Searches for continuous gravitational waves from unknown neutron stars are limited in sensitivity due to their high computational cost. For this reason, developing new methods or improving existing ones can increase the probability of making a detection. In this paper we present a new framework that uses Markov chain Monte Carlo (MCMC) or nested sampling methods to follow up candidates of continuous gravitational-wave searches. This framework aims to go beyond the capabilities of pyfstat (which is limited to the ptemcee sampler), by allowing a flexible choice of sampling algorithm (using bilby as a wrapper) and multidimensional correlated prior distributions. We show that MCMC and nested sampling methods can recover the maximum posterior point for much bigger parameter-space regions than previously thought (including for sources in binary systems), and we present tests that examine the capabilities of the new framework: a comparison between the dynesty, nessai, and ptemcee samplers, the usage of correlated priors, and its improved computational cost.

The present paper is devoted to a study of the equilibrium configurations of slowly rotating anisotropic stars in the framework of general relativity. For that purpose, we provide the equations of structure where the rotation is treated to second order in the angular velocity. These equations extend those first derived by Hartle for slowly rotating isotropic stars. As an application of the new formalism, we study the rotational properties of Bowers-Liang fluid spheres. A result of particular interest is that the ellipticity and mass quadrupole moment are negative for certain highly anisotropic configurations; thus, such systems are prolate rather than oblate. Furthermore, for configurations with high anisotropy and compactness close to their critical value, quantities like the moment of inertia, change of mass, and mass quadrupole moment approach to the corresponding Kerr black hole values, similar to other ultracompact systems like sub-Buchdahl Schwarzschild stars and analytic rotating gravastars.

A key attribute of dark energy is the equation of state parameter $w=\text{pressure}/\text{energy density}$, and this has been recently measured observationally, giving values close to $-1$. In this paper we calculate the $w$ parameter characterizing the novel Weyl scaling invariant dark energy that we have analyzed in a series of papers, and show that it is compatible with experiment. We also derive the atomic electron effective potential induced by dark energy from the electron geodesic equation, which can be applied to the evaluation of energy level shifts in Rydberg atoms.

The memory effect in gravitational waves is a direct prediction of general relativity. The presence of the memory effect in gravitational wave signals not only serves as a test for general relativity but also establishes connections between soft theorem, and asymptotic symmetries, serving as a bridge for exploring fundamental physics. Furthermore, with the ongoing progress in space-based gravitational wave detection projects, the gravitational wave memory effect generated by the merger of massive binary black hole binaries is becoming increasingly significant and cannot be ignored. In this work, we perform the full Bayesian analysis of the gravitational wave memory effect with TianQin. The results indicate that the memory effect has a certain impact on parameter estimation but does not deviate beyond the $1\sigma$ range. Additionally, the Bayes factor analysis suggests that when the signal-to-noise ratio of the memory effect in TianQin is approximately 2.36, the log Bayes factor reaches 8. This result is consistent with the findings obtained from a previous mismatch threshold.

In the present work we study the construction of different thermodynamic descriptions for the Kerr-anti–de Sitter (KadS) black holes. The early versions of the KadS thermodynamics are briefly discussed, highlighting some of its strong points and shortcomings. Isohomogeneous transformations, a procedure for generating new thermodynamics, are presented and geometrically interpreted for KadS. This tool is used to determine possible KadS thermodynamics that can be constructed to satisfy a Smarr formula, and the validity of the first law in the generated thermodynamics. The connection between new thermodynamic theories and early Hawking’s approach is considered. In this new framework, the usual KadS thermodynamics is complemented with its geometric construction, and Hawking’s proposal, which does not satisfy the first law, is improved to an alternative thermodynamic theory. With the quantum statistical relation, Hawking’s and this alternative KadS thermodynamics are also generalized from four to higher dimensions.

Tidal heating in a binary black hole system is driven by the absorption of energy and angular momentum by the black hole’s horizon. Previous works have shown that this phenomenon becomes particularly significant during the late stages of an extreme mass ratio inspiral (EMRI) into a rapidly spinning massive black hole, a key focus for future low-frequency gravitational-wave observations by (for instance) the Laser Interferometer Space Antenna mission. Past analyses have largely focused on quasicircular inspiral geometry, with some of the most detailed studies looking at equatorial cases. Though useful for illustrating the physical principles, this limit is not very realistic astrophysically, since the population of EMRI events is expected to arise from compact objects scattered onto relativistic orbits in galactic centers through many-body events. In this work, we extend those results by studying the importance of tidal heating in equatorial EMRIs with generic eccentricities. Our results suggest that accurate modeling of tidal heating is crucial to prevent significant dephasing and systematic errors in EMRI parameter estimation. We examine a phenomenological model for EMRIs around exotic compact objects by parametrizing deviations from the black hole (BH) picture in terms of the fraction of radiation absorbed compared to the BH case. Based on a mismatch calculation, we find that reflectivities as small as $|\mathcal{R}{|}^2\sim \mathcal{O}({10}^{-5})$ are distinguishable from the BH case, irrespective of the value of the eccentricity. We stress, however, that this finding should be corroborated by future parameter estimation studies.

We present miko, a catalog-to-cosmology pipeline for general flat-sky field-level inference, which provides access to cosmological information beyond the two-point statistics. In the context of weak lensing, we identify several new field-level analysis systematics (such as aliasing, Fourier mode-coupling, and density-induced shape noise), quantify their impact on cosmological constraints, and correct the biases to a percent level. Next, we find that model misspecification can lead to both absolute bias and incorrect uncertainty quantification for the inferred cosmological parameters in realistic simulations. The Gaussian map prior infers unbiased cosmological parameters, regardless of the true data distribution, but it yields overconfident uncertainties. The log-normal map prior quantifies the uncertainties accurately, although it requires careful calibration of the shift parameters for unbiased cosmological parameters. We demonstrate systematics control down to the 2% level for both models, making them suitable for ongoing weak lensing surveys.

Different computational techniques for cosmological phase transition parameters can impact the gravitational wave (GW) spectra predicted in a given particle physics model. To scrutinize the importance of this effect, we perform large-scale parameter scans of the dynamical real-singlet extended Standard Model using three perturbative approximations for the effective potential; the $\overline{\mathrm{MS}}$ and on shell schemes at leading order, and three-dimensional thermal effective theory (3D EFT) at next-to-leading order. While predictions of GW amplitudes are typically unreliable in the absence of higher-order corrections, we show that the reconstructed model parameter spaces are robust up to a few percent in uncertainty. While 3D EFT is accurate from one-loop order, theoretical uncertainties of reconstructed model parameters, using four-dimensional standard techniques, remain dominant over the experimental ones even for signals merely strong enough to claim a detection by LISA.

We investigate the scalar induced gravitational waves (SIGWs) in metric teleparallel gravity with the Nieh-Yan (NY) term, which results in parity violation during the radiation-dominated era. By solving the equations of motion of linear scalar perturbations from both the metric and the tetrad fields, we obtain the corresponding analytic expressions. Then, we calculate the SIGWs in metric teleparallel gravity with the NY term and evaluate the energy density of SIGWs with a monochromatic power spectrum numerically. We find that the spectrum of the energy density of SIGWs in metric teleparallel gravity with the NY term is significantly different from that in general relativity (GR), which makes metric teleparallel gravity distinguishable from GR.

We continue our studies of the evolution and cosmological consequences of current-carrying cosmic string networks, described by a charge-velocity-dependent one scale (CVOS) model. We present a detailed calculation of the effects of these networks on the cosmic microwave background (CMB), in the context of this model, and specifically discuss how such current-carrying strings may be distinguished from their uncharged (Nambu-Goto) counterparts by current or forthcoming CMB data. We find that, under the CVOS hypothesis, the constraints on current-carrying strings should not differ much from those of their structureless counterparts in that the impact on the CMB can at most be reduced by a factor of $\sim 25\%$. Nevertheless, the presence of a current and charge affects the distribution of power among scalar, vector and tensor modes, and also its distribution between small and large scales. It should therefore be possible for future high-sensitivity CMB temperature and polarization experiments to distinguish between the two types of strings.

We analyze theories that do not have a de Sitter vacuum and cannot lead to slow-roll quintessence, but which nevertheless support a transient era of accelerated cosmological expansion due to interactions between a scalar $\varphi$ and either a hidden sector thermal bath, which evolves as dark radiation, or an extremely light component of dark matter. We show that simple models can explain the present-day dark energy of the Universe consistently with current observations. This is possible both when $\varphi$’s potential has a hilltop form and when it has a steep exponential runaway, as might naturally arise from string theory. We also discuss a related theory of multifield quintessence, in which $\varphi$ is coupled to a sector that sources a subdominant component of dark energy, which overcomes many of the challenges of slow-roll quintessence.

In the mixed dark matter scenarios consisting of primordial black holes (PBHs) and particle dark matter (DM), PBHs can accrete surrounding DM particles to form ultracompact minihalos (UCMHs or clothed PBHs) even at an early epoch of the Universe. The distribution of DM particles in a UCMH follows a steeper density profile (${\rho }_{\mathrm{DM}}\propto r^{-9/4}$) compared with a classical DM halo. It is expected that the DM annihilation rate is very large in UCMHs, resulting in a contribution to, e.g., the extragalactic neutrino flux. In this work, we investigate the extragalactic neutrino flux from clothed PBHs due to DM annihilation, and then the muon flux for neutrino detection. Compared with the atmospheric neutrino flux, we derive the upper limits on the cosmological abundance of PBHs for 10 years of exposure time of, e.g., the IceCube experiment. For the DM mass $m_{\chi }=100(1000)\mathrm{GeV}$, the upper limits ($2\sigma$) on the fraction of DM in PBHs are $f_{\mathrm{PBH}}=1.2\times {10}^{-3}(8.9\times {10}^{-5})$ for contained events and $f_{\mathrm{PBH}}=2.5\times {10}^{-3}(1.3\times {10}^{-5})$ for upward events. Compared with other constraints, although the upper limits obtained by us are not the strongest, it is a different way to study the cosmological abundance of PBHs.

We propose a simple model that can alleviate the $H_0$ tension while remaining consistent with big bang nucleosynthesis (BBN). It is based on a dark sector described by a standard Lagrangian featuring a $SU(N)$ gauge symmetry with $N\ge 3$ and a massive scalar field with a quartic coupling. The scalar acts as a dark Higgs leading to spontaneous symmetry breaking $SU(N)\to SU(N-1)$ via a first-order phase transition à la Coleman-Weinberg. This setup naturally realizes previously proposed scenarios featuring strongly interacting dark radiation (SIDR) with a mass threshold within hot new early dark energy. For a wide range of reasonable model parameters, the phase transition occurs between the BBN and recombination epochs and releases a sufficient amount of latent heat such that the model easily respects bounds on extra radiation during BBN while featuring a sufficient SIDR density around recombination for increasing the value of $H_0$ inferred from the cosmic microwave background. Our model can be summarized as a natural mechanism providing two successive increases in the effective number of relativistic degrees of freedom after BBN but before recombination $\mathrm{\Delta }{N}_{\mathrm{BBN}}\to \mathrm{\Delta }{N}_{\mathrm{NEDE}}\to \mathrm{\Delta }{N}_{\mathrm{IR}}$ alleviating the Hubble tension. The first step is related to the phase transition, and the second is related to the dark Higgs becoming nonrelativistic. This setup predicts further signatures, including a stochastic gravitational wave background and features in the matter power spectrum that can be searched for with future pulsar timing and Lyman-$\alpha$ forest measurements.

We simulate multicore merger of fuzzy dark matter in a periodic domain until it relaxes and forms the typical core-halo structure, found both in small domain analyses as well as in structure formation simulations. Using a reference potential gauge invariance of the Schrödinger-Poisson system of equations, we use different values of the reference gravitational potential at the boundaries and illustrate how it affects the core-halo scaling relation of the resulting core-halo structure. This result demonstrates that using different boundary conditions for the reference gravitational potential in various simulations may contribute to the diversity of the scaling relation.

The main aim of this work is to explore the possibility that cold dark matter (CDM) and early dark energy (EDE) can be described by canonical scalar fields that are coupled at the level of its conservation equations. The formalism covers dynamical aspects at the background and linear perturbation levels for an arbitrary coupling function, followed by an example of it. We emphasize the impact of this model on the matter power spectrum and the cosmic microwave background (CMB) spectra, with or without direct interaction. Our findings indicate that the presence of a scalar field can partially counteract the known effects of the other, opening the possibility to avoid some undesired aspects, such as the increase in ${\mathrm{\Omega }}_m$ that usually is needed in the case of a purely EDE scalar field scenario, in order to fit the CMB spectra. This opens up the possibility to analyzing whether the interaction can help to ameliorate the cosmological tensions.

In this paper, we reassess the ability of the acoustic early dark energy (ADE) and axionlike early dark energy (EDE) models to resolve the Hubble tension in light of the new $\mathrm{Pantheon}+$ and $\mathrm{S}{H}_0\mathrm{ES}$ data on the one hand, and the baryon oscillation spectroscopic survey (BOSS) luminous red galaxies (LRG) and extended baryon oscillation spectroscopic survey (eBOSS) quasistellar objects (QSO) data analyzed under the effective field theory of large-scale structures (EFTofLSS) on the other hand. We find that the $\mathrm{Pantheon}+$ data, which favor a larger ${\mathrm{\Omega }}_m$ value than the Pantheon data, have a strong constraining power on the ADE model, while the EFTofLSS analysis of the BOSS and eBOSS data only slightly increases the constraints. We establish that the ADE model is now strongly disfavored as a solution to the Hubble tension, with a remaining tension of $3.6\sigma$ (according to the $Q_{\mathrm{DMAP}}$ metric). In addition, we find that the axionlike EDE model performs better when confronted to the same datasets, with a residual tension of $2.5\sigma$. This work shows that the $\mathrm{Pantheon}+$ data can have a decisive impact on models which aim to resolve the Hubble tension.

In numerical simulations of binary neutron star systems, the equation of state of the dense neutron star matter is an important factor in determining both the physical realism and the numerical accuracy of the simulations. Some equations of state used in simulations are $C^2$ or smoother in the pressure/density relationship function, such as a polytropic equation of state, but may not have the flexibility to model stars or remnants of different masses while keeping their radii within known astrophysical constraints. Other equations of state, such as tabular or piecewise polytropic, may be flexible enough to model additional physics and multiple stars’ masses and radii within known constraints, but are not as smooth, resulting in additional numerical error. We will study in this paper a recently developed family of equation of state, using a spectral expansion with sufficient free parameters to allow for a larger flexibility than current polytropic equations of state, and with sufficient smoothness to reduce numerical errors compared to tabulated or piecewise polytropic equations of state. We perform simulations at three mass ratios with a common chirp mass, using two distinct spectral equations of state, and at multiple numerical resolutions. We evaluate the gravitational waves produced from these simulations, comparing the phase error between resolutions and equations of state, as well as with respect to analytical models. From our simulations, we estimate that the phase difference at the merger for binaries with a dimensionless weighted tidal deformability difference greater than $\mathrm{\Delta }\tilde{\mathrm{\Lambda }}\approx 55$ can be captured by the spectral Einstein code for these equations of state.

The precise and efficient identification of the nature of the primary cosmic rays on an event-by-event basis stands as a fundamental aspiration for any cosmic-ray observatory. In particular, the detection and characterization of gamma ray events are challenged by their occurrence within an overwhelmingly greater flux of charged cosmic rays spanning several orders of magnitude. The intricacies of distinguishing between cosmic ray compositions and the inherent uncertainties associated with hadronic interactions present formidable challenges, which, if not properly addressed, can introduce significant sources of systematic errors. This work introduces a novel composition discriminant variable, $P_{\mathrm{tail}}^{\alpha }$, which quantifies the number of water-Cherenkov detectors (WCDs) with a signal well above the mean signal observed in WCDs located at an equivalent distance from the shower core, in events with approximately the same energy at the ground. This new event variable is then shown to be, in the reconstructed energy range 10 TeV to 1.6 PeV, well correlated with the total number of muons that hit, in the same event, all the observatory stations located at a distance greater than 200 m from the shower core. The two variables should thus have similar efficiencies in the selection of high-purity gamma event samples and in the determination of the nature of charged cosmic ray events.

We highlight the capacity of current and forthcoming air shower arrays using water-Cherenkov stations to detect neutrino events spanning energies from 10 GeV to 100 TeV. This detection approach leverages individual stations equipped with both bottom and top photosensors, making use of features of the signal time trace and machine-learning techniques. Our findings demonstrate the complementary of this method to established and future neutrino-detection experiments, including IceCube and the upcoming Hyper-Kamiokande experiment.

Core-collapse supernovae can be a copious source of sterile neutrinos, hypothetical particles that mix with active neutrinos. We develop two-dimensional stellar core-collapse models that incorporate the mixing between tau neutrinos and heavy sterile neutrinos—those with the mass of 150–200 MeV—to investigate signatures of sterile neutrinos in supernova observables. We find that the decay channel of a sterile neutrino into a pion and a tau neutrino can enhance the explosion energy and the synthesized nickel mass. Although the inclusion of sterile neutrinos considered in this study slightly reduce the neutrino and gravitational-wave signals, we find that they are still detectable for a Galactic event. Furthermore, we point out that if sterile neutrinos are as massive as $\sim 200\mathrm{MeV}$, they produce high-energy tau antineutrinos with energies of $\sim 80\mathrm{MeV}$, the detection of which can be a smoking signature of the sterile neutrinos and where Hyper-Kamiokande should play a pivotal role.