Identifying an entanglement island requires exquisite control over the entropy of quantum fields, which is available only in toy models. Here we present a set of sufficient conditions that guarantee the existence of an island and place an upper bound on the entropy computed by the island rule. This is enough to derive the main features of the Page curve for an evaporating black hole in any spacetime dimension. Our argument makes use of Wall’s maximin formulation and the quantum focusing conjecture. As a corollary, we derive a novel entropy bound.

An exotic rotationally invariant harmonic oscillator (ERIHO) is constructed by applying a nonunitary isotropic conformal bridge transformation (CBT) to a free planar particle. It is described by the isotropic harmonic oscillator Hamiltonian supplemented by a Zeeman type term with a real coupling constant $g$. The model reveals the Euclidean ($|g|<1$) and Minkowskian ($|g|>1$) phases separated by the phases $g=+1$ and $g=-1$ of the Landau problem in the symmetric gauge with opposite orientation of the magnetic field. A hidden symmetry emerges in the system at rational values of $g$. Its generators, together with the Hamiltonian and angular momentum produce nonlinearly deformed $\mathfrak{u}(2)$ and $\mathfrak{g}\mathfrak{l}(2,\mathbb{R})$ algebras in the cases of $0<|g|<1$ and $\infty >|g|>1$, which transmute one into another under the inversion $g\to -1/g$. Similarly, the true, $\mathfrak{u}(2)$, and extended conformal, $\mathfrak{g}\mathfrak{l}(2,\mathbb{R})$, symmetries of the isotropic Euclidean oscillator ($g=0$) interchange their roles in the isotropic Minkowskian oscillator ($|g|=\infty$), while two copies of the $\mathfrak{g}\mathfrak{l}(2,\mathbb{R})$ algebra of analogous symmetries mutually transmute in Landau phases. We show that the ERIHO system is transformed by a peculiar unitary transformation into the anisotropic harmonic oscillator generated, in turn, by anisotropic CBT. The relationship between the ERIHO and the subcritical phases of the harmonically extended Landau problem, as well as with a plane isotropic harmonic oscillator in a uniformly rotating reference frame, is established.

We establish the large central charge behavior of the entanglement negativity for a mixed state configuration of a single interval enclosed between two intervals in a holographic ${\mathrm{CFT}}_{1+1}$. To this end we utilize the monodromy technique to elucidate the large central charge limit of a four point twist correlator which characterizes the negativity of the mixed state configuration. Subsequently we analyze the large central charge limit of the six point twist correlator which reduces to the above four point correlator in a specific limit. The results provide a strong consistency check for our recently proposed holographic entanglement negativity conjecture in the ${\mathrm{AdS}}_3/{\mathrm{CFT}}_2$ scenario.

The point-splitting renormalization method offers a prescription to calculate finite expectation values of quadratic operators constructed from quantum fields in a general curved spacetime. It has been recently shown by Levi and Ori that when the background metric possesses an isometry, like stationary or spherically symmetric black holes, the method can be upgraded into a pragmatic procedure of renormalization that produces efficient numerical calculations. In this paper we show that when the background enjoys three-dimensional spatial symmetries, like homogeneous expanding universes, the above pragmatic regularization technique reduces to the well-established adiabatic regularization method.

We construct the free Lagrangian of the magnetic sector of Carrollian electrodynamics. The construction relies on Helmholtz integrability condition for differential equations in a self-consistent algorithm, working hand in hand with imposing invariance under infinite dimensional Conformal Carroll algebra. It requires inclusion of new fields in the dynamics and the system is free of gauge redundancies. We next add interaction (quartic) terms to the free Lagrangian, strictly constrained by conformal invariance and Carrollian symmetry. The dynamical realization of the non-semi-simple infinite dimensional symmetry algebra at the level of charge algebra is exact and free from central terms.

The chameleon model was proposed as a promising candidate for the dark energy screening mechanism. It is not straightforward to detect the fifth force mediated by the chameleon scalar field in a high-density environment, such as those in a ground-based laboratory. Nevertheless, short-range gravitational experiments such as the torsion pendulum experiment can provide strong constraints on the chameleon model. In this work, we constrain the chameleon model from a precise test of the inverse-square law at Huazhong University of Science and Technology. In particular, we take full advantage of the regular flat-plate structure of the test and attraction mass, which gives rise to accurate modeling for the chameleon force and torque. The derived analytical results on the chameleon torque are shown to agree well with those by numerical calculations. Subsequently, based on the experimental data, the parameter space of the chameleon model is analyzed, and the results are presented in terms of a more stringent constraint on the model parameters.

All axisymmetric solutions to the near-horizon geometry equation with a cosmological constant defined on a topological 2-sphere were derived. The regularity conditions preventing cone singularity at the poles were accounted for. The one-to-one correspondence of the solutions with the extremal horizons in the Kerr–(anti–)de Sitter spacetimes was found. A solution corresponding to the triply degenerate horizon was identified and characterized. The solutions were also identified among the solutions to the Petrov type D equation.

We investigate the gravitational effect of large-scale radiation perturbations on small-scale structure formation. In addition to making the growth of matter perturbations scale dependent, the free streaming of radiation also affects the coupling between structure formation at small and large scales. We study this using separate universe $N$-body simulations to compute the (isotropized) squeezed limit matter bispectrum and the linear halo bias. Our results show that the scale dependence in the growth of long-wavelength matter perturbations, caused by radiation, translates into these quantities acquiring a nontrivial scale dependence at $k\lesssim 0.05{\mathrm{Mpc}}^{-1}$. In a universe with radiation composed of cosmic microwave background photons and three species of massless neutrinos, the bias of halos with $b=2$ at high $k$ will decrease by $0.29\%,0.45\%$, and 0.8% between $k=0.05{\mathrm{Mpc}}^{-1}$ and $k=0.0005{\mathrm{Mpc}}^{-1}$ at redshifts $z=0$, 1, and 3, respectively. For objects with $b\gg 1$, these differences approach $0.43\%,0.68\%$, and 1.2%, respectively.

The cross-correlation between the cosmic microwave background (CMB) fields and matter tracers carries important cosmological information. In this paper, we forecast by a signal-to-noise ratio analysis the information contained in the cross-correlation of the CMB anisotropy fields with source counts for future cosmological observations and its impact on cosmological parameters uncertainties, using a joint tomographic analysis. We include temperature, polarization, and lensing for the CMB fields and galaxy number counts for the matter tracers. We consider Planck-like, the Simons Observatory, LiteBIRD, and CMB-S4 specifications for CMB, and Euclid-like, Vera C. Rubin Observatory, SPHEREx, EMU, and SKA1 for future galaxy surveys. We restrict ourselves to quasilinear scales in order to deliver results that are free as much as possible from the uncertainties in modeling nonlinearities. We forecast by a Fisher matrix formalism the relative importance of the cross-correlation of source counts with the CMB in the constraints on the parameters for several cosmological models. We obtain that the CMB-number counts cross-correlation can improve the dark energy figure of merit (FOM) at most up to a factor $\sim 2$ for $\mathrm{LiteBIRD}+\mathrm{CMB}\text{−}\mathrm{S}4\times \mathrm{SKA}1$ compared to the uncorrelated combination of both probes and will enable the Euclid-like photometric survey to reach the highest FOM among those considered here. We also forecast how CMB-galaxy clustering cross-correlation could increase the FOM of the neutrino sector, also enabling a statistically significant ($\gtrsim 3\sigma$ for $\mathrm{LiteBIRD}+\mathrm{CMB}\text{−}\mathrm{S}4\times \mathrm{SPHERE}\mathrm{x}$) detection of the minimal neutrino mass allowed in a normal hierarchy by using quasilinear scales only. Analogously, we find that the uncertainty in the local primordial non-Gaussianity could be as low as $\sigma (f_{\mathrm{NL}})\sim 1.5–2$ by using two-point statistics only with the combination of CMB and radio surveys, such as EMU and SKA1. Further, we quantify how cross-correlation will help characterizing the galaxy bias. Our results highlight the additional constraining power of the cross-correlation between CMB and galaxy clustering from future surveys, which is mainly based on quasilinear scales and therefore, sufficiently robust to nonlinear effects.

We derive the nonrelativistic limit of a massive vector field. We show that the Cartesian spatial components of the vector behave as three identical, noninteracting scalar fields. We find classes of spherical, cylindrical, and planar self-gravitating vector solitons in the Newtonian limit. The gravitational properties of the lowest-energy vector solitons—the gravitational potential and density field—depend only on the net mass of the soliton and the vector particle mass. In particular, these self-gravitating, ground-state vector solitons are independent of the distribution of energy across the vector field components and are indistinguishable from their scalar-field counterparts. Fuzzy vector dark matter models can therefore give rise to halo cores with observational properties that are identical to the ones in scalar fuzzy dark matter models. We also provide novel hedgehog vector soliton solutions which cannot be observed in scalar-field theories. The gravitational binding of the lowest-energy hedgehog halo is about 3 times weaker than the ground-state vector soliton. Finally, we show that no spherically symmetric solitons exist with a divergence-free vector field.

We examine the constraints on sub-GeV dark sector particles set by the proto-neutron star cooling associated with the core-collapse supernova event SN1987a. Considering explicitly a dark photon portal dark sector model, we compute the relevant interaction rates of dark photon ($A^{\prime }$) and dark fermion ($\chi$) with the Standard Model particles as well as their self-interaction inside the dark sector. We find that even with a small dark sector fine structure constant ${\alpha }_D\ll 1$, dark sector self-interactions can easily lead to their own self-trapping. This effect strongly limits the energy luminosity carried away by dark sector particles from the supernova core and thus drastically affects the parameter space that can be constrained by SN1987a. We consider specifically two mass ratios $m_{A^{\prime }}=3m_{\chi }$ and $3m_{A^{\prime }}=m_{\chi }$ which represent scenarios where the decay of $A^{\prime }$ to $\chi \overline{\chi }$ is allowed or not. For $m_{A^{\prime }}=3m_{\chi }$, we show that this effect can completely evade the supernova bounds on widely examined dark photon parameter space for a dark sector with ${\alpha }_D\gtrsim {10}^{-7}$. In particular, for the mass range $m_{\chi }\lesssim 20\mathrm{MeV}$, supernova bounds can only be applied to weakly self-interacting dark sector with ${\alpha }_D\lesssim {10}^{-15}$. For $3m_{A^{\prime }}=m_{\chi }$, bounds in regions where ${\alpha }_D\gtrsim {10}^{-7}$ for $m_{\chi }\lesssim 20\mathrm{MeV}$ can be evaded similarly. Our findings thus imply that the existing supernova bounds on light dark particles can be generally eluded by a similar self-trapping mechanism. This also implies that nonstandard strongly self-interacting neutrino is not consistent with the SN1987a observation. Same effects can also take place for other known stellar bounds on dark sector particles.

Binary millisecond pulsars (MSPs) are detached systems consisting of a MSP and a He white dwarf. If the initial orbital periods of binary MSPs are shorter than 0.3 day, they would evolve toward ultracompact binary pulsars due to the rapid orbital shrinkage by the gravitational wave (GW) radiation. During the orbital decay, the MSP with an ellipticity would spin down due to GW radiation and magnetic dipole radiation. Our calculations indicate that the angular momentum loss is dominated by the GW radiation when the ellipticities of the neutron stars (NSs) are in the range of $(1–50)\times {10}^{-7}$, and the frequencies of high-frequency GW signals from the rotating NSs are 10–100 Hz when the binary pulsars can be visible as low-frequency GW sources. These high-frequency GW signals are possible to be detected by aLIGO and the third-generation GW detectors such as Einstein Telescope, depending on the frequencies and the distances. Therefore, ultracompact binary pulsars have an opportunity to become intriguing dual-line GW sources. By detecting low-frequency GW signals, the NS mass can be accurately derived. A dual-line detection of two band GW signals could provide a constraint on the moment of inertia and the ellipticity of the NS. Thus dual-line GW sources can be potentially applied to constrain the equation of state of NSs.

We study a sparse Sachdev-Ye-Kitaev (SYK) model with $N$ Majoranas where only $\sim kN$ independent matrix elements are nonzero. We identify a minimum $k\gtrsim 1$ for quantum chaos to occur by a level statistics analysis. The spectral density in this region, and for a larger $k$, is still given by the Schwarzian prediction of the dense SYK model, though with renormalized parameters. Similar results are obtained for a beyond linear scaling with $N$ of the number of nonzero matrix elements. This is a strong indication that this is the minimum connectivity for the sparse SYK model to still have a quantum gravity dual. We also find an intriguing exact relation between the leading correction to moments of the spectral density due to sparsity and the leading $1/d$ correction of Parisi’s U(1) lattice gauge theory in a $d$-dimensional hypercube. In the $k\to 1$ limit, different disorder realizations of the sparse SYK model show emergent random matrix statistics that for fixed $N$ can be in any universality class of the tenfold way. The agreement with random matrix statistics is restricted to short-range correlations, no more than a few level spacings, in particular in the tail of the spectrum. In addition, emergent discrete global symmetries in most of the disorder realizations for $k$ slightly below one give rise to $2^m$-fold degenerate spectra, with $m$ being a positive integer. For $k=3/4$, we observe a large number of such emergent global symmetries with a maximum $2^8$-fold degenerate spectra for $N=26$.

We calculate the four-point function of $1/2$-BPS (Bogomolnyi–Prasad–Sommerfield) determinant operators in $\mathcal{N}=4$ SYM (super Yang-Mills) at next-to-leading order at weak coupling. We use two complementary methods recently developed for a class of determinant three-point functions: one is based on Feynman diagrams and it extracts perturbative data at finite $N$, while the other one expresses a generic correlator of determinants as the zero-dimensional integral over an auxiliary matrix field. We generalize the latter approach to calculate one-loop corrections and we solve the four-point function in a semiclassical approach at large $N$. The results allow us to comment on the order of the phase transition that the four-point function is expected to exhibit in an exact integrability-based description.

The effect of energy absorption during the binary evolution of Exotic-compact-objects (ECOs) is extensively studied. We review the underlying mechanism that provides the energy dissipation in material objects—tidal friction. We show that unlike typical astrophysical objects, where absorption due to viscosity is negligible, in ECOs, absorption could potentially mimic the analogous effect of black-holes (BHs)—tidal heating. We stand for their differences and similarities in the context of energy dissipation during the inspiral. Inspired by the membrane paradigm and recent studies, we demonstrate how viscosity is a defining feature that quantifies how close is the ECO absorption to that of a classical BH absorption. We show that for ECOs, viscosity can induce significant modifications to the GW waveform, which in some favorable scenarios of supermassive binaries of equal mass and spin, enables the measurement of the ECO absorption in the future precision gravitational-wave (GW) observations. Finally, we discuss the implications on the ECO reflection coefficient and the relation to the universal viscosity to volume entropy bound.

Accurate parameter estimation is key to maximizing the scientific impact of gravitational-wave astronomy. Parameters of a binary merger are typically estimated using Bayesian inference. It is necessary to make several assumptions when doing so, one of which is that the detectors output stationary Gaussian noise. We test the validity of these assumptions by performing percentile-percentile tests in both simulated Gaussian noise and real detector data in the first observing run of Advanced LIGO (O1). We add simulated signals to 512s of data centered on each of the three events detected in O1—GW150914, GW151012, and GW151226—and check that the recovered credible intervals match statistical expectations. We find that we are able to recover unbiased parameter estimates in the real detector data, indicating that the assumption of Gaussian noise does not adversely effect parameter estimates. However, we also find that both the parallel-tempered sampler emcee_pt and the nested sampler dynesty struggle to produced unbiased parameter estimates for GW151226-like signals, even in simulated Gaussian noise. The emcee_pt sampler does produce unbiased estimates for GW150914-like signals. This highlights the importance of performing percentile-percentile tests in different targeted areas of parameter space.

Using the notion of thermodynamic length, the first law of thermodynamics is consistently derived for two binary configurations of equal Kerr-Newman black holes separated by a massless strut. As in the electrostatic systems of two Reissner-Nordström black holes and stationary vacuum systems of two Kerr black holes considered earlier, the thermodynamic length $\ell$ turns out to be defined by the same simple formula $\ell =L\exp ({\gamma }_0)$, $L$ being the coordinate length of the strut and ${\gamma }_0$ the value of the metric function $\gamma$ on the strut, which permits the elaboration of $\ell$ in a concise analytic form. The expression of the free energy in the case of two generic Kerr-Newman black holes is also proposed.

We investigate radial oscillations of pure neutron stars and hybrid stars, employing equations of state of nuclear matter from Brueckner-Hartree-Fock theory, and of quark matter from the Dyson-Schwinger quark model, performing a Gibbs construction for the mixed phase in hybrid stars. We calculate the eigenfrequencies and corresponding oscillation functions. Our results for the zero points of the first-order radial oscillation frequencies give the maximum mass of stable neutron stars, consistent with the common criterion $dM/d{\rho }_c=0$. Possible observations of the radial oscillation frequencies could help to learn more about the equation of state, predict the maximum mass of neutron stars more precisely, and indicate the presence of quark matter.

We adapt a method, originally developed for searches for quasimonochromatic, quasi-infinite duration gravitational-wave signals, to directly detect new light gauge bosons with laser interferometers, which could be candidates for dark matter. To search for these particles, we optimally choose the analysis coherence time as a function of boson mass, such that all of the signal power will be confined to one frequency bin. We focus on the dark photon, a gauge boson that could couple to the baryon or baryon-lepton number, and explain that its interactions with gravitational-wave interferometers result in a narrow-band, stochastic signal. We provide an end-to-end analysis scheme, estimate its computational cost, and investigate follow-up techniques to confirm or rule out dark matter candidates. Furthermore, we derive a theoretical estimate of the sensitivity, and show that it is consistent with both the empirical sensitivity determined through simulations, and results from a cross-correlation search. Finally, we place Feldman-Cousins upper limits using data from LIGO Livingston’s second observing run, which give a new and strong constraint on the coupling of gauge bosons to the interferometer.