We study the redundancies in the global spacetime description of the eternally inflating multiverse using the quantum extremal surface prescription. We argue that a sufficiently large spatial region in a bubble universe has an entanglement island surrounding it. Consequently, the semiclassical physics of the multiverse, which is all we need to make cosmological predictions, can be fully described by the fundamental degrees of freedom associated with certain finite spatial regions. The island arises due to mandatory collisions with collapsing bubbles, whose big crunch singularities indicate redundancies of the global spacetime description. The emergence of the island and the resulting reduction of independent degrees of freedom provides a regularization of infinities which caused the cosmological measure problem.

Usually, the realizations of the noncommutative Snyder model lead to a nonassociative star product. However, it has been shown that this problem can be avoided by adding to the spacetime coordinates new tensorial degrees of freedom. The model so obtained, called the extended Snyder model, can be subject to a $\kappa$ deformation, giving rise to a unification of the Snyder and the $\kappa$-Poincaré algebras in the formalism of extended spacetime. In this paper we review this construction and consider the generic realizations of the $\kappa$-deformed extended Snyder model, calculating the associated star product, coproduct, and twist in a perturbative setting. We also introduce a representation of the Lorentz algebra in the extended space and speculate on possible interpretations of the tensorial degrees of freedom.

We study the thermodynamics of ${\mathrm{AdS}}_4$ black hole solutions of Einstein-Maxwell theory that are accelerating, rotating, and carry electric and magnetic charges. We focus on the class for which the black hole horizon is a spindle and can be uplifted on regular Sasaki-Einstein spaces to give solutions of $D=11$ supergravity that are free from conical singularities. We use holography to calculate the Euclidean on-shell action and to define a set of conserved charges which give rise to a first law. We identify a complex locus of supersymmetric and nonextremal solutions, defined through an analytic continuation of the parameters, upon which we obtain a simple expression for the on-shell action. A Legendre transform of this action combined with a reality constraint then leads to the Bekenstein-Hawking entropy for the class of supersymmetric and extremal black holes.

We consider type IIB 5-brane web diagrams for a 5D $Sp(N)$ gauge theory with an antisymmetric hypermultiplet and $N_f$ fundamental hypermultiplets. The corresponding 5-branes can be obtained by Higgsing a 5-brane web for quiver gauge theory. We use the refined topological vertex formalism to compute Nekrasov partition functions of 5D $Sp(2)$ theories with one antisymmetric hypermultiplet and flavors. Our results agree with the known results obtained from the Atiyah-Drinfeld-Hitchin-Manin method. We also discuss a particular tuning of Kähler parameters associated with this Higgsing.

We consider interacting massive scalar quantum field theory in the future Rindler wedge. This is a model example of quantum field theory in curved space-time. Using this simple example, we show how the dynamics of correlation functions depends on the choice of the initial Cauchy surface, the basis of modes, and the choice of the initial state built using the corresponding creation and annihilation operators. We show which choice of modes in the future Rindler wedge respects the Poincaré symmetry. However, we do not restrict our attention only to these modes and the corresponding ground state.

Quantum dynamics of coherent states is studied within quantum field theory using two complementary methods: by organizing the evolution as a Taylor series in elapsed time and by perturbative expansion in coupling within the interaction-picture formalism. One of the important aspects of our analysis consists in utilizing the operators and the vacuum of interacting theory in constructing the states, without invoking asymptotic particles. Focusing on a coherent state describing a spatially homogeneous field configuration, it is demonstrated that both adopted methods successfully account for nonlinear classical dynamics, giving distinguishable quantum effects. In particular, according to the time-expansion analysis the initial field acceleration, with which the field departs from its initial expectation value, is governed by the tree-level potential with renormalized mass and bare coupling constant. The interaction-picture computation, instead, can be manipulated to give the nonlinear dynamics, determined in terms of renormalized coupling and mass. However, it results in a logarithmic initial-time singularity in the field acceleration, reminiscent of the similar behavior encountered within semiclassical formalism, for certain choices of the initial state for fluctuations. Within our coherent-state analysis, the above-mentioned peculiarities are artifacts of an expansion: in the first case over infinitesimal time, while in the second case in the coupling constant. Despite this, we show that the evolution obtained within the interaction-picture analysis is valid for an extended period of time. Moreover, on top of the desired classical dynamics, it serves us with interesting quantum corrections, previously proposed by Dvali-Gomez-Zell.

Unruh-DeWitt (UDW) detectors that couple locally to a quantum field are an important tool for operationally studying field properties. Here, we study the response of an inertial UDW detector to a nonrelativistic particle state of a massive scalar field and we find that the transition probability of the detector splits into the vacuum contribution and the matter contribution. We show that the matter part oscillates with the interaction time duration and the oscillation period depends on the difference between the mass of the particle and the energy gap of the detector; a strong resonance pattern for the transition probability is found when such a difference equals zero. We compare the matter-part contribution with the nonrelativistic probability density of the particle and find that they provide qualitatively similar description of the particle.

We study the compatibility between conformal symmetry, together with unitarity, and continuous higher-form symmetries. We show that the $d$-dimensional, unitary, conformal field theories are not consistent with continuous $p$-form symmetries for certain $(d,p)$, assuming that the corresponding conserved current is a conformal primary operator. We further discuss several dynamical applications of this constraint.

Astrophysical black holes are thought to be the Kerr black holes predicted by general relativity, but macroscopic deviations from the Kerr solution can be expected from a number of scenarios involving new physics. In Paper I, we studied the reflection features in NuSTAR and XMM-Newton spectra of the supermassive black hole at the center of the galaxy MCG–06–30–15 and we constrained a set of deformation parameters proposed by Konoplya, Rezzolla, and Zhidenko (Phys. Rev. D 93, 064015, 2016). In the present work, we analyze the x-ray data of a stellar-mass black hole within the same theoretical framework in order to probe a different curvature regime. We consider a NuSTAR observation of the x-ray binary EXO 1846–031 during its outburst in 2019. As in the case of Paper I, all our fits are consistent with the Kerr black hole hypothesis, but some deformation parameters cannot be constrained well.

We present a gauge theory of the conformal group in four spacetime dimensions with a nonvanishing torsion. In particular, we allow for a completely antisymmetric torsion, equivalent by Hodge duality to an axial vector whose presence does not spoil the conformal invariance of the theory, in contrast with claims of antecedent literature. The requirement of conformal invariance implies a differential condition (in particular, a Killing equation) on the aforementioned axial vector, which leads to a Maxwell-like equation in a four-dimensional curved background. We also give some preliminary results in the context of $\mathcal{N}=1$ four-dimensional conformal supergravity in the geometric approach, showing that if we only allow for the constraint of vanishing supertorsion, all the other constraints imposed in the spacetime approach are a consequence of the closure of the Bianchi identities in superspace. This paves the way towards a future complete investigation of the conformal supergravity using the Bianchi identities in the presence of a nonvanishing (super)torsion.

Cosmological implications of a generalized Rastall theory where the nonconservation equation is promoted to accept arbitrary functions of the Ricci scalar is considered. We have obtained the model parameters of the power-law ansatz $f\propto R^{\eta }$, using $H_0$ and $f{\sigma }_8$ datasets, and show that the generalized Rastall theory could satisfy observational data. The dynamical analysis of the model shows that for $\eta \in (0,1)$, the dust dominated fixed point is lost, and as a result, the parameter range of $\eta$ should be restricted to $\eta \ge 1$. We will also show that the generalized Rastall theory will predict a universe with a stronger accelerating regime with a larger radius, compared to the $\mathrm{\Lambda }\mathrm{CDM}$ model.

We examine the thermodynamics of a new class of asymptotically anti–de Sitter (AdS) black holes with nonconstant curvature event horizons in Gauss-Bonnet Lovelock gravity, with the cosmological constant acting as thermodynamic pressure. We find that nontrivial curvature on the horizon can significantly affect their thermodynamic behavior. We observe novel triple points in six dimensions between large and small uncharged black holes and thermal AdS. For charged black holes we find a continuous set of triple points whose range depends on the parameters in the horizon geometry. We also find new generalizations of massless and negative mass solutions previously observed in Einstein gravity.

Following a recent approach, complete and analytic solutions (brane and bulk) of regular black holes are shown in a brane context. The metrics are regular both on the four-dimensional brane and in the five-dimensional bulk. Like many braneworld scenarios, the bulk spacetime is asymptotically anti–de Sitter. On the other hand, a de Sitter core on the brane avoids the singularity inside the event horizon, providing then well-known regular black holes on the brane. From the bulk perspective, the regular black holes are five-dimensional objects, with the event horizon extending to the extra dimension, but the de Sitter core is entirely on the four-dimensional brane.

In this paper, we perform first-order Sorce-Wald’s gedanken experiments to test the weak cosmic censorship conjecture (WCCC) in the higher-order gravitational theories. Based on the Noether charge method proposed by Iyer and Wald and the null energy condition of the matter fields, we derive a first-order perturbation inequality. Using this result, we find that there exists a destruction condition $S_{\mathrm{ext}}^{\prime }(r_h)<0$ for the extremal black holes under the first-order approximation of perturbation. To show the power of this condition, we evaluate the constraints given by WCCC in the quadratic and cubic gravitational theories. Our investigation implies that besides the observation requirements such as the Solar System tests, the WCCC may also play some role in the selection of physically acceptable theories.

Scalar-tensor theories whose phenomenology differs significantly from general relativity on large (e.g., cosmological) scales do not typically pass local experimental tests (e.g., in the Solar System) unless they present a suitable “screening mechanism.” An example is provided by chameleon screening, whereby the local general relativistic behavior is recovered in high-density environments, at least in weak-field and quasistatic configurations. Here, we test the validity of chameleon screening in strong-field and highly relativistic/dynamical conditions by performing fully nonlinear simulations of neutron stars subjected to initial perturbations that cause them to oscillate or even collapse to a black hole. We confirm that screened chameleon stars are stable to sufficiently small radial oscillations, but that the frequency spectrum of the latter shows deviations from the general relativistic predictions. We also calculate the scalar fluxes produced during collapse to a black hole, and we comment on their detectability with future gravitational-wave interferometers.

In the companion paper [Phys. Rev. D 103, 104010 (2021)] we have derived the short-ranged potentials for the Teukolsky equations for massless spins (0, $1/2$, 1, 2) in general spherically symmetric and static metrics. Here we apply these results to numerically compute the Hawking radiation spectra of such particles emitted by black holes (BHs) in three different ansatz: charged BHs, higher-dimensional BHs, and polymerized BHs arising from models of quantum gravity. In order to ensure the robustness of our numerical procedure, we show that it agrees with newly derived analytic formulas for the cross sections in the high and low energy limits. We show how the short-ranged potentials and precise Hawking radiation rates can be used inside the code blackhawk to predict future primordial BH evaporation signals for a very wide class of BH solutions, including the promising regular BH solutions derived from loop quantum gravity. In particular, we derive the first Hawking radiation constraints on polymerized BHs from AMEGO. We prove that the mass window $10^{16}–10^{18}\mathrm{g}$ for all dark matter into primordial BHs can be reopened with high values of the polymerization parameter, which encodes the typical scale and strength of quantum gravity corrections.

Recently, the observed equation of state for dark energy appears to favor values below $-1$. The tendency implies that the nature of dark energy may be quite different from that of the cosmological constant. In view of the adjustment on the equation of state keeps decreasing, the introduction of the phantom energy seems inevitable. By employing observational constraints from supernovae and from the acoustic scale in which the accuracy of the data has become extraordinary, we apply a phenomenological scenario to be acquainted with the evolution of our universe. The demonstration on the constrained unfolding of the phantom energy shows the model has high consistency with the current observation.

We introduce an axion-inflation model embedded in the left-right symmetric extension of the Standard Model in which $W_R$ is coupled to the axion. This model merges three milestones of modern cosmology, i.e., inflation, cold dark matter, and baryon asymmetry. Thus, it can naturally explain the observed coincidences among cosmological parameters, i.e., ${\eta }_{\mathsf{B}}\approx P_{\zeta }$ and ${\mathrm{\Omega }}_{\mathrm{DM}}\simeq 5{\mathrm{\Omega }}_{\mathsf{B}}$. The source of asymmetry is spontaneous $CP$ violation in the physics of inflation, and the lightest right-handed neutrino is the cold dark matter candidate with mass $m_{N_1}\sim 1\mathrm{GeV}$. The introduced mechanism does not rely on the largeness of the unconstrained $CP$-violating phases in the neutrino sector or fine-tuned masses for the heaviest right-handed neutrinos. It has two unknown fundamental scales, i.e., scale of inflation ${\mathrm{\Lambda }}_{\inf }=\sqrt{H{M}_{\mathrm{Pl}}}$ and left-right symmetry breaking ${\mathrm{\Lambda }}_F$. Sufficient matter asymmetry demands that ${\mathrm{\Lambda }}_{\inf }\approx {\mathrm{\Lambda }}_F$. Baryon asymmetry and dark matter today are remnants of a pure quantum effect (chiral anomaly) in inflation, which, thanks to flavor effects, has been memorized by cosmic evolution.

In the effort to define the main features a successful solution to the Hubble tension should have, growing evidence has emerged pointing to the need for models able to modify the expansion (and possibly thermal) history of the Universe both prior and after recombination, and that could thereby restore the overall concordance between early- and late-time observations without introducing or worsening other cosmological tensions in the process. In precisely this spirit, here we consider a multi-interacting dark energy model with two complementary interaction channels; one with the dark matter and one with the photons. The former most significantly affects the matter dominated epoch as well as the very late Universe, and has been shown to be able to significantly resolve the $S_8$ tension. The latter has been introduced in this work to allow for a larger and natural time dependence of the evolution of the Universe since it mostly impacts the radiation dominated epoch as well as the temperature scaling of the photons, as extensively explained in the text. As a result, considering data from $\mathrm{Planck}+\mathrm{BAO}+\mathrm{Pantheon}+\mathrm{KV}450+\mathrm{DES}$ (which can be combined since the $S_8$ value is lowered even neglecting the weak lensing data) we find that the significance of the $H_0$ tension only reduces to about $3.5\sigma$, while that of the $S_8$ tension falls below the $2\sigma$ level. Also, the statistical analysis we perform strongly favors $\mathrm{\Lambda }\mathrm{CDM}$ in all considered cases. Overall, we conclude that the specific multi-interacting dark energy model considered here, despite its broad generality and very rich cosmological phenomenology, cannot successfully restore the aforementioned overall concordance between early- and late-time observations.