In this paper we define a natural generalization of the von Neumann entropy to multiple parties that is symmetric with respect to all the parties. We call this measure multi-entropy. We show that for conformal field theories with holographic duals, the multi-entropy is computed by the area of an appropriate “soap-film” anchored on the boundary. We conjecture the quantum version of this prescription that takes into account the subleading corrections in $G_N$.

Spherical harmonic modes of gravitational waveforms for inspiraling compact binaries in eccentric orbits from post-Newtonian (PN) theory accurate to third post-Newtonian order and those extracted from numerical relativity (NR) simulations for binary black holes (BBHs) are compared. We combine results from the two approaches (PN and NR) to construct time-domain hybrid waveforms that describe the complete evolution of BBH mergers through inspiral-merger-ringdown (IMR) stages. These hybrids are then used in constructing a fully analytical dominant mode ($\ell =2$, $|m|=2$) eccentric IMR model. A simple extension to a multimode model based on this dominant mode model is also presented. Overlaps with quasicircular IMR waveform models including the effect of higher modes, maximized over a time and phase shift, hint at the importance ($\mathrm{mismatches}>1\%$) of including eccentricity in gravitational waveforms when analyzing BBHs lighter than $\sim 80M_{\odot }$, irrespective of the binary’s eccentricity (as it enters the LIGO bands) or mass ratio. Combined impact of eccentricity and higher modes seems to become more apparent through smaller overlaps with increasing inclination angles and mass ratios. Additionally, we show that the state-of-the-art quasicircular models including the effect of higher modes will not be adequate in extracting source properties for signals with initial eccentricities $e_0\gtrsim 0.1$.

We investigate some aspects of the ($2+1$)-dimensional Gauss-Bonnet black hole proposed in Hennigar et al. [Phys. Lett. B 808, 135657 (2020); Classical Quantum Gravity 38, 03LT01 (2021)]. The perturbations of scalar and massless spinorial fields are studied suggesting the dynamical stability of the geometry. The field evolution is analyzed calculating the quasinormal modes for different parameters and exploring the influence of the coupling constant of the theory. The hydrodynamical modes are also obtained in the small coupling limit. Furthermore, the entropy bound and the dominant semiclassical correction to the black hole entropy are calculated.

We analyze the geometry of a spherically symmetric black hole with an inner and outer apparent horizon that is perturbed by spherical null shells of matter. On a classical level we observe that the mass inflation instability is triggered, resulting in a growth of curvature and an inward displacement of the inner horizon. We study in detail the inner structure of the mass-inflated region and compare it with previous results obtained for the case in which the perturbing matter content has a continuous distribution. We then perform an approximate calculation of the renormalized stress-energy tensor of a quantum field in the vicinity of the inner horizon, and analyze the semiclassical backreaction on this region of the geometry. We find that the classical tendency for this horizon to move inward due to mass inflation is challenged and potentially overcome by a semiclassical tendency for it to inflate outward.

The local thermodynamic stability of a black hole (BH) in the canonical ensemble is defined by the positivity of the specific heat at constant global charges. Schwarzschild BHs in thermodynamic equilibrium with an energy reservoir are always unstable against small fluctuations of energy, whereas sufficiently near-extremal Reissner-Nordström/Kerr BHs are stable. One could expect that asymptotically flat hairy BHs branching off from such stable phases would also be, by continuity, locally thermodynamically stable for vanishingly little hair. We show this is not the case in some models, including scalarized BHs bifurcating from Reissner-Nordström and spinning BHs with synchronized hair bifurcating from Kerr. Specifically, it is found that quasibald BHs are locally thermodynamically unstable in the canonical ensemble for all global charges and regardless of being dynamically and entropically preferred over bald ones at fixed global charges.

We show that the quasinormal spectrum of gravitational perturbations of Schwarzschild–de Sitter black holes contains a new branch of purely imaginary modes. These modes are not algebraically special and we showed that the sum of them form the well-known in the literature exponential asymptotic tail. When the ratio of the event horizon radius to the cosmological horizon vanishes, these quasinormal modes approach modes of empty de Sitter spacetime. Thus, the spectrum consists of the two branches: Schwarzschild branch deformed by the cosmological constant and de Sitter branch deformed by the black hole mass. While the de Sitter branch contains purely imaginary modes only, the oscillatory modes (with nonzero real part) of the Schwarzschild branch can also become purely imaginary for some values of the cosmological constant, for which they approach the algebraically special mode.

We have studied the stability of wormhole geometries, under massless scalar, electromagnetic, and axial gravitational perturbations, in the context of higher dimensional spacetimes. Intriguingly, the construction of a wormhole spacetime in the presence of higher dimensions, known as braneworld wormholes, does not require the existence of exotic matter fields, unlike the scenario in four spacetime dimensions. Being a nonvacuum spacetime, the effective potential experienced by the axial gravitational perturbation differs considerably from the scenarios involving black holes. In particular, the present work provides one of the first attempts to study the gravitational perturbations of the wormhole spacetimes. Our analysis, involving both analytical and numerical techniques, demonstrates that there are echoes in the time domain signal of all the perturbations and the echo time delay is intimately related to the parameters originating from higher dimensions. Thereby combining the attempt to search for wormholes and extra dimensions, with the existence of gravitational wave echoes. Implications and future directions have also been discussed.

Current matched-filter searches for gravitational waves from binary black-hole mergers compare the calibrated detector data to waveform templates that omit the higher-order mode content of the signals predicted by general relativity. However, higher-order emission modes become important for highly inclined asymmetric sources with masses above $\simeq 100M_{\odot }$, causing current searches to be ill suited at detecting them. We present a new gravitational-wave search that implements templates including higher-order modes, adapted signal-glitch discriminators and trigger-ranking statistics to specifically target signals displaying strong higher modes, corresponding to nearly edge-on sources with total redshifted masses in the intermediate-mass black-hole range $M_T(1+z)\in (100,500)M_{\odot }$ and mass ratios $q\in (1,10)$. Our search shows a volumetric sensitivity gain of up to 450% to these signals compared to existing searches omitting higher-order modes. We deploy our search on public data from the third observing run of Advanced LIGO. While we find no statistically significant candidates beyond those already reported elsewhere, our search sets the stage to search for higher-mode rich signals in future observing runs. The efficient detection of such signals is crucial to performing detailed tests of general relativity, observing strong-field phenomena, and maximizing the chances of observing the yet uncharted realm of intermediate-mass black hole binaries.

Among the various oscillation modes of neutron stars, $f$- and $g$- modes are the most likely to be ultimately observed in binary neutron star mergers due to their relatively large coupling and shared frequencies with tidal excitations. The $f$-mode frequency and damping time are known to correlate in normal neutron stars with their compactness, and previous fits to hadronic stars are extended and shown to be valid for an extremely broad sampling of equations of state using a piecewise polytropic parametrization scheme for hadrons and a constant sound-speed parametrization for quark matter. Separate fits applicable to quark (self-bound) stars are improved. Much more significant correlations exist with tidal deformability, and therefore with moment of inertia and quadrupole moment. It is conclusively demonstrated that these correlations are the same for all types of stars, whether hadronic, hybrid, or pure quark, and its accuracy is quantified. A novel 1-node branch of the $f$-mode that occurs in low-mass hybrid stars in a narrow mass range just beyond the critical mass necessary for a phase transition to appear is identified. This 1-node branch shows the largest, but still small, deviations from the universal correlation for any configuration. It is characterized by a nonmonotonic relation between neutron star mass and $f$-mode frequency, in contrast to the behavior otherwise observed in normal, quark and hybrid stars. The $g$-mode only exists in matter with a nonbarotropic equation of state involving temperature, chemical potential or composition (such as being out of beta equilibrium), or a phase transition in barotropic matter. The $g$-mode therefore could serve as a probe for studying phase transitions in hybrid stars. In contrast with the $f$-mode, $g$-mode frequencies do not correlate well with tidal deformability, but depend strongly on properties of the transition (the density and the magnitude of the discontinuity) at the transition. Imposing causality and maximum mass constraints, a fit involving neutron star and phase transition properties is found and the $g$-mode frequency is determined to have an upper bound of about 1.25 kHz. However, if the sound speed $c_s$ in the inner core at densities above the phase transition density is restricted to $c_s^2\le 1/3$, $g$-mode frequencies can only reach about 0.8 kHz, which are significantly lower than $f$-mode frequencies (1.3–2.8 kHz). $g$-mode gravitational wave damping times are found to be extremely long, $>{10}^4\mathrm{s}$ (${10}^2\mathrm{s}$) in the inner core with $c_s^2\le 1/3$ (1), in comparison with $f$-mode damping times (0.1–1 s).

We study properties of Abrikosov-Nielsen-Olesen (ANO) strings with the Coleman-Weinberg (CW) potential, which we call CW-ANO strings. While the scale-invariant scalar potential has a topologically trivial vacuum admitting no strings at the classical level, quantum correction allows topologically nontrivial vacua and stable string solutions. We find that the system of the CW potential exhibits significant difference from that of the conventional Abelian-Higgs model with the quadratic-quartic potential. While a single-winding string is qualitatively similar in both systems, and the static intervortex force between two strings at large distance is attractive/repulsive in the type-I/II regime for both, that between two CW-ANO strings exhibits a nontrivial structure. It develops an energy barrier between them at intermediate distance, implying that the string with winding number $n>1$ can constitute a metastable bound state even in the type-II regime. We name such a superconductor type-$\overline{1.5}$. We also discuss implications to high-energy physics and cosmology.

This article summarizes the state of the art of ${\nu }_{\mu }$ and ${\overline{\nu }}_{\mu }$ $\mathrm{CC}0\pi$ cross-section measurements on carbon and argon and discusses the relevant nuclear models, parametrizations and uncertainties in GENIE v3. The $\mathrm{CC}0\pi$ event topology is common in experiments at a few-GeV energy range. Although its main contribution comes from quasielastic interactions, this topology is still not well understood. The GENIE global analysis framework is exploited to analyze $\mathrm{CC}0\pi$ datasets from MiniBooNE, T2K and $\mathrm{MINER}\nu \mathrm{A}$. A partial tune for each experiment is performed, providing a common base for the discussion of tensions between datasets. The results offer an improved description of nuclear $\mathrm{CC}0\pi$ datasets as well as data-driven uncertainties for each experiment. This work is a step towards a GENIE global tune that improves our understanding of neutrino interactions on nuclei. It follows from earlier GENIE work on the analysis of neutrino scattering datasets on hydrogen and deuterium.

We use the gravitoelectromagnetic approach to the solutions of Einstein’s equations in the weak-field and slow-motion approximation to investigate the impact of general relativity on galactic dynamics. In particular, we focus on a particular class of the solutions for the gravitomagnetic field, and show that, contrary to what is expected, they may introduce non-negligible corrections to the Newtonian velocity profile. The origin and the interpretation of these corrections are discussed and explicit applications to some galactic models are provided. These are the homogeneous solutions for the gravitomagnetic field, i.e., solutions with vanishing matter currents.

Hořava-Lifshitz gravity is an alternative theory to general relativity which breaks Lorentz invariance in order to achieve an ultraviolet complete and power-counting renormalizable theory of gravity. In the low-energy limit, Hořava-Lifshitz gravity coincides with a vector-tensor theory known as khronometric gravity. The deviation of khronometric gravity from general relativity can be parametrized by three coupling constants: $\alpha$, $\beta$, and $\lambda$. Solar system experiments and gravitational wave observations impose stringent bounds on $\alpha$ and $\beta$, while $\lambda$ is still relatively unconstrained ($\lambda \lesssim 0.01$). In this paper, we study whether one can constrain this remaining parameter with neutron star observations through the universal I-Love-Q relations between the moment of inertia (I), the tidal Love number (Love), and the quadrupole moment (Q), which are insensitive to details in the nuclear matter equation of state. To do so, we perturbatively construct slowly-rotating and weakly tidally-deformed neutron stars in khronometric gravity. We find that the I-Love-Q relations are independent of $\lambda$ in the limit $(\alpha ,\beta )\to 0$. Although some components of the field equations depend on $\lambda$, we show through induction and a post-Minkowskian analysis that slowly-rotating neutron stars do not depend on $\lambda$ at all. Tidally deformed neutron stars, on the other hand, are modified in khronometric gravity (though the usual Love number is not modified, as mentioned earlier), and there are potentially new, non-GR Love numbers, though their observability is unclear. These findings indicate that it may be difficult to constrain $\lambda$ with rotating/tidally-deformed neutron stars.

In the present paper we derive strong constrains on scalarization in scalar-Gauss-Bonnet (SGB) gravity using observations of pulsars in close binary systems. Since scalarized neutron stars carry a nonzero scalar change, they emit scalar dipole radiation while inspiraling which speeds up the orbital decay. The observations support the conjecture that such radiation is either absent or very small for the observed binary pulsars. Using this, we determine the allowed range of parameters for SGB gravity. We also transfer the derived constraints to black holes in SGB gravity. It turns out that the maximum mass of a scalarized black hole cannot exceed roughly 10 to 20 solar masses, depending on the initial assumptions we make for the nuclear matter equations of state. The black hole scalar charge on the other hand can reach relatively large values that are potentially observable.

The main aim of this paper is to provide cosmological constraints on the multiscalar field dark matter model, in which we assume the dark matter is made up of different ultralight scalar fields. As a first approximation, we consider they are real and do not interact with each other. We study the equations for both the background and perturbations for $N$-fields and present the evolution of the density parameters, the mass power spectrum, and the cosmic microwave background spectrum. In particular, we focus on two scalar fields with several combinations for the potentials $V(\varphi )=1/2m_{\varphi }^2{\varphi }^2$, $V(\varphi )=m_{\varphi }^2{f}^2[1+\cos (\varphi /f)]$, and $V(\varphi )=m_{\varphi }^2{f}^2[\cosh (\varphi /f)-1]$, however, the work, along with the code, could be easily extended to more fields. We use the data from baryon acoustic oscillation, big bang nucleosynthesis, Lyman-$\alpha$ forest, and supernovae to find constraints on the sampling parameters for the cases of a single field and double field, along with the Bayesian evidence. We found that some combinations of the potentials get penalized through the evidence, however, for others there is a preference as good as for the cold dark matter.

Inference of the equation of state (EOS) of dense nuclear matter in neutron-star cores is a principal science goal of x-ray and gravitational-wave observations of neutron stars. In particular, gravitational-wave observations provide an independent probe of the properties of bulk matter in neutron star cores that can then be used to compare with theoretically derived equations of state. In this paper, we quantify the systematic errors arising from the application of EOS-independent quasiuniversal relations in the estimation of neutron star tidal deformabilities and radii from gravitational-wave measurements and introduce a strategy to correct for the systematic biases in the inferred radii. We apply this method to a simulated population of events expected to be observed by future upgrades of current detectors and the next generation of ground-based observatories. We show that our approach can accurately correct for the systematic biases arising from approximate universal relations in the mass-radius curves of neutron stars. Using the posterior distributions of the mass and radius for the simulated population we infer the underlying EOS with a good degree of precision. Our method revives the possibility of using the universal relations for rapid Bayesian model selection of the dense matter EOS in gravitational-wave observations.

The most sensitive search pipelines for gravitational waves from compact binary mergers use matched filters to extract signals from the noisy data stream coming from gravitational wave detectors. Matched-filter searches require banks of template waveforms covering the physical parameter space of the binary system. Unfortunately, template bank construction can be a time-consuming task. Here we present a new method for efficiently generating template banks that utilizes automatic differentiation to calculate the parameter space metric. Principally, we demonstrate that automatic differentiation enables accurate computation of the metric for waveforms currently used in search pipelines, whilst being computationally cheap. Additionally, by combining random template placement and a Monte Carlo method for evaluating the fraction of the parameter space that is currently covered, we show that search-ready template banks for frequency-domain waveforms can be rapidly generated. Finally, we argue that differentiable waveforms offer a pathway to accelerating stochastic placement algorithms. We implement all our methods into an easy-to-use python package based on the jax framework, diffbank, to allow the community to easily take advantage of differentiable waveforms for future searches.

We investigate in detail the stimulated photon emission in pulse-shaped Laguerre-Gauss beams of arbitrary mode decomposition within the framework of Euler-Heisenberg effective theory. We elaborate on the analytic structure of the photon emission amplitude and identify its dominant and subdominant parts by analyzing each signature’s phase scaling. We identify three distinct nonlinear signatures: the orbital angular momentum flip ($\ell :1\to -1$), higher harmonic generation ($\ell :1\to 2$), and harmonic reduction ($\ell :1\to 0$). We estimate the signal photon yield for each signature under various pulse collision scenarios we explain in detail. We also outline a prospective experimental setup that may probe these signatures.

An extension of the Standard Model with anomaly free $U(1{)}_F$ flavor symmetry is studied in this paper. With this extension and the addition of the right-handed neutrino states, the solution of anomaly free charge assignments is found, which gives appealing texture zero and hierarchical Yukawa matrices. This gives us a natural understanding of the hierarchies between charged fermion masses and Cabibbo-Kobayashi-Maskawa matrix elements. Neutrino Dirac and Majorana coupling matrices also have desirable structures leading to successful neutrino oscillations with inverted neutrino mass ordering. Other interesting implications of the presented scenario are also discussed.

The presence of any extra radiation energy density at the time of cosmic microwave background formation can significantly impact the measurement of the effective relativistic neutrino degrees of freedom or $\mathrm{\Delta }{\mathrm{N}}_{\mathrm{eff}}$, which is very precisely measured by the Planck Collaboration. Here, we propose a scenario where a long-lived inert scalar, which is very weakly coupled to the dark sector, decays to a fermion dark matter via a “freeze-in” mechanism plus standard model neutrinos at very low temperature $(T<T_{\mathrm{BBN}})$. We explore this model in the fast expanding Universe, where it is assumed that the early epoch $(T>T_{\mathrm{BBN}})$ of the Universe is dominated by a nonstandard species $\mathrm{\Phi }$ instead of the standard radiation. In this nonstandard cosmological picture, such late-time decay of the inert scalar can inject some entropy to the neutrino sector after it decouples from the thermal bath and this will make substantial contribution to $\mathrm{\Delta }{\mathrm{N}}_{\mathrm{eff}}$. Additionally, in this scenario, the new contribution to $\mathrm{\Delta }{\mathrm{N}}_{\mathrm{eff}}$ is highly correlated with the dark matter sector. Thus, one can explore such feebly interacting dark matter particles by the precise measurement of $\mathrm{\Delta }{\mathrm{N}}_{\mathrm{eff}}$ using the current (Planck 2018) and forthcoming (CMB-S4 and SPT3G) experiments.