of such black holes is enhanced inside clusters, and the nonextremal merger remnants are prone to Hawking evaporation. We demonstrate that if these clusters of near-extremal holes contain a sufficient number of members to survive up to low redshift, the hard photons from continued evaporation begin to dominate the high energy diffuse background. We find that the diffuse photon flux can be observed for a monochromatic mass spectrum of holes lighter than about ${10}^{12}\mathrm{g}$. We place upper bounds on their abundance respecting the current bounds set by gamma ray telescopes. Furthermore, the gravitational wave background induced at the epoch of primordial black hole formation may be detectable by future planned and proposed ground-based and space-borne gravitational wave observatories operating in the mHz to kHz frequency range and can be an important tool for studying light charged primordial black holes over masses in the range of ${10}^{12}–{10}^{19}\mathrm{g}$.

We derive the empirical formulas for the neutron star mass and gravitational redshift as a function of the central density and specific combination of the nuclear saturation parameters, which are applicable to the stellar models constructed with the central density up to threefold nuclear saturation density. Combining both empirical formulas, one also estimates the neutron star radius. In practice, we find that the neutron star mass (radius) can be estimated within $\sim 10\%$ (a few percent) accuracy by comparing the mass and radius evaluated with our empirical formulas to those determined with the specific equation of state. Since our empirical formulas directly connect the neutron star mass and radius to the nuclear saturation parameters, one can discuss the neutron star properties with the specific values of nuclear saturation parameters constrained via nuclear experiments.

Axionlike particles (ALPs) are a class of hypothetical pseudoscalar particles which feebly interact with ordinary matter. The hot plasma of core-collapse supernovae is a possible laboratory to explore physics beyond the standard model including ALPs. Once produced, some of the ALPs can be absorbed by the supernova matter and affect energy transfer. In this study, we calculate the ALP emission in core-collapse supernovae and the backreaction on supernova dynamics consistently. It is found that the stalled bounce shock can be revived if the coupling between ALPs and photons is as high as $g_{a\gamma }\sim {10}^{-9}{\mathrm{GeV}}^{-1}$ and the ALP mass is 40–400 MeV. Most of the models result in more energetic explosions than the average observed supernova. While this can be used to place constraints on those ALPs, long-term simulations across multiple progenitors need to be further investigated to place robust limits.

Threshold and infrared divergences are studied as possible mechanisms of particle production and are compared to the usual decay process in a model quantum field theory from which generalizations are obtained. A spectral representation of the propagator of the decaying particle suggests that decay, threshold, and infrared singularities while seemingly different phenomena are qualitatively related. We implement a nonperturbative dynamical resummation method to study the time evolution of an initial state. It is manifestly unitary and yields the asymptotic state and the distribution function of produced particles. Whereas the survival probability in a decay process falls off as $e^{-\mathrm{\Gamma }t}$, for threshold and infrared divergent cases it falls off instead as $e^{-\sqrt{t/t^{*}}}$ and $t^{-\mathrm{\Delta }}$, respectively, with $\mathrm{\Gamma },\mathrm{\Delta }\propto (\text{coupling}{)}^2$, whereas $1/t^{*}\propto (\text{coupling}{)}^4$. Despite the different decay dynamics, the asymptotic state is qualitatively similar: a kinematically entangled state of the daughter particles with a distribution function which fulfills the unitarity condition and is strongly peaked at energy conserving transitions but broadened by the “lifetime” $1/\mathrm{\Gamma };t^{*}$ for usual decay and threshold singularity, whereas it scales with the anomalous dimension $\mathrm{\Delta }$ for the infrared singular case. Threshold and infrared instabilities are production mechanisms just as efficient as particle decay. If one of the particles is in a dark sector and not observed, the loss of information yields an entanglement entropy determined by the distribution functions and increases upon unitary time evolution.