OJ 287 is a blazar thought to be a binary system containing a $\simeq 18\mathrm{billion}$ solar mass primary black hole accompanied by a $\simeq 150\mathrm{million}$ solar mass secondary black hole in an eccentric orbit, which triggers electromagnetic flares twice in every $\simeq 12\mathrm{year}$ orbital period when it traverses the accretion disk of the primary. The times of these emissions are consistent with the predictions of general relativity calculated to the 4.5th post-Newtonian order. The orbit of the secondary black hole samples the gravitational field at distances between $\mathcal{O}(10)$ and $\mathcal{O}(50)$ Schwarzschild radii around the primary, and hence is sensitive to the possible presence of a dark matter spike around it. We find that the agreement of general-relativistic calculations with the measured timings of flares from OJ 287 constrains the mass of such a spike to $\lesssim 3\%$ of the primary mass.

Out-of-equilibrium reactions between different particle species are the main processes contributing to bulk viscosity in neutron stars. In this work, we numerically compare three different approaches to the modeling of bulk viscosity: the multicomponent fluid with reacting particle species and two bulk stress formalism based on the Müller-Israel-Stewart theory, namely the Hiscock-Lindblom and the Maxwell-Cattaneo models, whose flux-conservative formulation in radial gauge-polar slicing coordinates and spherical symmetry is derived in a companion paper. To our knowledge, this is the first time that a neutron star is simulated with the complete Hiscock-Lindblom model of bulk viscosity. We find that the Hiscock-Lindblom and Maxwell-Cattaneo models are good approximations of the multicomponent fluid for small perturbations and when the nonequilibrium equation of state of the fluid depends on only one independent particle fraction. For more than one independent particle fraction and for large perturbations, the bulk stress approximation is still valid but less accurate. In addition, we include the energy loss due to the luminosity of the reactions in the bulk stress formulation. We find that the energy loss due to bulk viscosity has a larger effect on the dynamics than the bulk stress or the variation in particle composition per se. The new one-dimensional, general-relativistic hydrodynamic code developed for this work, hydro-bulk-1D, is publicly available.

The faithful inclusion of the effects of bulk viscosity induced by the presence of chemical reactions is an important issue for simulations of core-collapse supernovae, binary neutron star mergers, and neutron star oscillations, where particle abundances are locally pushed out of chemical equilibrium by rarefaction and compression of the fluid elements. In this work, we discuss three different approaches that can be used to implement bulk viscosity in general relativistic hydrodynamic simulations of neutron stars: the exact multicomponent reacting fluid, and two Müller-Israel-Stewart theories, namely the second-order Hiscock-Lindblom model and its linear limit, the Maxwell-Cattaneo model. After discussing the theory behind the three approaches, we specialize their dynamics equations to spherical symmetry in the radial gauge-polar slicing (i.e., Schwarzschild) coordinates. We also discuss a particular choice for the equation of state of the fluid and the associated neutrino emission rates, which are used in a companion paper for the numerical comparison of the three frameworks, and we obtain the effective sound speed for the Hiscock-Lindblom theory in the nonlinear regime.

We consider the prospects for future ultrahigh energy cosmic ray and neutrino observations to constrain the evolution of sources producing a proton flux above 10 EeV ($1\mathrm{EeV}={10}^{18}\mathrm{eV}$). We find that strong constraints on the source evolution can be obtained by combining measurements of the cosmic ray proton fraction above 30 EeV with measurement of the neutrino flux at 1 EeV, if neutrinos are predominantly of cosmogenic origin. In the case that interactions in the source environment produce a significant astrophysical neutrino flux, constraints on the source evolution may require measurement of the observed proton fraction, as well as, the neutrino flux at multiple energies, such as 1 EeV and 10 EeV. Finally, we show that fits to current UHECR data favor models which result in a $>30\mathrm{EeV}$ proton fraction and 1 EeV neutrino flux that could realistically be discovered by the next generation of experiments.

We consider the effects of a noisy magnetic field background over the fermion propagator in QED as an approximation to the spatial inhomogeneities that would naturally arise in certain physical scenarios, such as heavy-ion collisions or the quark-gluon plasma in the early stages of the evolution of the Universe. We considered a classical, finite, and uniform average magnetic field background $⟨\mathbf{B}(\mathbf{x})⟩=\mathbf{B}$, subject to white-noise spatial fluctuations with autocorrelation of magnitude ${\mathrm{\Delta }}_B$. By means of the Schwinger representation of the propagator in the average magnetic field as a reference system, we used the replica formalism to study the effects of the magnetic noise in the form of renormalized quasiparticle parameters, leading to an effective charge and an effective refraction index that depend not only on the energy scale, as usual, but also on the magnitude of the noise ${\mathrm{\Delta }}_B$ and the average field $\mathbf{B}$.

The advent of laser-driven high-intensity $\gamma$-photon beams has opened up new opportunities for designing advanced photon-photon colliders. Such colliders have the potential to produce a large yield of linear Breit-Wheeler (LBW) pairs in a single shot, which offers a unique platform for studying the polarized LBW process. In our recent work [Q. Zhao et al., Signatures of linear Breit-Wheeler pair production in polarized $\gamma \gamma$ collisions, Phys. Rev. D 105, L071902 (2022)], we investigated the polarization characteristics of LBW pair production in circularly-polarized ($CP$) $\gamma$-photon collisions. To fully clarify the polarization effects involving both $CP$ and linearly-polarized $\gamma$-photons, here we further investigate the LBW process using the polarized cross section with explicit azimuthal-angle dependence due to the base rotation of photon-polarization vectors. We accomplished this by defining a new spin basis for positrons and electrons, which enables us to decouple the transverse and longitudinal spin components of $e^{\pm }$. By means of analytical calculations and Monte Carlo simulations, we find that the linear polarization of photon can induce the highly angle-dependent pair yield and polarization distributions. The comprehensive knowledge of the polarized LBW process will also open up avenues for investigating the higher-order photon-photon scattering, the laser-driven quantum electrodynamic plasmas and the high-energy astrophysics.

Traditional dark matter models, e.g., weakly interacting massive particles (WIMPs), assume dark matter (DM) is weakly coupled to the standard model so that elastic scattering between dark matter and baryons can be described perturbatively by the Born approximation; most direct detection experiments are analyzed according to that assumption. We show that when the fundamental DM-baryon interaction is attractive, dark matter-nucleus scattering is nonperturbative in much of the relevant parameter range. The cross section exhibits rich resonant behavior with a highly nontrivial dependence on atomic mass; furthermore, the extended rather than pointlike nature of nuclei significantly impacts the cross sections and must therefore be properly taken into account. The repulsive case also shows significant departures from perturbative predictions and also requires full numerical calculation. These nonperturbative effects change the boundaries of exclusion regions from existing direct detection, astrophysical and CMB constraints. Near a resonance value of the parameters the typical velocity-independent Yukawa behavior, $\sigma \sim v^0$, does not apply. We take the nontrivial velocity dependence into account in our analysis, however it turns out that this more accurate treatment has little impact on limits given current constraints. Correctly treating the extended size of the nucleus and doing an exact integration of the Schrödinger equation does have a major impact relative to past analyses based on the Born approximation and naive form factors, so those improvements are essential for interpreting observational constraints. We report the corrected exclusion regions superseding previous limits from XQC, CRESST Surface Run, CMB power spectrum and extensions with Lyman-$\alpha$ and Milky Way satellites, and Milky Way gas clouds. Some limits become weaker, by an order of magnitude or more, than previous bounds in the literature which were based on perturbation theory and pointlike sources, while others become stronger. Gaps which open by correct treatment of some particular constraint can sometimes be closed using a different constraint. We also discuss the dependence on mediator mass and give approximate expressions for the velocity dependence near a resonance. Sexaquark ($uuddss$) DM with mass around 2 GeV, which exchanges QCD mesons with baryons, remains unconstrained for most of the parameter space of interest. A statement in the literature that a DM-nucleus cross section larger than ${10}^{-25}{\mathrm{cm}}^2$ implies dark matter is composite, is corrected.

Motivated by the collisionless cold dark matter small scale structure problem, we propose an asymmetric dark matter model with the dark sector charged under a dark $U(1{)}^{\prime }$. The mediator between dark matter particles is the dark gauge boson, which obtains its mass through the spontaneous breaking of $U(1{)}^{\prime }$. This model easily avoids the strong limits from cosmic microwave background (CMB) observation, and has a large parameter space to be consistent with small scale structure data. We focus on a special scenario where portals between the dark sector and visible sector are too weak to be detected by traditional methods. We find that this scenario can increase the effective number of neutrinos ($N_{\mathrm{eff}}$). In addition, the spontaneous $U(1{)}^{\prime }$ symmetry breaking process can generate stochastic gravitational waves with peak frequency around ${10}^{-6}–{10}^{-7}\mathrm{Hz}$.

We study the one-loop corrections to $W^{+}{W}^{-}$ elastic scattering within the framework of effective theories. Rescattering via intermediate electroweak would-be-Goldstone bosons dominate at high energies, as the corresponding loop diagrams with these intermediate bosons scale like $\mathcal{O}(s^2/v^4)$ in the chiral effective counting. In the present article, we focus our attention on the usually neglected fermion-loop corrections which scale like $\mathcal{O}(M_{\mathrm{fer}}^{2}s/v^4)$ in the Higgs effective field theory (HEFT). Although this dependency is formally suppressed for $s\to \infty$ with respect to the ones from boson loops, the large top mass can lead to a numerical competition between fermion and boson loops at intermediate energies of the order of a few TeV. The central goal of the present study is to assess the importance of these fermion loops. For this, since the fermion contribution scales with the mass of the fermions, we have calculated the imaginary part induced by loops of the heaviest fermions, top and bottom quarks, in $W^{+}{W}^{-}\to W^{+}{W}^{-}$ elastic scattering and compared them with the loop contributions from purely bosonic loops, as a large imaginary part would be a clear indicator of large fermion-loop effects. We have examined the dependence of both amplitudes on the effective couplings, allowing an $\mathcal{O}(10\%)$ deviation from the Standard Model. In some cases, boson loops dominate over top and bottom corrections, as expected. However, we find that there are regions in the space of effective parameters that yield a significant—and even dominant—imaginary contribution from fermion loops. In addition to our conclusions for the general HEFT, we also provide analyses particularized to some benchmark points in the $SO(5)/SO(4)$ minimal composite Higgs model.

Cosmic-ray muons that enter the Super-Kamiokande detector cause hadronic showers due to spallation in water, producing neutrons and radioactive isotopes. These are a major background source for studies of MeV-scale neutrinos and searches for rare events. In 2020, gadolinium was introduced into the ultra-pure water in the Super-Kamiokande detector to improve the detection efficiency of neutrons. In this study, the cosmogenic neutron yield was measured using data acquired during the period after the gadolinium loading. The yield was found to be $(2.76\pm 0.02(\mathrm{stat})\pm 0.19(\mathrm{syst}))\times {10}^{-4}{\mathrm{\mu }}^{-1}{\mathrm{g}}^{-1}{\mathrm{cm}}^2$ at an average muon energy 259 GeV at the Super-Kamiokande detector.

A precision measurement of the matrix elements for $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ and $\eta \to {\pi }^0{\pi }^0{\pi }^0$ decays is performed using a sample of $(10087\pm 44)\times {10}^{6}J/\psi$ decays collected with the BESIII detector. The decay $J/\psi \to \gamma \eta$ is used to select clean samples of $631,686\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ decays and $272,322\eta \to {\pi }^0{\pi }^0{\pi }^0$ decays. The matrix elements for both channels are in reasonable agreement with previous measurements. The nonzero $g{X}^{2}Y$ term for the decay mode $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ is confirmed, as reported by the KLOE Collaboration, while the other higher-order terms are found to be insignificant. Dalitz plot asymmetries in the $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ decay are also explored and are found to be consistent with charge conjugation invariance. In addition, a cusp effect is investigated in the $\eta \to {\pi }^0{\pi }^0{\pi }^0$ decay, and no obvious structure around the ${\pi }^{+}{\pi }^{-}$ mass threshold is observed.

The axion-nucleon coupling enables the production of axions through the decay of excited ${}^{57}\mathrm{Fe}$ nuclei, and axions produced in the Sun through this process are often a target of helioscope searches. We show for the first time that hot, highly magnetic white dwarfs such as ZTF $\mathrm{J}1901+1458$ are a viable target to search for the x-ray signature of axions that were produced by the ${}^{57}\mathrm{Fe}$ transition in the core and then converted to photons in the magnetosphere. We calculate that a 100 ks observation of ZTF $\mathrm{J}1901+1458$ with NuSTAR would constrain the coupling of axions to nucleons and photons at a level below the bounds of both current and future planned helioscopes.

We propose an alternative scenario for the axion misalignment mechanism based on the nontrivial interplay between the axion and a light dilaton in the early universe. Dark matter abundance is still sourced by the initial misalignment of the axion field, whose motion along the potential kicks the dilaton field away from its minimum, and dilaton starts to oscillate later with a delayed onset time for oscillation and a relatively large misalignment value due to the kick; eventually the dilaton dominates over the axion in their energy densities, and the dilaton is identified as dark matter. The kick effect due to axion motion is the most significant if the initial field value of dilaton is near its minimum; therefore, we call this scenario the axion “free-kick” misalignment mechanism, where the axion plays the role similar to a football player. Dark matter abundance can be obtained with a lower axion decay constant compared to the conventional misalignment mechanism.

We propose an observable $q_{*}$ sensitive to transverse momentum dependence (TMD) in $eN\to ehX$, with $q_{*}/E_N$ defined purely by lab-frame angles. In 3D measurements of confinement and hadronization this resolves the crippling issue of accurately reconstructing small transverse momentum $P_{hT}$. We prove factorization for $\mathrm{d}{\sigma }_h/\mathrm{d}{q}_{*}$ for $q_{*}\ll Q$ with standard TMD functions, enabling $q_{*}$ to substitute for $P_{hT}$. A double-angle reconstruction method is given which is exact to all orders in QCD for $q_{*}\ll Q$. $q_{*}$ enables an order-of-magnitude improvement in the expected experimental resolution at the EIC.

We discuss two different approaches to synthesize holographic nonrelativistic fluid from its relativistic counterpart. In the first approach we obtain the nonrelativistic fluid by light-cone reduction of a relativistic conformal fluid. In the second approach we consider the bulk dual of the relativistic fluid, uplift the solution to 10 dimensions and perform TsT transformations on the bulk solution to change the asymptotic structure. Reducing the TsT transformed geometry over $S^5$ we find an effective 5 dimensional locally boosted solution. We then use the bulk-boundary dictionary to compute the nonrelativistic constitutive relations. We show that the nonrelativistic fluids obtained by these two methods are equivalent up to second order in derivative expansion. Our results also provide explicit expressions for different constitutive relations and transports of holographic $U(1)$ charged nonrelativistic fluids (both parity odd and even) up to second order in derivative expansion.

In this paper, we introduce new sets of boundary conditions for higher-spin gravity in ${\mathrm{AdS}}_3$ where the boundary dynamics of spin-2 and other higher-spin fields are governed by the interacting collective field theory Hamiltonian of Avan and Jevicki. We show that the time evolution of spin-2 and higher-spin fields can be captured by the classical dynamics of folded Fermi surfaces in the similar spirit of Lin, Lunin, and Maldacena. We also construct infinite sequences of conserved charges showing the integrable structure of higher-spin gravity (for spin-3) under the boundary conditions we considered. Further, we observe that there are two possible sequences of conserved charges depending on whether the underlying boundary fermions are nonrelativistic or relativistic.

We consider a quantum real massive scalar field in the de Sitter–Schwarzschild spacetime background. To have an analytic headway we study in detail the two-dimensional case, assuming that the situation in four dimensions will not be much different conceptually. It is assumed that the quantum field is in a thermal state, i.e., described by the Planckian distribution for the exact modes in the geometry under consideration. We calculate approximately the expectation value of the stress-energy tensor near the cosmological and black hole horizons. It is shown that for a generic temperature backreaction from quantum fields, the geometry cannot be neglected. Thus, de Sitter–Schwarzschild spacetime geometry inevitably is strongly modified by the quantum fluctuations of the matter fields.

We extract the Hubble law by the frequency-shift considerations of test particles revolving the Kerr black hole in asymptotically de Sitter spacetime. To this end, we take into account massive geodesic particles circularly orbiting the Kerr-de Sitter black holes that emit redshifted photons towards a distant observer which is moving away from the emitter-black hole system. By considering this configuration, we obtain an expression for redshift in terms of the spacetime parameters, such as mass, angular momentum, and the cosmological constant. Then, we find the frequency shift of photons versus the Hubble constant with the help of some physically motivated approximations. Finally, some exact formulas for the Schwarzschild black hole mass and the Hubble constant in terms of the observational redshift of massive bodies circularly orbiting this black hole are extracted. Our results suggest a new independent general relativistic approach to obtaining the late-time Hubble constant in terms of observable quantities.

The detection of gravitational waves from the coalescences of binary compact stars by current interferometry experiments has opened up a new era of gravitational-wave astrophysics and cosmology. The search for a stochastic gravitational-wave background is underway by correlating signals from a pair of detectors in the detector network formed by the LIGO, Virgo, and KAGRA. In a previous work, we have developed a method based on spherical harmonic expansion to calculate the overlap reduction functions of the LIGO-Virgo-KAGRA network for a polarized stochastic gravitational-wave background. In this work, we will apply the method to calculate the overlap reduction functions of third-generation detectors such as a ground-based network linking the Einstein Telescope, the Cosmic Explorer, and the LISA-Taiji joint space mission.