The gravitational shock waves have provided crucial insights into entanglement structures of black holes in the $\mathrm{AdS}/\mathrm{CFT}$ correspondence. Recent progress on the soft hair physics suggests that these developments from holography may also be applicable to geometries beyond negatively curved spacetime. In this work, we derive a simple thermodynamic relation which relates the gravitational shock wave to a microscopic area deformation. Our treatment is based on the covariant phase space formalism and is applicable to any Killing horizon in generic static spacetime which is governed by arbitrary covariant theory of gravity. The central idea is to probe the gravitational shock wave, which shifts the horizon in the $u$ direction, by the Noether charge constructed from a vector field which shifts the horizon in the $v$ direction. As an application, we illustrate its use for the Gauss-Bonnet gravity. We also derive a simplified form of the gravitational scattering unitary matrix and show that its leading-order contribution is nothing but the exponential of the horizon area: $\mathcal{U}=\exp (i\text{Area})$.

Starting with a first-order derivative in a self-dual model which describes a massive spin-4 mode in $D=2+1$ dimensions, we obtain a sequence of three more new descriptions, which then gives us an interconnected self-dual chain $SD(i)$ with $i=1$, 2, 3, 4 indicating the order in derivatives. We demonstrate that a powerful notation in terms of a self-adjoint operator $\mathrm{\Omega }$ in the framelike scenario truly simplifies the investigation for new models, and at the third-order level can be converted to a geometrical description in terms of the much more usual totally symmetric double traceless field.

We consider unconstrained formulation of the higher spin gauge theory in anti–de Sitter (AdS) spacetime, given by actions [A. Y. Segal, arXiv:0103028; M. Najafizadeh, Phys. Rev. D 98, 125012 (2018)], and provide on-shell supersymmetry transformations for the $\mathcal{N}=1$ unconstrained massless higher spin supermultiplet in four-dimensional ${\mathrm{AdS}}_4$. Such an irreducible supermultiplet $({\mathrm{\Phi }}_1,{\mathrm{\Phi }}_2;{\mathrm{\Psi }}_1,{\mathrm{\Psi }}_2)$ contains a pair of bosonic fields, with opposite parity, which are generating functions (infinite collection of totally symmetric real tensor fields of all integer rank $s=0,1,\dots ,\infty$), as well as two fermionic fields, which have opposite signs of the AdS radius, that are spinorial generating functions (infinite tower of totally symmetric Majorana spinor-tensor fields of all half-integer spin $s=\frac{1}{2},\frac{3}{2},\dots ,\infty$).

The gravitational radiation from the ringdown of a binary black hole merger is described by the solution of the Teukolsky equation, which predicts both the temporal dependence and the angular distribution of the emission. Many studies have explored the temporal feature of the ringdown wave through black hole spectroscopy. In this work, we further study the spatial distribution, by introducing a global fitting procedure over both temporal and spatial dependencies, to propose a more complete test of general relativity. We show that spin-weighted spheroidal harmonics are the better representation of the ringdown angular emission patterns compared to spin-weighted spherical harmonics. The differences are distinguishable in numerical relativity waveforms. We also study the correlation between progenitor binary properties and the excitation of quasinormal modes, including higher-order angular modes, overtones, prograde, and retrograde modes. Specifically, we show that the excitation of retrograde modes is dominant when the remnant spin is antialigned with the binary orbital angular momentum. This study seeks to provide an analytical strategy and inspire the future development of ringdown tests using real gravitational wave events.

We consider a higher-derivative generalization of disformal transformations in $D$-dimensional spacetime and clarify the conditions under which they form a group with respect to the matrix product and the functional composition. These conditions allow us to systematically construct the inverse transformation in a fully covariant manner. Applying the invertible generalized disformal transformation to known ghost-free scalar-tensor theories, we obtain a novel class of ghost-free scalar-tensor theories, whose action contains the third- or higher-order derivatives of the scalar field as well as nontrivial higher-order derivative couplings to the curvature tensor.

The collisional Penrose process received much attention when Bañados, Silk, and West (BSW) pointed out the possibility of test-particle collisions with arbitrarily high center-of-mass energy in the vicinity of the horizon of an extremally rotating black hole. However, the energy that can be extracted from the black hole in this promising, if simplified, scenario, called the BSW effect, turned out to be subject to unconditional upper bounds. And although such bounds were not found for the electrostatic variant of the process, this version is also astrophysically unfeasible, since it requires a maximally charged black hole. In order to deal with these deficiencies, we revisit the unified version of the BSW effect concerning collisions of charged particles in the equatorial plane of a rotating electrovacuum black hole spacetime. Performing a general analysis of energy extraction through this process, we explain in detail how the seemingly incompatible limiting cases arise. Furthermore, we demonstrate that the unconditional upper bounds on the extracted energy are absent for arbitrarily small values of the black hole electric charge. Therefore, our setup represents an intriguing simplified model for possible highly energetic processes happening around astrophysical black holes, which may spin fast but can have only a tiny electric charge induced via interaction with an external magnetic field.

We explore a curious but simple variant of the Bronnikov-Ellis wormhole spacetime with a specific “red-shift function” (i.e. $g_{00}$) in the line element. The matter required to support such a geometry violates the local null energy condition (NEC) only around the throat and the global averaged NEC integral along radial null geodesics may be adjusted to arbitrarily small negative values, using metric parameters. Properties of the line element manifest in the metric functions, curvature and the required matter stress energy are delineated. Further, exact null and timelike geodesics are found and generic features of periodic/nonperiodic motion (closed, bounded or open) are presented. Scalar wave propagation is also solved analytically, thereby providing a partial check on the stability of the geometry under scalar perturbations. Interestingly, we note that this Bronnikov-Ellis variant may be viewed as a four dimensional, timelike section of a five dimensional, static, nonvacuum, Witten bubblelike geometry which, with an extra dimension, also has wormhole features and is threaded by matter satisfying the NEC.

The Lorentzian Engle-Pereira-Rovelli-Livine/Freidel-Krasnov spinfoam model and the Conrady-Hnybida timelike-surface extension can be expressed in the integral form $\int e^S$. This work studies the analytic continuation of the spinfoam action $S$ to the complexification of the integration domain. Our work extends our knowledge from the real critical points well-studied in the spinfoam large-$j$ asymptotics to general complex critical points of $S$ analytic continued to the complex domain. The complex critical points satisfy critical equations of the analytic continued $S$. In the large-$j$ regime, the complex critical points give subdominant contributions to the spinfoam amplitude when the real critical points are present. But the contributions from the complex critical points can become dominant when the real critical points are absent. Moreover, the contributions from the complex critical points cannot be neglected when the spins $j$ are not large. In this paper, we classify the complex critical points of the spinfoam amplitude and find a subclass of complex critical points that can be interpreted as four-dimensional simplicial geometries. In particular, we identify the complex critical points corresponding to the Riemannian simplicial geometries although we start with the Lorentzian spinfoam model. The contribution from these complex critical points of Riemannian geometry to the spinfoam amplitude give $e^{-S_{\text{Regge}}}$ in analogy with the Euclidean path integral, where $S_{\text{Regge}}$ is the Riemannian Regge action on the simplicial complex.

In this paper, using the quasilocal formalism of Brown and York, the flow of energy through a closed surface containing a gravitating physical system is calculated in a way that augments earlier results on the subject by Booth and Creighton. To this end, by performing a variation of the total gravitational Hamiltonian (bulk plus boundary part), it is shown that associated tidal heating and deformation effects generally are larger than expected. This is because the aforementioned variation leads to previously unrecognized correction terms, including a bulk-to-boundary inflow term that does not appear in the original calculation of the time derivative of the Brown-York energy and leads to corrective extensions of Einstein’s quadrupole formula in the large sphere limit.

We study the nonlinear evolution of the spherical symmetric charged black holes under a small neutral scalar field perturbation in Einstein-Maxwell-dilaton theory with coupling function $f(\varphi )=e^{-b\varphi }$ in asymptotic anti–de Sitter spacetime. The nonminimal coupling between scalar and Maxwell fields allows the transmission of the energy from the Maxwell field to the scalar field, but also behaves as a repulsive force for the scalar. The scalar field oscillates with damping amplitude and converges to a final value. The irreducible mass of the black hole increases abruptly at initial times and then saturates to the final value exponentially. The saturating rate is twice the decaying rate of the dominant mode of the scalar. The effects of the black hole charge, the cosmological constant, and the coupling parameter on the evolution are studied in detail. When the initial configuration is a naked singularity spacetime with a large charge to mass ratio, a horizon will form soon and hide the singularity.

We investigate the retrolensing of sunlight reflected by a photon sphere and by a potential barrier near an antiphoton sphere around a Reissner-Nordström naked singularity. We apply the deflection angles of the light rays in strong deflection limits to the retrolensing. We show that the retrolensing by the photon sphere around the Reissner-Nordström naked singularity can be brighter than the one around a Reissner-Nordström black hole because of the rays reflected by the potential barrier.

We compute the equilibrium, the fundamental eigenfrequency of oscillations modes, and quadrupolar tidal deformability of anisotropic polytropic spheres. These studies are, respectively, performed through the numerical solution of the Tolman-Oppenheimer-Volkoff equation, Chandrasekhar radial oscillation equations, and nonlinear first-order Riccati equation for tidal deformability, all modified from their original version to include the anisotropic effects. For the polytropic exponent $\gamma =2$ and the anisotropic model of Cattoen, Faber, and Visser, we show that the anisotropy could be reflected in the radial pressure, energy density, speed of sound, radial stability, and tidal deformability.

We investigate the cosmological aspects of the most general parity preserving Metric-Affine Gravity theory quadratic in torsion and nonmetricity in the presence of a cosmological hyperfluid. The equations of motion are obtained by varying the action with respect to the metric and the independent affine connection. Subsequently, considering a Friedmann-Lemaître-Robertson-Walker background, we derive the most general form of the modified Friedmann equations for the full quadratic theory. We then focus on a characteristic subcase involving only two quadratic contributions given in terms of torsion and nonmetricity vectors. In this setup, studying the modified Friedmann equations along with the conservation laws of the perfect cosmological hyperfluid, we provide exact solutions both for purely dilation and for purely spin hypermomentum sources. We then discuss the physical consequences of our model and the prominent role of torsion and nonmetricity in this cosmological setup.

We derive an exact wormhole spacetime supported by a phantom scalar field in the context of $f(\mathsf{R})$ gravity theory. Without specifying the form of the $f(\mathsf{R})$ function, the scalar field self-interacts with a mass term potential which is derived from the scalar equation and in the resulting $f(\mathsf{R})$ model the scalar curvature is modified by the presence of the scalar field and it is free of ghosts and avoids the tachyonic instability.

Blazars are a class of active galactic nuclei that host relativistic jets oriented close to the observer’s line of sight. Blazars have very complex variability properties. Flares, namely flux variations around the mean value with a well-defined shape and duration, are one of the identifying properties of the blazar phenomenon. Blazars are known to exhibit multiwavelength flares, but also “orphan” flares, namely flux changes that appear only in a specific energy range. Various models, sometimes at odds with each other, have been proposed to explain specific flares even for a single source, and cannot be synthesized into a coherent picture. In this paper, we propose a unified model for explaining orphan and multiwavelength flares from blazars in a common framework. We assume that the blazar emission during a flare consists of two components: (i) a quasistable component that arises from the superposition of numerous but comparatively weak dissipation zones along the jet, forming the background (low-state) emission of the blazar, and (ii) a transient component, which is responsible for the sudden enhancement of the blazar flux, forming at a random distance along the jet by a strong energy dissipation event. Whether a multiwavelength or orphan flare is emitted depends on the distance from the base of the jet where the dissipation occurs. Generally speaking, if the dissipation occurs at a small/large distance from the supermassive black hole, the inverse Compton/synchrotron radiation dominates and an orphan $\gamma$-ray/optical flare tends to appear. On the other hand, we may expect a multiwavelength flare if the dissipation occurs at an intermediate distance. We show that the model can successfully describe the spectral energy distribution of different flares from the flat spectrum radio quasar 3C 279 and the BL Lacertae object PKS 2155-304.

I investigate the roles of cluster dynamics and massive binary evolution in producing stellar-remnant binary black hole (BBH) mergers over the cosmic time. To that end, dynamical BBH mergers are obtained from long-term direct N-body evolutionary models of $\sim {10}^4{M}_{\odot }$, pc-scale young massive clusters (YMC) evolving into moderate-mass open clusters. Fast evolutionary models of massive isolated binaries yield BBHs from binary evolution. Population synthesis in a Model Universe is then performed, taking into account observed cosmic star formation and enrichment histories, to obtain BBH-merger yields from these two channels observable at the present day and over cosmic time. The merging BBH populations from the two channels are combined by applying a proof-of-concept Bayesian regression chain, taking into account observed differential intrinsic BBH merger rate densities from the second gravitational-wave transient catalog (GWTC-2). The analysis estimates an OB-star binary fraction of $f_{\mathrm{Obin}}\gtrsim 90\%$ and a YMC formation efficiency of $f_{\mathrm{YMC}}\sim {10}^{-2}$, being consistent with recent optical observations and large scale structure formation simulations. The corresponding combined Model Universe present-day, differential intrinsic BBH merger rate density and the cosmic evolution of BBH merger rate density both agree well with those from GWTC-2. The analysis also suggests that despite significant “dynamical mixing” at low redshifts, BBH mergers at high redshifts ($z_{\text{event}}\gtrsim 1$) could still be predominantly determined by binary-evolution physics. Caveats in the present approach and future improvements are discussed.

The diffuse $\gamma$-ray spectrum at sub-PeV energy region has been measured for the first time by the Tibet-$\mathrm{AS}\gamma$ experiment. It will shed new light on the understanding of the origin and propagation of Galactic cosmic rays at very high energies. It has been pointed out that the traditional cosmic ray propagation model based on low energy measurements undershoot the new data, and modifications of the model with new ingredients or alternative propagation framework is required. In this work, we propose that the hadronic interactions between freshly accelerated cosmic rays and the medium surrounding the sources, which was neglected in the traditional model, can naturally account for the Tibet-$\mathrm{AS}\gamma$ diffuse emission. We show that this scenario gives a consistent description of other secondary species such as the positron spectrum, the boron-to-carbon ratio, and the antiproton-to-proton ratio. As a result, the electron spectrum above 10 TeV will have a hardening due to this secondary component, which may be tested by future measurements.

This paper presents a combined analysis of the potential of a future electron-positron collider to constrain the Higgs, top, and electroweak sectors of the Standard Model effective field theory. The leading contributions of operators involving top quarks arise mostly at one-loop suppressed order and can be captured by the renormalization group mixing with Higgs operators. We perform global fits with an extended basis of 29 parameters, including both Higgs and top operators, to the projections for the Higgs, top, and electroweak precision measurements at the International Linear Collider (ILC). The determination of the Higgs boson couplings in the 250 GeV stage of the ILC is initially severely degraded by the additional top-quark degrees of freedom, but can be nearly completely recovered by the inclusion of precise measurements of top-quark EW couplings at the LHC. The physical Higgs couplings are relatively robust, as the top mass is larger than the energy scale of electroweak processes. The effect of the top operators on the bounds on the Wilson coefficients is much more pronounced and may limit our ability to identify the source of deviations from the Standard Model. Robust global bounds on all Wilson coefficients are only obtained when the 500 GeV stage of the ILC is included.

We study the nonleptonic charmless $B_{u,d,s}\to K_0^{*}(1430)P$ ($P=K$, $\pi$) and $K_0^{*}(1430)V$ $(V=K^{*},\rho ,\omega ,\varphi )$ decays. The amplitudes are calculated within the QCD factorization, and the nonperturbative quantities are evaluated by using a covariant light-front approach. The branching fractions and $CP$ asymmetries of theses decay modes are calculated, some decay modes are first predicted, and some useful relations based on $SU(3)$ flavor symmetry are discussed. Comparing the theoretical results with the current available experimental data, it is found that $K_0^{*}(1430)$ can be described as the lowest-lying p-wave $(s,u/d)$ state rather than the first excited one.

In this work, we investigate the existence of analytic solutions of static scalar fields on Lifshitz spacetimes. We evade Derrick’s theorem on curved spacetimes by breaking general covariance and use first-order formalism to obtain solutions with finite energy related to the time-translational invariance of the background geometry along with the energy-momentum tensor of the model. We show that such solutions exist and are stable in systems where the Lifshitz background geometry is fixed and the self-interaction potential of the scalar field explicitly depends on the radial coordinate present in the metric.