We investigate scalar-tensor theories, motivated by dark energy models, in the strong gravity regime around the black hole at the center of our galaxy. In such theories general relativity is modified since the scalar field couples to matter. We consider the most general conformal and disformal couplings of the scalar field to matter to study the orbital behavior of the nearby stars around the galactic star center $Sgr{A}^{*}$. Markov chain Monte Carlo simulation yields a bound on the parameters of the couplings of the scalar field to matter. Using Bayesian analysis yields the first constraints on such theories in the strong gravity regime.

We study generalizations of the Schwarzschild-de Sitter solution in the presence of a scalar field with a potential barrier. These static, spherically symmetric solutions have two horizons, in between which the scalar interpolates at least once across the potential barrier, thus developing a lump. In part, we recover solutions discussed earlier in the literature, and for those, we clarify their properties. But we also find a new class of solutions in which the scalar lump curves the spacetime sufficiently strongly so as to change the nature of the erstwhile cosmological horizon into an additional trapped horizon, resulting in a scalar lump surrounded by two black holes. These new solutions appear in a wide range of the parameter space of the potential. We also discuss (challenges for) the application of all of these solutions to black hole seeded vacuum decay.

We study conserved charges and thermodynamics of analytic rotating anti–de Sitter black holes with extended horizon topology—also known as black strings—in dynamical Chern-Simons modified gravity. The solution is supported by a scalar field with an axionic profile that depends linearly on the coordinate that spans the string. We compute conserved charges by making use of the renormalized boundary stress-energy tensor. Then, by adopting the Noether-Wald formalism, we compute the black string entropy and obtain its area law. Indeed, the reduced Euclidean Hamiltonian approach shows that these methods yield a consistent first law of thermodynamics. Additionally, we derive a Smarr formula using a radial conservation law associated to the scale invariance of the reduced action and obtain a Cardy formula for the black string. A first-order phase transition takes place at a critical temperature between the ground state and the black string, above which the black string is the thermodynamically favored configuration.

We compare the optical appearance of a thin accretion disk in the Simpson-Visser spacetime to the Schwarzschild black hole case in this paper. We calculate and illustrate the redshift and observed flux distributions as viewed by distant observers at various inclination angles. Simpson-Visser family of metrics creates Novikov-Thorne (NT) accretion disks images that nearly look like a Schwarzschild black hole’s NT accretion disk. We have studied also the embedding diagram, the electromagnetic properties of the accretion disk such as the temperature and the radiation flux of the energy by the accretion disk and the accretion efficiency. Compared to the Schwarzschild black hole, we find that the temperature, radiation flux of the energy, and the luminosity of the accretion disk increase by increasing the regularization parameter $l$. We conclude that, based on astrophysical observational signatures in the properties of the electromagnetic spectrum, we can distinguish the wormhole geometries from the regular black holes (black-bounce) and the Schwarzschild black hole.

Deep learning algorithms have gained importance in particle physics in the last few years. They have been shown to outperform traditional strategies in particle identification, tracking and energy reconstruction in the most modern high-energy physics experiments. The attractive feature of these techniques is their ability to model large dimensionality inputs and catch nontrivial correlations among the variables, which could be hidden or not easy to model. This paper focuses on the application of deep neural networks to the event reconstruction of the Limadou High-Energy Particle Detector on board the China Seismo-Electromagnetic Satellite. The core of the reconstruction chain is a set of fully connected neural networks that reconstructs the nature, the arrival direction and the kinetic energy of incoming electrons and protons, starting from the signals recorded in the detector. These networks are trained on a dedicated Monte Carlo simulation as representative as possible of real data. We describe the simulation, architecture and methodology adopted to design and train the networks, and finally report on the performance measured on simulated and flight data.

We consider the propagation of nonlinear sound waves in a perfect fluid at rest. By employing the Riemann wave equation of nonlinear acoustics in one spatial dimension, it is shown that waves carrying a constant density perturbation at their tails produce an acoustic analogue of gravitational wave memory. For the acoustic memory, which is in general nonlinear, the nonlinearity of the effective spacetime dynamics is not due to the Einstein equations, but due to the nonlinearity of the perfect fluid equations. For concreteness, we employ a box-trapped Bose-Einstein condensate, and suggest an experimental protocol to observe acoustic gravitational wave memory.

We revisit the contribution of axial-vector mesons to the hyperfine splitting of muonic hydrogen. We focus our attention on the doubly-virtual asymptotic behavior of the relevant form factors of axial-vector mesons, together with their coupling to nucleons based on resonance saturation and short-distance constraints. Among others, we find significant differences with respect to previous studies, including an opposite sign and a $\sim 50\%$ effect of the doubly-virtual high-energy behavior.

We consider a chiral gauge theory from which light composite Dirac neutrinos dynamically emerge, augmented by a QCD axion to solve the strong $CP$ problem. We show that an interplay between the composite sector and the axion can also simultaneously lead to successful baryogenesis and generate a correct dark matter abundance via “cogenesis” without contradicting present constraints. We predict $\mathrm{\Delta }{N}_{\mathrm{eff}}\ge 0.14$ and $m_a$ in the range $O(10)\mu \mathrm{eV}–O(10)\mathrm{meV}$, which can be firmly tested by upcoming CMB experiments and axion searches.

In light of recent discrepancies between the modeling of $t\overline{t}{W}^{\pm }$ signatures and measurements reported by the LHC experimental collaborations, we investigate in detail theoretical uncertainties for multilepton signatures. We compare results from the state-of-the-art full off-shell calculation and its narrow-width approximation to results obtained from the on-shell $t\overline{t}{W}^{\pm }$ calculation, with approximate spin correlations in top-quark and $W$ decays, matched to parton showers. In the former case double-, single-, and nonresonant contributions together with interference effects are taken into account, while the latter two cases are only based on the double-resonant top-quark contributions. The comparison is performed for the LHC at $\sqrt{s}=13\mathrm{TeV}$ for which we study separately the multilepton signatures as predicted from the dominant next-to-leading-order (NLO) contributions at the perturbative orders $\mathcal{O}({\alpha }_s^3{\alpha }^6)$ and $\mathcal{O}({\alpha }_s{\alpha }^8)$. Furthermore, we combine both contributions and propose a simple way to approximately incorporate the full off-shell effects in the NLO computation of on-shell $pp\to t\overline{t}{W}^{\pm }$ matched to parton showers.

Bottomonium states are key probes for experimental studies of the quark-gluon plasma (QGP) created in high-energy nuclear collisions. Theoretical models of bottomonium productions in high-energy nuclear collisions rely on the in-medium interactions between the bottom and antibottom quarks. The latter can be characterized by the temperature ($T$) dependent potential, with real ($V_R(T,r)$) and imaginary ($V_I(T,r)$) parts, as a function of the spatial separation ($r$). Recently, the masses and thermal widths of up to $3S$ and $2P$ bottomonium states in QGP were calculated using lattice quantum chromodynamics (LQCD). Starting from these LQCD results and through a novel application of deep neural network, here, we obtain $V_R(T,r)$ and $V_I(T,r)$ in a model-independent fashion. The temperature dependence of $V_R(T,r)$ was found to be very mild between $T\approx 0–334\mathrm{MeV}$. For $T=151–334\mathrm{MeV}$, $V_I(T,r)$ shows a rapid increase with $T$ and $r$, which is much larger than the perturbation-theory-based expectations.

In this article, we perform a sensitivity study of an unbinned angular analysis of the $B\to D^{*}\ell {\nu }_{\ell }$ decay, including the contributions from the right-handed current. We show that the angular observable can constrain very strongly the right-handed current without the intervention of the yet unsolved $V_{cb}$ puzzle.

Using $J/\psi$ radiative decays from 9.0 billion $J/\psi$ events collected by the BESIII detector, we search for di-muon decays of a $CP$-odd light Higgs boson ($A^0$), predicted by many new physics models beyond the Standard Model, including the next-to-minimal supersymmetric Standard Model. No evidence for the $CP$-odd light Higgs production is found, and we set 90% confidence level upper limits on the product branching fraction $\mathcal{B}(J/\psi \to \gamma A^0)\times \mathcal{B}(A^0\to {\mu }^{+}{\mu }^{-})$ in the range of $(1.2-778.0)\times {10}^{-9}$ for $0.212\le m_{A^0}\le 3.0\mathrm{GeV}/c^2$. The new measurement is a 6–7 times improvement over our previous measurement, and is also slightly better than the BABAR measurement in the low-mass region for $\tan \beta =1$.

It has been argued that ultracompact objects, which possess light rings but no horizons, may be unstable against gravitational perturbations. To test this conjecture, we revisit the quasiblack hole solutions, a family of horizonless spacetimes whose limit is the extremal Reissner-Nordström black hole. We find a critical parameter at which the light rings just appear. We then calculate the quasinormal modes of the quasiblack holes. Both the WKB result and the numerical result show that long-lived modes survive for the range where light rings exist, indicating that horizonless spacetimes with light rings are unstable. Our work provides a strong and explicit example that light rings could be direct observational evidence for black holes.

In recent years, gravitational-wave astronomy has motivated increasingly accurate perturbative studies of gravitational dynamics in compact binaries. This in turn has enabled more detailed analyses of the dynamical black holes in these systems. For example, Pound et al. [Phys. Rev. Lett. 124, 021101 (2020)] recently computed the surface area of a Schwarzschild black hole’s apparent horizon, perturbed by an orbiting body, to second order in the binary’s mass ratio. In this paper, we take that as the starting point for a comprehensive study of a perturbed Schwarzschild black hole’s apparent and event horizon at second perturbative order, deriving generic formulas for the first- and second-order corrections to the horizons’ radial profiles, surface areas, Hawking masses, and intrinsic curvatures. We find that the two horizons are remarkably similar, and that any teleological behavior of the event horizon is suppressed in several ways. Critically, we establish that at all orders, the perturbed event horizon in a small-mass-ratio binary is effectively localized in time. Even more pointedly, the event horizon is identical to the apparent horizon at linear order regardless of the source of perturbation, implying that the seemingly teleological “tidal lead,” previously observed in linearly perturbed event horizons, is not genuinely teleological in origin. The two horizons do generically differ at second order, but their Hawking masses remain identical, implying that the event horizon obeys the same energy-flux balance law as the apparent horizon. At least in the case of a binary system, the difference between their surface areas remains extremely small even in the late stages of inspiral. In the course of our analysis, we also numerically illustrate puzzling behavior in the black hole’s motion around the binary’s center of mass.

Abstract In this paper we explore the different types of singularities that arise in the $\mathrm{\Lambda }\mathrm{CDM}$ model when dissipative processes are considered, in the framework of the Eckart’s theory. In particular, we study the late-time behavior of $\mathrm{\Lambda }\mathrm{CDM}$ model with viscous cold dark matter (CDM) and an early-time viscous radiation domination era with cosmological constant (CC). The fluids are described by the barotropic equation of state (EoS) $p=(\gamma -1)\rho$, where $p$ is the equilibrium pressure of the fluid, $\rho$ their energy density, and $\gamma$ is the barotropic index. We explore two particular cases for the bulk viscosity $\xi$, a constant bulk viscosity $\xi ={\xi }_0$, and a bulk viscosity proportional to the energy density of the fluid $\xi ={\xi }_0\rho$. Due to some previous investigations that have explored how to describe the behavior of the Universe with a negative CC, we extend our analysis to this case. We found that future singularities like Big Rip are allowed but without having a phantom EoS associated with the DE fluid. Big Crunch singularities also appears when a negative CC is present, but also de Sitter and even Big Rip types are allowed due to the negative pressure of the viscosity, which opens the possibility of an accelerated expansion in anti–de Sitter (AdS) cosmologies. We also discuss a very particular solution without Big Bang singularity that arises in the early-time radiation dominant era of our model known as soft-Big Bang.

Spontaneous scalarization is a mechanism that allows a scalar field to go undetected in weak gravity environments and yet develop a nontrivial configuration in strongly gravitating systems. At the perturbative level it manifests as a tachyonic instability around spacetimes that solve Einstein’s equations. The endpoint of this instability is a nontrivial scalar field configuration that can significantly modify a compact object’s structure and can produce observational signatures of the scalar field’s presence. Does such a mechanism exists for vector fields? Here we revisit the model that constitutes the most straightforward generalization of the original scalarization model to a vector field and perform a perturbative analysis. We show that a ghost appears as soon as the square of the naive effective mass squared becomes negative anywhere. This result poses a serious obstacle in generalizing spontaneous scalarization to vector fields.

We explore inferences on ultrahigh energy cosmic ray (UHECR) source environments—constrained by the spectrum and composition of UHECRs and nonobservation of extremely high energy neutrinos—and their implications for the observed high energy astrophysical neutrino spectrum. We find acceleration mechanisms producing power-law cosmic ray (CR) spectra $\propto E^{-2}$ are compatible with UHECR data, if CRs at high rigidities are in the quasiballistic diffusion regime as they escape their source environment. Both gas-dominated and photon-dominated source environments are able to account for UHECR observations, however photon-dominated sources give a better fit. Additionally, gas-dominated sources are in tension with current neutrino constraints. Accurate measurement of the neutrino flux at $\sim 10\mathrm{PeV}$ will provide crucial information on the viability of gas-dominated sources, as well as whether diffusive shock acceleration is consistent with UHECR observations. We also show that UHECR sources are able to give a good fit to the high energy portion of the astrophysical neutrino spectrum, above $\sim \mathrm{PeV}$. This common origin of UHECRs and high energy astrophysical neutrinos is natural if air shower data is interpreted with the sibyll2.3c hadronic interaction model, which gives the best-fit to UHECRs and astrophysical neutrinos in the same part of parameter space, but not for epos-lhc.

The low-energy chiral effective field theory of vector mesons and Goldstone bosons in an external gravitational field is considered. The energy-momentum tensor is obtained, and the gravitational form factors of the $\rho$-meson are calculated up to next-to-leading order in the chiral expansion. This amounts to considering tree-level and one-loop order diagrams. The chiral expansion of the form factors at zero momentum transfer, as well as of the slope parameters, is also performed. Also, the long-range behavior of the energy and internal force distributions is obtained and analyzed.