In the Comment written by Krasnikov on our recent paper, the author argues that a spherically symmetric perturbation coming from a massive object located on the other side of the wormhole would just add up to the total mass of the central object, and is therefore useless as an indicator of the wormhole presence. We point out that our Eq. (37) represents an acceleration variation in the motion of the star S2 due to an elliptic (and thus nonspherically symmetric) orbit of the star on the other side perturbing the metric. This time-dependent acceleration variation is in principle distinguishable from the original acceleration coming from the central object. We also point out that the author is trying to apply Birkhoff’s theorem in a setup where it cannot be applied in a straightforward way.

In their recent paper Dai and Stojkovic discuss an interesting possibility: a star near a wormhole mouth may gravitationally feel an object located near the other mouth. This means that a star’s trajectory may tell an observer that the star orbits a wormhole mouth and not a black hole. I argue that within the approximation used in the paper the effect is, in fact, unobservable irrespective of how accurate the measurements are.

Thermal states in some quantum field theories (QFTs) correspond to black holes in asymptotically AdS spacetime in the $\mathrm{AdS}/\mathrm{CFT}$ correspondence. We propose a direct procedure to construct holographic images of the black hole in the bulk from a given response function of the QFT on the boundary. The response function with respect to an external source corresponds to the asymptotic data of the bulk field generated by the source on the AdS boundary. According to the wave optics, we can obtain the images from the bulk field propagating in the bulk spacetime. For a thermal state on two-dimensional sphere dual to Schwarzschild-${\mathrm{AdS}}_4$ black hole, we demonstrate that the holographic images gravitationally lensed by the black hole can be constructed from the response function. In particular, the Einstein rings on the image can be clearly observed and their radius depends on the total energy of the QFT thermal state. These results are consistent with the size of the photon sphere of the black hole calculated in geometrical optics. This implies that, if there exists a dual gravitational picture for a given quantum system, we would be able to probe existence of the dual black hole by the Einstein rings constructed from observables of the quantum system.

The complex Sachdev-Ye-Kitaev (cSYK) model is a charge-conserving model of randomly interacting fermions. The interaction term can be chosen such that the model exhibits chiral symmetry. Then, depending on the charge sector and the number of interacting fermions, level spacing statistics suggests a fourfold categorization of the model into the three Wigner-Dyson symmetry classes. In this work, inspired by previous findings for the Majorana Sachdev-Ye-Kitaev model, we embed the symmetry classes of the cSYK model in the Altland-Zirnbauer framework and identify consequences of chiral symmetry originating from correlations across different charge sectors. In particular, we show that for an odd number of fermions, the model hosts exact many-body zero modes that can be combined into a generalized fermion that does not affect the system’s energy. This fermion directly leads to quantum-mechanical supersymmetry that, unlike explicitly supersymmetric cSYK constructions, does not require fine-tuned couplings, but only chiral symmetry. Signatures of the generalized fermion, and thus supersymmetry, include the long-time plateau in time-dependent correlation functions of fermion-parity-odd observables: The plateau may take nonzero value only for certain combinations of the fermion structure of the observable and the system’s symmetry class. We illustrate our findings through exact diagonalization simulations of the system’s dynamics.

An equivalence is demonstrated, by an explicit first order quantum calculation, between the Minkowski photon emission rate in the inertial frame for an accelerating charge moving on a Rindler trajectory with additional transverse drift motion and the combined Rindler photon emission and absorption rate of the same charge in the Rindler frame in the presence of the Davies-Unruh thermal bath. The equivalence also extends, for the Bremsstrahlung emitted by the same charge as calculated using the machinery of classical electrodynamics. The equivalence is shown to also hold for the case of accelerating charges moving on a Rindler trajectory with additional arbitrary transverse motion. Our results generalize those of Higuchi et al. (1992) and of Cozzella et al. (2017) for accelerated trajectories with circular transverse motion. Related issues and experimental implications are discussed.

We show that the topological degree of a Skyrmion field is the same as the Hopf charge of the field under the Hopf map and thus equals the linking number of the preimages of two points on the 2-sphere under the Hopf map. We further interpret two particular points on the 2-sphere as vortex zeros and the linking of these zero lines follows from the latter theorem. Finally we conjecture that the topological degree of the Skyrmion can be interpreted as the product of winding numbers of vortices corresponding to the zero lines, summing over clusters of vortices.

Within the superfield formalism, we calculate the two-point functions and the effective potential for the mass-deformed $\mathcal{N}=3$ Chern-Simons-matter theory and discuss the related renormalization group issues.

We provide a simple method to compute the energy in higher curvature gravity in asymptotically AdS spacetimes in even dimensions. It follows from the combined use of topological terms added to the gravity action, and the Wald charges derived from the augmented action functional. No additional boundary terms are needed. As a consistency check, we show that the formula for the conserved quantities derived in this way yields the correct result for the mass of asymptotically AdS black holes.

Considering a canonical ensemble, in which the temperature and charge on a wall of the cavity are fixed, we investigate the thermodynamics of a $D$-dimensional Gauss-Bonnet black hole in a finite spherical cavity. Moreover, we show that the first law of thermodynamics is still satisfied. We then discuss the phase structure and transition in both five and six dimensions. Specifically, we show that there always exist two regions in the parameter space. In one region, the system possesses one single phase. However, in the other region three phases could coexist and a van der Waals–like phase transition occurs. Finally, we find that there is a fairly close resemblance between the thermodynamic properties and phase structure of a Gauss-Bonnet-Maxwell black hole in a cavity and those in anti–de Sitter space.

Gravitational wave observations of the ringdown of the remnant black hole in a binary black hole coalescence provide a unique opportunity of confronting the black hole no-hair theorem in general relativity with observational data. The most robust tests are possible if multiple ringdown modes can be observed. In this paper, using state-of-the-art Bayesian inference methods and the most up-to-date knowledge of binary black hole population parameters and ringdown mode amplitudes, we evaluate the prospects for black hole spectroscopy with current and future ground based gravitational wave detectors over the next 10 years. For different population models, we estimate the likely number of events for which the subdominant mode can be detected and distinguished from the dominant mode. We show that black hole spectroscopy could significantly test general relativity for events seen by the proposed LIGO Voyager detectors.

In this paper we consider two different nonlinear $\sigma$-models minimally coupled to Eddington-inspired Born-Infeld gravity. We show that the resultant geometries represent minimal modifications with respect to those found in GR, though with important physical consequences. In particular, wormhole structures always arise, though this does not guarantee by itself the geodesic completeness of those space-times. In one of the models, quadratic in the canonical kinetic term, we identify a subset of solutions which are regular everywhere and are geodesically complete. We discuss characteristic features of these solutions and their dependence on the relationship between mass and global charge.

It is widely believed that electroweak baryogenesis should be suppressed in strong phase transitions with fast-moving bubble walls, but this effect has never been quantitatively studied. We rederive fluid equations describing transport of particle asymmetries near the bubble wall without making the small-wall-velocity approximation. We show that the suppression of the baryon asymmetry is a smooth function of the wall speed and that there is no special behavior when crossing the sound speed barrier. Electroweak baryogenesis can thus be efficient also with strong detonations, generically associated with models with observably large gravitational waves. We also make a systematic and critical comparison of our improved transport equations to another one commonly used in the literature, based on the vacuum expectation value (VEV)-insertion formalism.

Gravitational wave (GW) constraints have recently been used to significantly restrict models of dark energy and modified gravity. New bounds arising from GW decay and GW-induced dark energy instabilities are particularly powerful in this context, complementing bounds from the observed speed of GWs. We discuss the associated linear cosmology for Horndeski gravity models surviving these combined bounds and compute the corresponding cosmological parameter constraints, using cosmic microwave background, redshift space distortion, matter power spectrum, and baryon acoustic oscillation measurements from the Planck, Sloan Digital Sky Survey/Baryon Oscillation Spectroscopic Survey and 6dF surveys. The surviving theories are strongly constrained, tightening previous bounds on cosmological deviations from $\mathrm{\Lambda }\mathrm{CDM}$ by over an order of magnitude. We also comment on general cosmological stability constraints and the nature of screening for the surviving theories, pointing out that a raised strong coupling scale can ensure compatibility with gravitational wave constraints, while maintaining a functional Vainshtein screening mechanism on Solar System scales. Finally, we discuss the quasistatic limit as well as (constraints on) related observables for near-future surveys.

We present a detailed investigation of a subdominant oscillating scalar field [“early dark energy” (EDE)] in the context of resolving the Hubble tension. Consistent with earlier work, but without relying on fluid approximations, we find that a scalar field frozen due to Hubble friction until ${\log }_{10}(z_c)\sim 3.5$, reaching ${\rho }_{\mathrm{EDE}}(z_c)/{\rho }_{\mathrm{tot}}\sim 10\%$ and diluting faster than matter afterwards, can bring cosmic microwave background (CMB), baryonic acoustic oscillations, supernovae luminosity distances, and the late-time estimate of the Hubble constant from the SH0ES Collaboration into agreement. A scalar field potential that scales as $V(\varphi )\propto {\varphi }^{2n}$ with $2\lesssim n\lesssim 3.4$ around the minimum is preferred at the 68% confidence level, and the Planck polarization places additional constraints on the dynamics of perturbations in the scalar field. In particular, the data prefer a potential that flattens at large field displacements. A Markov-chain Monte Carlo analysis of mock data shows that the next-generation CMB observations (i.e., CMB-S4) can unambiguously detect the presence of the EDE at a very high significance. This projected sensitivity to the EDE dynamics is mainly driven by improved measurements of the $E$-mode polarization. We also explore new observational signatures of EDE scalar field dynamics: (i) We find that depending on the strength of the tensor-to-scalar ratio, the presence of the EDE might imply the existence of isocurvature perturbations in the CMB. (ii) We show that a strikingly rapid, scale-dependent growth of EDE field perturbations can result from parametric resonance driven by the anharmonic oscillating field for $n\approx 2$. This instability and ensuing potentially nonlinear, spatially inhomogeneous, dynamics may provide unique signatures of this scenario.

We propose a mechanism borrowed from string theory which yields a nonsingular transition from a phase of ekpyrotic contraction to the expanding phase of standard big bang cosmology. The same mechanism converts the initial vacuum spectrum of cosmological fluctuations before the bounce into a scale-invariant one, and also changes the spectrum of gravitational waves into an almost scale-invariant one. The scalar and tensor tilts are predicted to be the same, in contrast to the predictions from the “string gas cosmology” scenario. The amplitude of the gravitational wave spectrum depends on the ratio of the string scale to the Planck scale and may be in reach of upcoming experiments.

The $E_G$ statistic is a powerful probe for detecting deviations from general relativity by combining weak lensing (WL), real-space clustering, and redshift space distortion (RSD) measurements, thus probing both the lensing and the growth effective Newton constants ($G_L$ and $G_{\mathrm{eff}}$). We construct an up-to-date compilation of $E_G$ statistic data including both redshift and scale dependence [$E_G(R,z)$]. We combine this $E_G$ data compilation with an up-to-date compilation of $f{\sigma }_8$ data from RSD observations to identify the current level of tension between the Planck-$\mathrm{\Lambda }\mathrm{CDM}$ standard model based on general relativity and a general model-independent redshift evolution parametrization of $G_L$ and $G_{\mathrm{eff}}$. Each $f{\sigma }_8$ data point considered has been published separately in the context of independent analyses of distinct galaxy samples. However, there are correlations among the data points considered due to overlap of the analyzed galaxy samples. Due to these correlations, the derived levels of tension of the best-fit parameters with Planck-$\mathrm{\Lambda }\mathrm{CDM}$ are somewhat overestimated, but this is the price to pay for maximizing the information encoded in the compilation considered. We find that the level of tension increases from about $3.5\sigma$ for the $f{\sigma }_8$ data compilation alone to about $6\sigma$ when the $E_G$ data are also included in the analysis. The direction of the tension is the same as implied by the $f{\sigma }_8$ RSD growth data alone [lower ${\mathrm{\Omega }}_m$ and/or weaker effective Newton constant at low redshifts for both the lensing and the growth effective Newton constants ($G_L$ and $G_{\mathrm{eff}}$)]. These results further amplify the hints for weakening modified gravity discussed in other recent analyses.

In this work, we use the equation of state (EOS) of the ($2+1$)-flavor Nambu-Jona-Lasinio (NJL) model to study the structure of the strange quark star. With a new free parameter $\alpha$, the Lagrangian is constructed by two parts, the original NJL Lagrangian and the Fierz transformation of it, as $\mathcal{L}=(1-\alpha ){\mathcal{L}}_{\mathrm{NJL}}+\alpha {\mathcal{L}}_{\text{Fierz}}$. To determine the range of $\alpha$, we compare the binding energies in the two-flavor and ($2+1$)-flavor cases. We also consider the constraints of chemical equilibrium and electric charge neutrality in the strange quark star and choose six representative EOSs with different $\alpha$ and $B$ (bag constant) to study their influence on the structure of the strange quark star. As a result, we find that a larger $\alpha$ and a smaller $B$ correspond to a heavier star with a stiffer EOS. Furthermore, the heaviest strange quark star is in agreement with not only the recent mass observation of PSR $\mathrm{J}0740+6620$ and the x-ray observations on radius measurements, but also the constraint on the tidal deformability of GW170817.

We compute the mass, radius and tidal deformability of stars containing phase transitions from hadronic to quark phase(s). These quantities are computed for three types of hadronic envelopes: purely nuclear, hyperonic, and $\mathrm{\Delta }$-resonance–hyperon admixed matter. We consider either a single first-order phase transition to a quark phase with a maximally stiff equation of state (EOS) or two sequential first-order phase transitions mimicking a transition from hadronic (H) to a quark matter phase followed by a second phase transition to another quark phase. Such a construct emulates the results of the computations of the EOS, which include two-flavor color-superconducting and color-flavor-locked superconducting phases at low and high density. We explore the parameter space which produces low-mass twin and triplet configurations where equal-mass stars have substantially different radii and tidal deformabilities. We demonstrate that while for purely hadronic stiff EOS the obtained maximum mass is inconsistent with the upper limit on this quantity placed by GW170817, the inclusion of the hyperonic and $\mathrm{\Delta }$-resonance degrees of freedom, as well as the deconfinement phase transition at sufficiently low density, produces a configuration of stars consistent with this limit. The obtained hybrid star configurations are in the mass range relevant for the interpretation of the GW170817 event. We compare our results for the tidal deformability with the limits inferred from GW170817 showing that the onset of non-nucleonic phases, such as $\mathrm{\Delta }$-resonance–hyperon admixed phase and/or the quark phase(s), are favored by these data if the nuclear EOS is stiff. Also, we show that low-mass twins and especially triplets proliferate the number of combinations of possible types of stars that can undergo a merger event, the maximal number being six in the case of triplets. The prospects for uncovering the first-order phase transition(s) to and in quark matter via measurements of tidal deformabilities in merger events are discussed.