Using a data sample of $(1310.6\pm 7.0)\times {10}^{6}J/\psi$ events taken with the BESIII detector at the center-of-mass energy of 3.097 GeV, we search for the first time for the lepton number violating decay ${\mathrm{\Sigma }}^{-}\to p{e}^{-}{e}^{-}$ and the rare inclusive decay ${\mathrm{\Sigma }}^{-}\to {\mathrm{\Sigma }}^{+}X$, where $X$ denotes any possible particle combination. The ${\mathrm{\Sigma }}^{-}$ candidates are tagged in $J/\psi \to \overline{\mathrm{\Sigma }}(1385{)}^{+}{\mathrm{\Sigma }}^{-}$ decays. No signal candidates are found, and the upper limits on the branching fractions at the 90% confidence level are determined to be $\mathcal{B}({\mathrm{\Sigma }}^{-}\to p{e}^{-}{e}^{-})<6.7\times {10}^{-5}$ and $\mathcal{B}({\mathrm{\Sigma }}^{-}\to {\mathrm{\Sigma }}^{+}X)<1.2\times {10}^{-4}$.

In this paper, the thermodynamic properties of a thin black ring in AdS space-time is explored when the size of the ring is comparable to quantum scales. The angular momentum to mass ratio of this system has an upper limit, which is the cosmological radius of the black ring. It is found that the small black ring will be thermodynamically stable due to the effects introduced by thermal fluctuations. However, we find that the black ring is less stable than thermal AdS. Thermodynamic analysis indicates that there is no critical point, but there is Hawking-Page transition to radiation, which is confirmed by the Gibbs free energy analysis.

Robinson-Trautman solutions with nonlinear electrodynamics are investigated for both $\mathbb{L}(F)$ and $\mathbb{L}(F,G)$ Lagrangians, and the presence of electric and magnetic charges as well as electromagnetic radiation is assumed. Particular interest is devoted to models representing regular black holes for spherically symmetric situations. The results show the clear uniqueness of Maxwell electrodynamics with respect to compatibility with the Robinson-Trautman class. Additionally, regular black hole models are clearly not suited to this class, while the famous Born-Infeld model illustrates an important distinction between $\mathbb{L}(F)$ and $\mathbb{L}(F,G)$ as regards the electric field we obtain when the magnetic field is nontrivial.

In this paper we consider the massive scalar perturbation on the top of a small spinning-like black hole in context of Einstein-bumblebee modified gravity in order to probe the role of spontaneous Lorentz symmetry breaking on the superradiance scattering and corresponding instability. We show that at the low-frequency limit of the scalar wave the superradiance scattering will be enhanced with the Lorentz-violating parameter $\alpha <0$ and will be weakened with $\alpha >0$. Moreover, by addressing the black hole bomb issue, we extract an improved bound in the instability regime indicating that $\alpha <0$ increases the parameter space of the scalar field instability, while $\alpha >0$ decreases it.

We show that the Plebański-Demiański spacetime persists as a solution of general relativity when the theory is supplemented with both, a conformally coupled scalar theory and with quadratic curvature corrections. The quadratic terms are of two types and are given by quadratic combinations of the Riemann tensor as well as a higher curvature interaction constructed with a scalar field which is conformally coupled to quadratic terms in the curvature. The later is built in terms of a four-rank tensor ${S_{\mu \nu }}^{\lambda \rho }$ that depends on the Riemann tensor and the scalar field, and that transforms covariantly under local Weyl rescalings. Due to the generality of the Plebański-Demiański family, several new hairy black hole solutions are obtained in this higher curvature model. We pay particular attention to the C-metric spacetime and the stationary Taub-NUT metric, which in the hyperbolic case can be analytically extended leading to healthy, asymptotically AdS, wormhole configurations. Finally, we present a new general model for higher derivative, conformally coupled scalars, depending on an arbitrary function and that we have dubbed conformal $K$ essence. We also construct spherically symmetric hairy black holes for these general models.

We study static spherically symmetric solutions to the vacuum field equations of quadratic gravity in the presence of a cosmological constant $\mathrm{\Lambda }$. Motivated by the trace no-hair theorem, we assume the Ricci scalar to be constant throughout a spacetime. Furthermore, we employ the conformal-to-Kundt metric ansatz that is valid for all static spherically symmetric spacetimes and leads to a considerable simplification of the field equations. We arrive at a set of two ordinary differential equations and study its solutions using the Frobenius-like approach of (infinite) power series expansions. While the indicial equations considerably restrict the set of possible leading powers, careful analysis of higher-order terms is necessary to establish the existence of the corresponding classes of solutions. We thus obtain various non-Einstein generalizations of the Schwarzschild, (anti-)de Sitter [or (A)dS for short], Nariai, and Plebański-Hacyan spacetimes. Interestingly, some classes of solutions allow for an arbitrary value of $\mathrm{\Lambda }$, while other classes admit only discrete values of $\mathrm{\Lambda }$. For most of these classes, we give recurrent formulas for all series coefficients. We determine which classes contain the Schwarzschild-(A)dS black hole as a special case and briefly discuss the physical interpretation of the spacetimes. In the discussion of physical properties, we naturally focus on the generalization of the Schwarzschild-(A)dS black hole, namely the Schwarzschild-Bach-(A)dS black hole, which possesses one additional Bach parameter. We also study its basic thermodynamical properties and observable effects on test particles caused by the presence of the Bach tensor. This work is a considerable extension of our Letter [Phys. Rev. Lett. 121, 231104 (2018)].

Extreme-mass-ratio inspirals, in which a stellar-mass compact object spirals into a supermassive black hole in a galactic core, are expected to be key sources for LISA. Modeling these systems with sufficient accuracy for LISA science requires going to second (or postadiabatic) order in gravitational self-force theory. Here we present a practical two-timescale framework for achieving this and generating postadiabatic waveforms. The framework comprises a set of frequency-domain field equations that apply on the fast, orbital timescale, together with a set of ordinary differential equations that determine the evolution on the slow, inspiral timescale. Our analysis is restricted to the special case of quasicircular orbits around a Schwarzschild black hole, but its general structure carries over to the realistic case of generic (inclined and eccentric) orbits in Kerr spacetime. In our restricted context, we also develop a tool that will be useful in all cases: a formulation of the frequency-domain field equations using hyperboloidal slicing, which significantly improves the behavior of the sources near the boundaries. We give special attention to the slow evolution of the central black hole, examining its impact on both the two-timescale evolution and the earlier self-consistent evolution scheme.

We study the interferometric observation of intensity and polarization anisotropies of a stochastic gravitational wave background. We show that the observed correlated data is defined in the group manifold of the three-dimensional rotation. Explicit correlation between two detectors in the interferometry experiments such as LIGO-Virgo and KAGRA is constructed in terms of the Wigner-$D$ functions. Our results may provide a tool for constructing data pipelines to estimate the power spectra of the stochastic gravitational wave background anisotropies.

We study the quantum circuit complexity of cosmological perturbations in different models of the early universe. A natural measure for the complexity of cosmological perturbations is based on the symplectic group, allowing us to identify complexity with geodesics in the hyperbolic plane. We investigate the complexity of both the mode functions and the physical perturbations, arguing that the latter often provides a more insightful description of the physics involved. In all models the total complexity reached is rather large. Inflationary perturbations may be represented by a comparatively simple quantum circuit, while the perturbations during a matter-dominated contracting phase present the most rapid growth in complexity. Ekpyrotic perturbations reside in the middle and are distinguished by the smallest growth of complexity before horizon exit. Our analysis serves to highlight how different cosmological models achieve the same end result for the perturbations via different routes and how all models show a pronounced sensitivity to initial conditions.

We present a scenario of vector dark matter production from symmetry breaking at the end of inflation. In this model, the accumulated energy density associated with the quantum fluctuations of the dark photon accounts for the present energy density of dark matter. The inflaton is a real scalar field while a heavy complex scalar field, such as the waterfall of hybrid inflation, is charged under the dark gauge field. After the heavy field becomes tachyonic at the end of inflation, rolling rapidly toward its global minimum, the dark photon acquires mass via the Higgs mechanism. To prevent the decay of the vector field energy density during inflation, we introduce couplings between the inflaton and the gauge field such that the energy is pumped to the dark sector. The setup can generate the observed dark matter abundance for a wide range of the dark photon’s mass and with the reheat temperature around ${10}^{12}\mathrm{GeV}$. The model predicts the formation of cosmic strings at the end of inflation with the tensions which are consistent with the CMB upper bounds.

We propose a new model of Bayesian neural networks to not only detect the events of compact binary coalescence in the observational data of gravitational waves (GW) but also identify the full length of the event duration including the inspiral stage. This is achieved by incorporating the Bayesian approach into the convolutional, long short-term memory, fully connected deep neural network classifier, which integrates together the convolutional neural network (CNN) and the long short-term memory recurrent neural network (LSTM). Our model successfully detect all seven binary black hole events in the LIGO Livingston O2 data, with the periods of their GW waveforms correctly labeled. The ability of a Bayesian approach for uncertainty estimation enables a newly defined ‘awareness’ state for recognizing the possible presence of signals of unknown types, which is otherwise rejected in a non-Bayesian model. Such data chunks labeled with the awareness state can then be further investigated rather than overlooked. Performance tests with 40,960 training samples against 512 chunks of 8-second real noise mixed with mock signals of various optimal signal-to-noise ratio $0\le {\rho }_{\mathrm{opt}}\le 18$ show that our model recognizes 90% of the events when ${\rho }_{\mathrm{opt}}>7$ (100% when ${\rho }_{\mathrm{opt}}>8.5$) and successfully labels more than 95% of the waveform periods when ${\rho }_{\mathrm{opt}}>8$. The latency between the arrival of peak signal and generating an alert with the associated waveform period labeled is only about 20 seconds for an unoptimized code on a moderate GPU-equipped personal computer. This makes our model possible for nearly real-time detection and for forecasting the coalescence events when assisted with deeper training on a larger dataset using the state-of-art HPCs.

We assess the occurrence of fast neutrino flavor instabilities in two three-dimensional state-of-the-art core-collapse supernova simulations performed using a two-moment three-species neutrino transport scheme: one with an exploding $9{\mathrm{M}}_{\odot }$ and one with a nonexploding $20{\mathrm{M}}_{\odot }$ model. Apart from confirming the presence of fast instabilities occurring within the neutrino decoupling and the supernova pre-shock regions, we detect flavor instabilities in the post-shock region for the exploding model. These instabilities are likely to be scattering-induced. In addition, the failure in achieving a successful explosion in the heavier supernova model seems to seriously hinder the occurrence of fast instabilities in the post-shock region. This is a consequence of the large matter densities behind the stalled or retreating shock, which implies high neutrino scattering rates and thus more isotropic distributions of neutrinos and antineutrinos. Our findings suggest that the supernova model properties and the fate of the explosion can remarkably affect the occurrence of fast instabilities. Hence, a larger set of realistic hydrodynamical simulations of the stellar collapse is needed in order to make reliable predictions on the flavor conversion physics.

Binary black holes (BBHs) can form from the collapsed cores of isolated high-mass binary stars. The masses and spins of these BBHs are determined by the complicated interplay of phenomena such as tides, winds, accretion, common-envelope evolution (CEE), supernova natal kicks, and stellar core-envelope coupling. The gravitational waves emitted during the mergers of BBHs depend on their masses and spins and can thus constrain these phenomena. We present a simplified model of binary stellar evolution and identify regions of the parameter space that produce BBHs with large spins misaligned with their orbital angular momentum. In Scenario A [B] of our model, stable mass transfer (SMT) occurs after Roche-lobe overflow (RLOF) of the more [less] massive star, while CEE follows RLOF of the less [more] massive star. Each scenario is further divided into Pathways 1 and 2 depending on whether the core of the more massive star collapses before or after RLOF of the less massive star, respectively. If the stellar cores are coupled weakly to their envelopes, highly spinning BBHs can be produced if natal spins greater than 10% of the breakup value are inherited from the stellar progenitors. BBHs can alternatively acquire large spins by tidal synchronization during the Wolf-Rayet stage in Scenario A or by accretion onto the initially more massive star during SMT in Scenario B. BBH spins can be highly misaligned if the kicks are comparable to the orbital velocity, which is more easily achieved in Pathway A1, where the kick of the more massive star precedes CEE.

We study the well-motivated mixed dark matter (DM) scenario composed of a dominant thermal WIMP, highlighting the case of $SU(2{)}_L$ triplet fermion “winos,” with a small fraction of primordial black holes (PBHs). After the wino kinetic decoupling, the DM particles are captured by PBHs leading to the presence of PBHs with dark minihalos in the Milky Way today. The strongest constraints for the wino DM come from the production of narrow line gamma rays from wino annihilation in the Galactic Center. We analyse in detail the viability of the mixed wino DM scenario, and determine the constraints on the fraction of DM in PBHs assuming a cored halo profile in the Milky Way. We show that already with the sensitivity of current indirect searches, there is a significant probability for detecting a gamma ray signal characteristic for the wino annihilation in a single nearby dressed PBH when $M_{\mathrm{PBH}}\sim M_{\odot }$, which we refer to as a “shining black hole.” Similar results should apply also in more general setups with ultracompact minihalos or other DM models, since the accretion of DM around large overdensities and DM annihilation are both quite generic processes.

We study the resonance contributions for the kaon pair originating from the intermediate states $\rho (770,1450,1700)$ and $\omega (782,1420,1650)$ for the three-body hadronic decays $B\to K\overline{K}h$ in the perturbative QCD approach, where $h=(\pi ,K)$. The branching fractions of the virtual contributions for $K\overline{K}$ from the Breit-Wigner formula tails of $\rho (770)$ and $\omega (782)$, which have been ignored in experimental and theoretical studies for these decays, are found larger than the corresponding contributions from the resonances $\rho (1450,1700)$ and $\omega (1420,1650)$. The differential branching fractions for $B\to \rho (770)h\to K\overline{K}h$ and $B\to \omega (782)h\to K\overline{K}h$ are found nearly unaffected by the quite different values of the full widths for $\rho (770)$ and $\omega (782)$ in this paper. The predictions in this work for the branching fractions of the quasi-two-body decays $B^{+}\to {\pi }^{+}\rho (1450{)}^0\to {\pi }^{+}{K}^{+}{K}^{-}$ and $B^{+}\to {\pi }^{+}\rho (1450{)}^0\to {\pi }^{+}{\pi }^{+}{\pi }^{-}$ meet the requirement of $SU(3)$ symmetry relation.

We develop the effective field theory of diffusive Nambu-Goldstone (NG) modes associated with spontaneous internal symmetry breaking taking place in nonequilibrium open systems. The effective Lagrangian describing semiclassical dynamics of the NG modes is derived and matching conditions for low-energy coefficients are also investigated. Due to new terms peculiar to open systems, the associated NG modes show diffusive gapless behaviors in contrast to the propagating NG mode in closed systems. We demonstrate two typical situations relevant to the condensed matter physics and high-energy physics, where diffusive type-A or type-B NG modes appear.

Effective theories are well established theoretical frameworks to describe the effect of energetically widely separated UV models on observables at lower energy scales. Due to the complexity of the effective theory when taking all the Standard Model symmetries and degrees of freedom into account, tensioning the entire system in a completely agnostic way against experimental measurements results in constraints on the Wilson coefficients of the effective operators that either bears little information or challenge intrinsic assumptions imposed on the effective field theory framework. In general, a specific high-scale extension of the Standard Model only induces a subset of all possible operators. Thus, by investigating which operators are induced by different classes of the Standard Model extensions and comparing to which precision observables they contribute, we show that it is possible to obtain an improved understanding of which UV model is realised in nature. We present the $\mathrm{tree}+1$-loop matching results for dimension-6 operators of 15 different BSM scenarios onto SMEFT, and also including, the specific model-based contributions to the observables. We argue that more observables and matching with higher theoretical precision will pave the way to distinguish the single scalar extensions of the SM signatures uniquely. We promote this approach to study new sets of observables in the context of current and near future experiments.

In detecting neutrinos from the Large Hadron Collider, $\mathrm{FASER}\nu$ will record the most energetic laboratory neutrinos ever studied. While charged current neutrino scattering events can be cleanly identified by an energetic lepton exiting the interaction vertex, neutral current interactions are more difficult to detect. We explore the potential of $\mathrm{FASER}\nu$ to observe neutrino neutral current scattering $\nu N\to \nu N$, demonstrating techniques to discriminate neutrino scattering events from neutral hadron backgrounds as well as to estimate the incoming neutrino energy given the deep inelastic scattering final state. We find that deep neural networks trained on kinematic observables allow for the measurement of the neutral current scattering cross section over neutrino energies from 100 GeV to several TeV. Such a measurement can be interpreted as a probe of neutrino nonstandard interactions that is complementary to limits from other tests, such as oscillations and coherent neutrino-nucleus scattering.

The QCD axion remains experimentally viable in the mass range of $\mathcal{O}(10\mathrm{MeV})$ if (i) it couples predominantly to the first generation of SM fermions; (ii) it decays to $e^{+}{e}^{-}$ with a short lifetime ${\tau }_a\lesssim 4\times {10}^{-14}\mathrm{s}$; and (iii) it has suppressed isovector couplings, i.e., if it is piophobic. Remarkably, these are precisely the properties required to explain recently observed anomalies in nuclear deexcitations, to wit: the $e^{+}{e}^{-}$ emission spectra of isoscalar magnetic transitions of ${}^8\mathrm{Be}$ and ${}^4\mathrm{He}$ nuclei showed a “bumplike” feature peaked at $m_{e^{+}{e}^{-}}\sim 17\mathrm{MeV}$. In this paper, we argue that on-shell emission of the QCD axion (with the aforementioned properties) provides an extremely well-motivated, compatible explanation for the observed excesses in these nuclear deexcitations. The absence of anomalous features in other measured transitions is also naturally explained: piophobic axion emission is strongly suppressed in isovector magnetic transitions and forbidden in electric transitions. This QCD axion hypothesis is further corroborated by an independent observation: a $\sim 2–3\sigma$ deviation in the measurement of $\mathrm{\Gamma }({\pi }^0\to e^{+}{e}^{-})$ from the Standard Model theoretical expectation. This paper also includes detailed estimations of various axionic signatures in rare light meson decays, which take into account contributions from low-lying QCD resonance exchange, and, in the case of rare kaon decays, the possible effective implementations of $\mathrm{\Delta }S=1$ octet enhancement in chiral perturbation theory. These inherent uncertainties of the effective description of the strong interactions at low energies result in large variations in the predictions for hadronic signals of the QCD axion; in spite of this, the estimated ranges for rare meson decay rates obtained here can be probed in the near future in $\eta /{\eta }^{\prime }$ and kaon factories.

We present the analysis of a new signature for light dark matter detection with superfluid ${}^4\mathrm{He}$: the emission of three phonons. We show that, in a region of mass below the MeV, the kinematics of this process can offer a way to reconstruct the dark matter interaction vertex while providing background rejection via coincidence requirements and directionality. We develop all the theoretical tools to deal with such an observable, and compute the associated differential distributions.