We recently showed that if a massive (or charged) body is put in a quantum spatial superposition, the mere presence of a black hole in its vicinity will eventually decohere the superposition. In this paper we show that, more generally, decoherence of stationary superpositions will occur in any spacetime with a Killing horizon. This occurs because, in effect, the long-range field of the body is registered on the Killing horizon which, we show, necessitates a flux of “soft horizon gravitons/photons” through the horizon. The Killing horizon thereby harvests “which path” information of quantum superpositions and will decohere any quantum superposition in a finite time. It is particularly instructive to analyze the case of a uniformly accelerating body in a quantum superposition in flat spacetime. As we show, from the Rindler perspective the superposition is decohered by “soft gravitons/photons” that propagate through the Rindler horizon with negligible (Rindler) energy. We show that this decoherence effect is distinct from—and larger than—the decoherence resulting from the presence of Unruh radiation. We further show that from the inertial perspective, the decoherence is due to the radiation of high frequency (inertial) gravitons/photons to null infinity. (The notion of gravitons/photons that propagate through the Rindler horizon is the same notion as that of gravitons/photons that propagate to null infinity.) We also analyze the decoherence of a spatial superposition due to the presence of a cosmological horizon in de Sitter spacetime. We provide estimates of the decoherence time for such quantum superpositions in both the Rindler and cosmological cases. Although we explicitly treat the case of spacetime dimension $d=4$, our analysis applies to any dimension $d\ge 4$.

We use gravitational waves (GWs) from binary black holes (BBHs) and neutron stars inspiraling into intermediate-mass black holes to evaluate how accurately the future space-based GW detectors such as LISA, Taiji, and TianQin and their combined networks can determine source parameters and constrain alternative theories of gravity. We find that, compared with single detector, the detector network can greatly improve the estimation errors of source parameters, especially the sky localization, but the improvement of the constraint on the graviton mass $m_g$ and the Brans-Dicke coupling constant ${\omega }_{\mathrm{BD}}$ is small. We also discuss possible scalar modes existed in alternative theories of gravity, and we find the inclusion of the scalar mode has little effect on the constraints on source parameters, $m_g$, and ${\omega }_{\mathrm{BD}}$ and the parametrized amplitude $A_B$ of scalar modes are small. For the constraint on the graviton mass, we consider both the effects in the GW phase and the transfer function due to the mass of graviton. With the network of LISA, Taiji, and TianQin, we get the lower bound on the graviton Compton wavelength ${\lambda }_g\gtrsim 1.24\times {10}^{20}\mathrm{m}$ for BBHs with masses $({10}^6+{10}^7)M_{\odot }$, and $A_B<5.7\times {10}^{-4}$ for BBHs with masses $(1+2)\times {10}^5{M}_{\odot }$; ${\omega }_{\mathrm{BD}}>6.11\times {10}^6$ for neutron star–black hole binary with masses $(1.4+400)M_{\odot }$.

We compare numerical self-force results and analytical fourth-order post-Minkowskian (PM) calculations for hyperbolic-type scattering of a pointlike particle carrying a scalar charge $Q$ off a Schwarzschild black hole, showing a remarkably good agreement. Specifically, we numerically compute the scattering angle including the full $\mathcal{O}(Q^2)$ scalar-field self-force term (but ignoring the gravitational self-force), and we compare with analytical expressions obtained in a PM framework using scattering-amplitude methods. This example provides a nontrivial, high-precision test of both calculation methods and illustrates the complementarity of the two approaches in the context of the program to provide high-precision models of gravitational two-body dynamics. Our PM calculation is carried out through 4PM order, i.e., including all terms through $\mathcal{O}(Q^2{G}^3)$. At the fourth post-Minkowskian order the point-particle description involves two a priori undetermined coefficients, due to contributions from tidal effects in the model under consideration. These coefficients are chosen to align the post-Minkowskian results with the self-force ones.

Black-hole binary spin precession admits equilibrium solutions corresponding to systems with (anti)aligned spins. Among these, binaries in the up-down configuration, where the spin of the heavier (lighter) black hole is co(counter)aligned with the orbital angular momentum, might be unstable to small perturbations of the spin directions. The occurrence of the up-down instability leads to gravitational-wave sources that formed with aligned spins but are detected with precessing spins. We present a Bayesian procedure based on the Savage-Dickey density ratio to test the up-down origin of gravitational-wave events. This is applied to both simulated signals, which indicate that achieving strong evidence is within the reach of current experiments, and the LIGO/Virgo events released to date, which indicate that current data are not informative enough.

We study scalar perturbations of topological solitons, smooth horizonless solutions in five-dimensional Einstein-Maxwell theory, that correspond to coherent states of gravity via the dynamics of extra compact dimensions. First, we compute scalar quasinormal modes for topological stars that have a single unstable photon sphere, and we show that the spectrum is very similar to that of a black hole with the same photon sphere. Next, we study topological stars that have both a stable inner photon sphere and an unstable one. The first few quasinormal modes are localized around the inner photon sphere. The spectrum also contains “black-hole-like modes” localized at the unstable outer photon sphere. The frequencies of these modes are similar to those of a black hole, but their imaginary part is smaller due to a cavity effect associated with the inner photon sphere. The longer damping produced by this trapping effect may have implications for black hole spectroscopy.

Galactic binaries, and notably double white dwarfs systems, will be a prominent source for the future LISA and Einstein Telescope detectors. Contrary to the black holes observed by the current LIGO-Virgo-KAGRA network, such objects bear intense magnetic fields that are naturally expected to leave some imprints on the gravitational wave emission. The purpose of this work is thus to study those imprints within the post-Newtonian (PN) framework, particularly adapted to double white dwarfs systems. To this end, we construct an effective action that takes into account the whole electromagnetic structure of a star, and then specify it to dipolar order. With this action at hand, we compute the acceleration and Noetherian quantities for generic electric and magnetic dipoles, at a relative 2PN order. Finally, focusing on physically relevant systems, we show that the magnetic effects on the orbital frequency, energy, and angular momentum is significant, confirming the conclusions of previous works.

We generalize previously derived analytic results for the one-loop power spectrum (PS) in scale-free models (with linear PS $P(k)\propto k^n$) to a broader class of such models in which part of the matter-like component driving the Einstein de Sitter expansion does not cluster. These models can be conveniently parametrized by $\alpha$, the constant logarithmic linear growth rate of fluctuations (with $\alpha =1$ in the usual case). $\text{For}-3<n<-1$, where the one-loop PS is both infrared and ultraviolet convergent and thus explicitly self-similar, it is characterized conveniently by a single numerical coefficient $c(n,\alpha )$. We compare the analytical predictions for $c(n=-2,\alpha )$ with results from a suite of $N$-body simulations with $\alpha \in [0.25,1]$ performed with an appropriately modified version of the gadget code. Although the simulations are of small (${256}^3$) boxes, the constraint of self-similarity allows the identification of the converged PS at a level of accuracy sufficient to test the analytical predictions for the $\alpha$ dependence of the evolved PS. Good agreement for the predicted dependence on $\alpha$ of the PS is found. To treat the UV sensitivity of results which grows as one approaches $n=-1$, we derive exact results incorporating a regularization $k_c$ and obtain expressions for $c(n,\alpha ,k_c/k)$. Assuming that this regularization is compatible with self-similarity allows us to infer a predicted functional form of the PS equivalent to that derived in effective field theory (EFT). The coefficient of the leading EFT correction at one loop has a strong dependence on $\alpha$, with a change in sign at $\alpha \approx 0.16$, providing a potentially stringent test of EFT.

If the inflaton field is coupled to the hypercharge Chern-Simons density $F\tilde{F}$, an explosive production of helical gauge fields when inflation ends can trigger baryogenesis at the electroweak phase transition. Besides, Higgs inflation identifies the inflaton with the Higgs field $\mathcal{H}$, thus relating cosmological observables to properties of electroweak physics. In this paper we merge both approaches; the helical gauge fields are produced at the end of Higgs inflation from the coupling $|\mathcal{H}{|}^{2}F\tilde{F}$. In the metric formulation of gravity we found a window in the parameter space for electroweak baryogenesis consistent with all experimental observations. Conversely, for the Palatini formalism the non-Gaussianity bounds strongly constrain the helicity produced at the end of inflation, forbidding an efficient baryogenesis.

Direct detection for sub-GeV dark matter is developing rapidly, with many novel experimental ideas and theoretical methods emerging. In this work, we extend the dielectric formalism for dark matter scattering to incorporate anisotropic material responses, enabling directionally sensitive experiments with a broad class of target materials. Using a simple model of an anisotropic electron gas, we demonstrate the importance of many-body effects such as the plasmon and show that, even when the dark matter kinetic energies are much smaller than the plasmon energy, the tail of an anisotropic plasmon can still produce a sizable daily modulation. We highlight the relevant experimental techniques required to establish the target response as well as the challenges in extracting a response function which is truly free of modeling uncertainties.

It is generically believed that the two-body scattering is suppressed by higher-order weak couplings with respect to the two-body decay. We show that this does not always hold when a heavy particle is produced by a forbidden decay in a thermal plasma, where the scattering shares the same order of couplings with the decay. We find that there is a simple and close relation between the forbidden decay and the same-order scattering. To illustrate this point, we consider the freeze-in production of heavy dark matter via a light scalar mediator. We point out that when the Boltzmann (quantum) statistics is used, the forbidden decay can contribute to the dark matter relic density at 5%–24% (10%–39%) with a weak thermal coupling, while the contribution from the scattering channel can be several orders of magnitude larger than from the forbidden decay if the thermal coupling is much smaller. Such a relative effect between the scattering and the forbidden decay could also exist in other plasma-induced processes, such as the purely thermal generation of the right-handed neutrino dark matter, or of the lepton asymmetry in leptogenesis.

We revisit a cosmological scenario based on the classically conformal $U(1{)}_{B-L}$ extension of the Standard Model. Our focus is on the mechanism of reheating after inflation and the constraints on the model parameters. In this scenario, the inflationary dynamics is driven by the $U(1{)}_{B-L}$ Higgs field that is nonminimally coupled to gravity and breaks the $U(1{)}_{B-L}$ symmetry spontaneously as it acquires a vacuum expectation value through the Coleman-Weinberg mechanism. It is found that the reheating process proceeds stepwise, and as the decay channels of the $U(1{)}_{B-L}$ Higgs field are known, the reheating temperature is evaluated. The relation between the $e$-folding number of inflation and the reheating temperature provides a strong consistency condition on the model parameters, and we find that the recent cosmological data give an upper bound on the $U(1{)}_{B-L}$ breaking scale $v_{BL}\lesssim {10}^{12}\mathrm{GeV}$. The lower bound is $v_{BL}\gtrsim {10}^6\mathrm{GeV}$, obtained as the condition for successful reheating in this model. The prediction for the cosmic microwave background (CMB) spectrum of this model fits extremely well with today’s cosmological data. The model can be tested and is falsifiable by near future CMB observations, including the LiteBIRD and CMB-S4.

We calculate the mass spectra of ${\mathrm{\Lambda }}_c$, ${\mathrm{\Xi }}_c$, ${\mathrm{\Sigma }}_c$, ${\mathrm{\Xi }}_c^{\prime }$, and ${\mathrm{\Omega }}_c$ baryons in the framework of a quark-diquark configuration using the relativistic flux tube model. The spin-dependent interactions are included in the j-j coupling scheme to find the complete mass spectra. We satisfactorily describe the known singly charmed baryons in a quark-diquark configuration. The possible spin-parity $J^P$ quantum numbers are assigned to several experimentally observed states. Furthermore, some useful mass predictions are given for more excited states that are reasonably consistent with other model predictions for lower excited states. From the obtained results, the Regge trajectories for these singly charmed baryons are constructed in the ($J$, $M^2$) plane, and the properties like linearity, parallelism, and equidistance are verified. Also, these predictions should be tested in future experiments.

The calculations based on the next-to-leading logarithm (NLL) approximation for the Balitsky-Fadin-Kuraev-Lipatov (BKFL) evolution are presented for the Mueller-Navelet (MN) dijet production cross section, as well as for their ratios at different collision energies. The MN dijet denotes the jet pair consists of jets, which were selected with $p_{\perp }>p_{\perp \min }$ and with maximal rapidity separation in the event. The NLL BFKL predictions for the MN cross sections are given for the $pp$ collisions at $\sqrt{s}=2.76$, 8, and 13 TeV, for $p_{\perp \min }=20$ and 35 GeV. The results are in agreement with the measurement by the Compact Muon Solenoid (CMS) experiment in $pp$ collisions at $\sqrt{s}=2.76\mathrm{TeV}$ and $p_{\perp \min }=35\mathrm{GeV}$ within the theoretical and experimental uncertainties. The predictions of the NLL BFKL calculation of ratios of the MN cross sections at different collision energies and $p_{\perp \min }$ are also presented.

The process of electron-positron pair creation and oscillation in a uniform electric field is studied, taking into account the Pauli exclusion principle. Generally, we find that pair creation is suppressed; hence, coherent oscillations occur on longer timescales. Considering pair creation in already existing electron-positron plasma, we find that the dynamics depends on pair distribution function. We considered Fermi-Dirac distribution of pairs and found that for small temperatures pair creation is suppressed, while for small chemical potentials it increases: heating leads to enhancement of pair creation.

Using $(1.0087\pm 0.0044)\times {10}^{10}J/\psi$ events collected by the BESIII detector at the BEPCII collider, we report the first search for the baryon and lepton number violating decays ${\mathrm{\Xi }}^0\to K^{-}{e}^{+}$ with $\mathrm{\Delta }(B-L)=0$ and ${\mathrm{\Xi }}^0\to K^{+}{e}^{-}$ with $|\mathrm{\Delta }(B-L)|=2$, where $B$ ($L$) is the baryon (lepton) number. While no signal is observed, the upper limits on the branching fractions of these two decays are set to $\mathcal{B}({\mathrm{\Xi }}^0\to K^{-}{e}^{+})<3.6\times {10}^{-6}$ and $\mathcal{B}({\mathrm{\Xi }}^0\to K^{+}{e}^{-})<1.9\times {10}^{-6}$ at the 90% confidence level, respectively. These results offer a direct probe of baryon number violating interactions involving a strange quark.

Isolated ideal neutron stars (NS) of age $>{10}^9\mathrm{yr}$ exhaust thermal and rotational energies and cool down to temperatures below $\mathcal{O}(100)\mathrm{K}$. Accretion of particle dark matter (DM) by such NS can heat them up through kinetic and annihilation processes. This increases the NS surface temperature to a maximum of $\sim 2550\mathrm{K}$ in the best case scenario. The maximum accretion rate depends on the DM ambient density and velocity dispersion, and on the NS equation of state and their velocity distributions. Upon scanning over these variables, we find that the effective surface temperature varies at most by $\sim 40\%$. Black-body spectrum of such warm NS peak at near infrared wavelengths with magnitudes in the range potentially detectable by the James Webb Space Telescope (JWST). Using the JWST exposure time calculator, we demonstrate that NS with surface temperatures $\gtrsim 2400\mathrm{K}$, located at a distance of 10 pc can be detected through the F150W2 (F322W2) filters of the NIRCAM instrument at $\mathrm{SNR}\gtrsim 10$ (5) within 24 hours of exposure time. Independently of DM, an observation of NS with surface temperatures $\gtrsim 2500\mathrm{K}$ will be a formative step toward testing the minimal cooling paradigm during late evolutionary stages.

Traditionally, gravitational waves are detected with techniques such as matched filtering or unmodeled searches based on wavelets. However, in the case of generic black hole binaries with nonaligned spins, if one wants to explore the whole parameter space, matched filtering can become impractical, which sets severe restrictions on the sensitivity and computational efficiency of gravitational-wave searches. Here, we use a novel combination of machine-learning algorithms and arrive at sensitive distances that surpass traditional techniques in a specific setting. Moreover, the computational cost is only a small fraction of the computational cost of matched filtering. The main ingredients are a 54-layer deep residual network (ResNet), a deep adaptive input normalization (DAIN), a dynamic dataset augmentation, and curriculum learning, based on an empirical relation for the signal-to-noise ratio. We compare the algorithm’s sensitivity with two traditional algorithms on a dataset consisting of a large number of injected waveforms of nonaligned binary black hole mergers in real LIGO O3a noise samples. Our machine-learning algorithm can be used in upcoming rapid online searches of gravitational-wave events in a sizeable portion of the astrophysically interesting parameter space. We make our code, AResGW, and detailed results publicly available at https://github.com/vivinousi/gw-detection-deep-learning.

Starting from a generalized Kaluza-Klein action including arbitrary Horndeski potentials, we establish integrability and compatibility conditions that solve the generic field equations for spherical symmetry. The resulting theories can be identified as general Horndeski theories having no apparent symmetries in four dimensions or as effective string theory actions with an IR logarithmic running for the dilaton, higher-order corrections and generalized Liouville-type potentials. For such actions, we then find black holes with secondary hair parametrized by two coupling constants essentially characterizing the theories at hand. One is related to an action which is conformally coupled in five dimensions, while the second is related to a Kaluza-Klein reduction of Lovelock theory. We show that the full action can also be interpreted as a sum of conformally coupled actions in differing dimensions. Known solutions are mapped within the general chart of the found theories, and novel general black holes are discussed, focusing on their important properties and some of their observational constraints.

We develop approximate “analytic-kludge” waveforms to describe the inspiral of a stellar-mass compact object into a supermassive compact object in an extreme mass ratio inspiral (EMRI) scenario. The deformability of the supermassive compact object is characterized by a dimensionless quantity called the tidal Love number (TLN). Our analysis shows that, up to the leading order of the mass ratio, the conservative dynamics of the EMRI are not affected by tidal interaction, and the tidal effect is only present in the induced quadrupole moment. We calculate the energy and angular momentum fluxes and obtain leading order corrections to the orbital evolution equations. By comparing the waveforms with and without tidal interaction, we demonstrate that even a small TLN can produce significant differences in the waveforms, which can be detected by space-borne detector LISA. Finally, using the Fisher information matrix method, we perform parameter estimation for the TLN and find that the precision can reach the level of ${10}^{-4}$ in suitable scenarios.

We study gravitational wave microlensing by primordial black holes (PBHs), accounting for the effect of a particle dark matter minihalo surrounding them. Such minihaloes are expected when PBHs make up only a fraction of all dark matter. We find that current LIGO-Virgo detections disfavor dark matter in the form of PBHs heavier than $100M_{\odot }$ at $1.4\sigma$. The next generation observatories can potentially probe PBHs as light as $0.01M_{\odot }$ and down to $2\times {10}^{-4}$ fraction of all dark matter. We also show that these detectors can distinguish between dressed and naked PBHs, providing a novel way to study the distribution of particle dark matter around black holes and potentially shed light on the origins of black holes.