The detection of nanoHertz gravitational waves through pulsar timing arrays hinges on identifying a common stochastic process affecting all pulsars in a correlated way across the sky. In the presence of other deterministic and stochastic processes affecting the time-of-arrival of pulses, a detection claim must be accompanied by a detailed assessment of the various physical or phenomenological models used to describe the data. In this study, we propose posterior predictive checks as a model-checking tool that relies on the predictive performance of the models with regards to new data. We derive and study predictive checks based on different components of the models, namely the Fourier coefficients of the stochastic process, the correlation pattern, and the timing residuals. We assess the ability of our checks to identify model misspecification in simulated datasets. We find that they can accurately flag a stochastic process spectral shape that deviates from the common power-law model as well as a stochastic process that does not display the expected angular correlation pattern. Posterior predictive likelihoods derived under different assumptions about the correlation pattern can further be used to establish detection significance. In the era of nanoHertz gravitational wave detection from different pulsar-timing datasets, such tests represent an essential tool in assessing data consistency and supporting astrophysical inference.

A gravitational-wave background can be detected in pulsar-timing-array data as Hellings-Downs correlations among the timing residuals measured for different pulsars. The optimal statistic implements this concept as a classical null-hypothesis statistical test: a null model with no correlations can be rejected if the observed value of the statistic is very unlikely under that model. To address the dependence of the statistic on the uncertain pulsar noise parameters, the pulsar-timing-array community has adopted a hybrid classical-Bayesian scheme [S. J. Vigeland et al., Phys. Rev. D 98, 044003 (2018).] in which the posterior distribution of the noise parameters induces a posterior distribution for the statistic. In this article we propose a rigorous interpretation of the hybrid scheme as an instance of posterior predictive checking, and we introduce a new summary statistic (the Bayesian signal-to-noise ratio) that should be used to accurately quantify the statistical significance of an observation instead of the mean posterior signal-to-noise ratio, which does not support such a direct interpretation. In addition to falsifying the no-correlation hypothesis, the Bayesian signal-to-noise ratio can also provide evidence supporting the presence of Hellings-Downs correlations. We demonstrate our proposal with simulated datasets based on NANOGrav’s 12.5-yr data release. We also establish a relation between the posterior distribution of the statistic and the Bayes factor in favor of correlations, thus calibrating the Bayes factor in terms of hypothesis-testing significance.

The emission of continuous gravitational waves (CWs), with duration much longer than the typical data taking runs, is expected from several sources, notably spinning neutron stars, asymmetric with respect to their rotation axis and more exotic sources, like ultralight scalar boson clouds formed around Kerr black holes and subsolar mass primordial binary black holes. Unless the signal time evolution is well predicted and its relevant parameters accurately known, the search for CWs is typically based on semicoherent methods, where the full dataset is divided into shorter chunks of given duration, which are properly processed and then incoherently combined. In this paper, we present a semicoherent method, in which the so-called “five-vector” statistics is computed for the various data segments and then summed after the removal of the Earth Doppler modulation and signal intrinsic spin-down. The method can work with segment duration of several days, thanks to a double-stage procedure in which an initial rough correction of the Doppler and spin-down is followed by a refined step in which the residual variations are removed. This method can be efficiently applied for directed searches, where the source position is known to a good level of accuracy, and in the candidate follow-up stage of wide-parameter space searches.

It is shown that energy, entropy and the first law of electrically charged black holes with scalar hair can be consistently described in a general Hamiltonian approach to black hole thermodynamics. In particular, we prove that the associated “hairy” Smarr formula is modified with respect to its standard form.

The Gibbons-Werner-Ono-Ishihara-Asada method for gravitational lensing in a stationary spacetime has recently been reexamined [Huang and Cao, arXiv:2306.04145], in which the gravitational deflection angle of light based on the Gauss-Bonnet theorem can be rewritten as a line integral of two functions $H$ and $T$. The present paper proves that the Huang-Cao line integral definition and the Ono-Ishihara-Asada one [Phys. Rev. D 96, 104037 (2017)] are equivalent to each other, whatever asymptotic regions are. A remark is also made concerning the direction of a light ray in a practical use of these definitions.

We reanalyze the far zone contribution to the two-body conservative dynamics arising from interaction between radiative and longitudinal modes, the latter sourced by mass and angular momentum, which in the mass case is known as tail process. We verify the expected correspondence between two loop self-energy amplitudes and the gluing of two classical (one leading order, one at one loop) emission amplitudes, with focus on the Ward identities. As part of our analysis, we originally compute emission and self-energy processes with the longitudinal mode sourced by angular momentum for generic electric and magnetic multipoles and we highlight the role of the contribution from source interaction with two gravitational fields.

Some stochastic gravitational wave background models from the early Universe has a cutoff frequency close to 100 MHz, due to the horizon of the inflationary phase. To detect gravitational waves at such frequencies, resonant electromagnetic cavities are very suitable. In this work, we study the expected frequency response of such detectors using a brand new approach, and show how we could use them to probe this cutoff frequency and also the energy density per frequency of this stochastic background. This paper paves the way for further experimental studies to probe the most ancient relic of the Universe.

We study a simple axionlike model with a charged scalar $\varphi$ and a double-charged scalar $\zeta$ of global $U(1)$ symmetry. A particular feature of our model is that a vacuum manifold is a torus knot. We consider a hierarchical symmetry-breaking scenario where $\zeta$ first condenses, giving rise to cosmic $\zeta$-strings, and the subsequent condensation of $\varphi$ leads to domain-wall formation spanning the $\zeta$-strings. We find that the formation of the walls undergoes two different regimes depending on the magnitude of an explicit breaking term of the relative $U(1)$ between $\zeta$ and $\varphi$. One is the weakly interacting regime where the walls are accompanied by another cosmic $\varphi$ strings. The other is the strongly interacting regime where no additional strings appear. In both regimes, neither a $\zeta$-string, a $\varphi$-string nor a wall alone is topological, but the composite of an appropriate number of strings and walls as a whole is topologically stable, characterized by the fundamental homotopy group of the torus knot. We confirm the formation and the structure of the string-wall system by first-principle cosmological two-dimensional simulations. We find stable string-wall composites at equilibrium, where the repulsive force between $\zeta$-strings and the tension of walls balances, and a novel reconnection of the string-wall composites.

We present a phenomenological model to investigate the chiral phase transition characterized by parity doubling in dense, beta equilibrated, cold matter. Our model incorporates effective interactions constrained by SU(3) relations and considers baryonic degrees of freedom. By constraining the model with astrophysical data and nuclear matter properties, we find a first-order phase transition within realistic values of the slope parameter L. The inclusion of the baryon octet and negative parity partners, along with a chiral-invariant mass $m_0$, allows for a chiral symmetric phase with massive hadrons. Through exploration of parameter space, we identify parameter sets satisfying mass and radius constraints without requiring a partonic phase. The appearance of the parity partner of the nucleon, the N(1535) resonance, suppresses strangeness, pushing hyperonization to higher densities. We observe a mild first-order phase transition to the chirally restored phase, governed by $m_0$. Our calculations of surface tension highlight its strong dependence on $m_0$. The existence of mixed phases is ruled out since they become energetically too costly. We compare stars with metastable and stable cores using both branches of the equation of state. Despite limited lifespans due to low surface tension values, phase conversion and star contraction could impact neutron stars with masses around 1.3 solar masses or more. We discuss some applications of this model in its nonzero temperatures generalization and scenarios beyond beta equilibrium that can provide insights into core-collapse supernovae, protoneutron star evolution, and neutron star mergers. Core-collapse supernovae dynamics, influenced by chiral symmetry restoration and exotic hadronic states, affect explosion mechanisms and nucleosynthesis.

We discuss in detail the possibility that the “type-II Majoron”—that is, the pseudo-Nambu-Goldstone boson that arises in the context of the type-II seesaw mechanism if the lepton number is spontaneously broken by an additional singlet scalar—account for the dark matter (DM) observed in the Universe. We study the requirements the model’s parameters have to fulfill in order to reproduce the measured DM relic abundance through two possible production mechanisms in the early Universe, freeze-in and misalignment, both during a standard radiation-dominated era and early matter domination. We then study possible signals of type-II Majoron DM and the present and expected constraints on the parameter space that can be obtained from cosmological observations, direct detection experiments, and present and future searches for decaying DM at neutrino telescopes and cosmic-ray experiments. We find that—depending on the Majoron mass, the production mechanism, and the vacuum expectation value of the type-II triplet—all of the three decay modes (photons, electrons, neutrinos) of Majoron DM particles can yield observable signals at future indirect searches for DM. Furthermore, in a corner of the parameter space, detection of Majoron DM is possible through electron recoil at running and future direct detection experiments.

In a two-component dark matter (DM) set up, when ${\mathrm{DM}}_1$ is in equilibrium with the thermal bath, the other ${\mathrm{DM}}_2$ can be equilibrated just by sizeable interaction with ${\mathrm{DM}}_1$, even without any connection with the visible-sector particles. We show that such DM candidates (${\mathrm{DM}}_2$) have unique “freeze-out” characteristics impacting the relic density, direct and collider search implications, and propose to classify them as pseudofeebly interacting massive particles (pFIMP). The dynamics of pFIMP is studied in a model-independent manner by solving generic coupled Boltzmann equations (cBEQ), followed by a concrete model illustration.

We argue that the boundary of an asymptotically anti–de Sitter (AdS) space of dimension $d+1$, say $M^{d+1}$, can be locally reconstructed from a codimension-two defect located in the deep interior of a negatively curved Einstein manifold $X^{d+2}$ of one higher dimension. This means that there exist two different ways of thinking about the same $d$-submanifold, ${\mathrm{\Sigma }}^d$: either as a defect embedded in the interior of $X^{d+2}$, or as the boundary of $M^{d+1}$ in a certain zero radius limit. Based on this idea and other geometric and symmetry arguments, we propose the existence of an infrared field theory on a bulk ${\mathbb{Z}}_n$-orbifold defect, located in the deepest point of the interior of ${\mathrm{AdS}}^{d+2}$. We further conjecture that such a theory gives rise to the holographic theory at the asymptotic boundary of ${\mathrm{AdS}}^{d+1}$, in the limit where the orbifold parameter $n\to \infty$. As an example, we compute a defect central charge when $\mathrm{\Sigma }$ is a 2-manifold of fixed positive curvature, and show that its $n\to \infty$ limit reproduces the central charge of Brown and Henneaux.

The correlations of electric currents in hot non-Abelian plasma are responsible for the experimental manifestations of the chiral magnetic effect in heavy-ion collisions. We evaluate these correlations using holography, and show that they are driven by large-scale topological fluctuations. In a non-Abelian plasma with chiral fermions, local axial charge can be generated either by topological fluctuations (creating domains with nonzero Chern-Simons number) or by thermal fluctuations. Within holography, we investigate the dynamical creation of the axial charge and isolate the imprint of the topological dynamics on the spatial correlations of electric current. In particular, we show that the spatial extent of the current correlation is quite large ($\sim 1\mathrm{fm}$) and grows with time, which is consistent with sphaleronlike dynamics. We provide numerical estimates for this spatial size that can be used as an input in phenomenological analyses.

We investigate the asymptotic symmetries of three-dimensional AdS Einstein gravity in the Weyl-Fefferman-Graham gauge, which is a generalization of the Fefferman-Graham gauge inducing a Weyl connection as part of the boundary structure. We show that this gauge arises as a natural intermediary step of the gauge-fixing procedure in the Chern–Simons formulation. We prove that the diffeomorphism required to go to the usual Fefferman–Graham gauge can be charged, and thus its implementation has physical repercussions. We discuss the holographic renormalization and the variational principle offering a new holographic take on this gauge and its charges.

In this work, we use gauge/gravity duality to study potential energy and string breaking of triply heavy baryons at finite temperature and chemical potential. Two different possible configurations of triply heavy baryon are considered. The effect of temperature and chemical potential on string-breaking distance is investigated. With increasing temperature/chemical potential, the sting-breaking distance decreases and then increases in symmetric collinear geometry while steadily increasing in equilateral triangle geometry. Our study provides insights into triply heavy baryon configuration and string-breaking behavior.

In this paper, we consider a quantum scalar field propagating on the Reissner-Nordström black hole spacetime. We compute the renormalized stress-energy tensor for the field in the Hartle-Hawking, Boulware and Unruh states. When the field is in the Hartle-Hawking state, we renormalize using the recently developed “extended coordinate” prescription. This method, which relies on Euclidean techniques, is very fast and accurate. Once, we have renormalized in the Hartle-Hawking state, we compute the stress-energy tensor in the Boulware and Unruh states by leveraging the fact that the difference between stress-energy tensors in different quantum states is already finite. We consider a range of coupling constants and masses for the field and a range of electric charge values for the black hole, including near-extreme values. Lastly, we compare these results with the analytic approximations available in the literature.

Hawking radiation can be regarded as a spontaneous and continuous creation of virtual particle-antiparticle pairs outside the event horizon of a black hole where strong tidal forces prevent the annihilation; the particle escapes to infinity contributing to the Hawking flux, while its corresponding antiparticle partner enters the event horizon and ultimately reaches the singularity. The aim of this paper is to investigate the energy density correlations between the Hawking particles and their partners across the event horizon of two models of nonsingular black holes by calculating the two-point correlation function of the density operator of a massless scalar field. This analysis is motivated by the fact that in acoustic black holes particle-partner correlations are signaled by the presence of a peak in the equal-time density-density correlator. Performing the calculation in a Schwarzschild black hole it was shown in Balbinot and Fabbri, [Quantum correlations across the horizon in acoustic and gravitational black holes, Phys. Rev. D 105, 045010 (2022).] that the peak does not appear, mainly because of the singularity. It is then interesting to consider what happens when the singularity is not present. In the Hayward and Simpson-Visser nonsingular black holes we show that the density-density correlator remains finite when the partner particle approaches the hypersurface that replaces the singularity, opening the possibility that partner-particle correlations can propagate towards other regions of spacetime instead of being lost in a singularity.

Binary boson stars can be used to model the nonlinear dynamics and gravitational wave signals of merging ultracompact, but horizonless, objects. However, doing so requires initial data satisfying the Hamiltonian and momentum constraints of the Einstein equations, something that has not yet been addressed. In this work, we construct constraint-satisfying initial data for a variety of binary boson star configurations. We do this using the conformal thin-sandwich formulation of the constraint equations, together with a specific choice for the matter terms appropriate for scalar fields. The free data is chosen based upon a superposition of isolated boson star solutions, but with several modifications designed to suppress the spurious oscillations in the stars that such an approach can lead to. We show that the standard approach to reducing orbital eccentricity can be applied to construct quasicircular binary boson star initial data, reducing the eccentricity of selected binaries to the $\sim {10}^{-3}$ level. Using these methods, we construct initial data for quasicircular binaries with different mass ratios and spins, including a configuration where the spin is misaligned with the orbital angular momentum, and where the dimensionless spins of the boson stars exceeds the Kerr bound. We evolve these to produce the first such inspiral-merger-ringdown gravitational waveforms for constraint-satisfying binary boson stars. Finally, we comment on how equilibrium equations for the scalar matter could be used to improve the construction of binary initial data, analogous to the approach used for quasiequilibrium binary neutron stars.