In this paper we present a Bardeen solution surrounded by a cloud of strings fluid. We show how this model has the same event horizon characteristic as the Bardeen solution. However, the parameter of the strings make the solution singular at the origin. We also analyze the solution from a thermodynamic point of view. We calculate the system’s state function, enthalpy, temperature, and other potentials, as a function of entropy. By analyzing the thermodynamic coefficients, we show that the solution presents three distinct phases, two of which are stable and one is unstable. These three phases could be best visualized using a plot of Gibbs free energy versus temperature. Finally, we calculate the critical exponents and find that they are the same as those found in Van der Walls theory.

We revisit the quantum cosmological constant problem and highlight the important roles played by the de Sitter (dS) horizon of zero-point energy. We argue that fields which are light enough to have a dS horizon of zero-point energy comparable to the Friedmann-Lemaître-Robertson-Walker (FLRW) Hubble radius are the main contributors to dark energy. On the other hand, the zero-point energy of heavy fields develop nonlinearities on sub-Hubble scales and cannot contribute to dark energy. We speculate that our proposal may provide a resolution for both the old and new cosmological constant problems by noting that there exists a field, the (lightest) neutrino, which happens to have a mass comparable to the present background photon temperature. The proposal predicts multiple transient periods of dark energy in the early and late expansion history of the Universe, yielding a higher value of the current Hubble expansion rate which can resolve the $H_0$ tension problem.

We present a cosmological analysis using the second and third moments of the weak lensing mass (convergence) maps from the first three years of data (Y3) data of the Dark Energy Survey. The survey spans an effective area of 4139 square degrees and uses the images of over 100 million galaxies to reconstruct the convergence field. The second moment of the convergence as a function of smoothing scale contains information similar to standard shear 2-point statistics. The third moment, or the skewness, contains additional non-Gaussian information. The data is analyzed in the context of the $\mathrm{\Lambda }\mathrm{CDM}$ model, varying five cosmological parameters and 19 nuisance parameters modeling astrophysical and measurement systematics. Our modeling of the observables is completely analytical, and has been tested with simulations in our previous methodology study. We obtain a 1.7% measurement of the amplitude of fluctuations parameter $S_8\equiv {\sigma }_8({\mathrm{\Omega }}_m/0.3{)}^{0.5}=0.784\pm 0.013$. The measurements are shown to be internally consistent across redshift bins, angular scales, and between second and third moments. In particular, the measured third moment is consistent with the expectation of gravitational clustering under the $\mathrm{\Lambda }\mathrm{CDM}$ model. The addition of the third moment improves the constraints on $S_8$ and ${\mathrm{\Omega }}_{\mathrm{m}}$ by $\sim 15\%$ and $\sim 25\%$ compared to an analysis that only uses second moments. We compare our results with Planck constraints from the cosmic microwave background, finding a $2.2–2.8\sigma$ tension in the full parameter space, depending on the combination of moments considered. The third moment, independently, is in $2.8\sigma$ tension with Planck, and thus provides a cross-check on the analyses of 2-point correlations.

It is believed that relic gravitons are squeezed during inflation. If so, quantum noise induced by them can be significantly enhanced in current interferometers. However, decoherence of the gravitons during cosmic history may change the degree of squeezing. As a first step for analyzing the decoherence of the gravitons, we assume the presence of a sizable magnetic field at the beginning of inflation and study conversion processes of the squeezed gravitons into photons during inflation in the case of minimal coupling between gravitons and photons. We solve the dynamical evolution of a coupled system of gravitons and photons perturbatively and obtain squeezing parameters for the system numerically and analytically. It turns out that the gravitons are robust against the decoherence caused by the cosmological magnetic fields. We also find that the conversion rate of gravitons into photons is at a few percent at most.

We examine the vector-portal inelastic dark matter (DM) model with DM mass $m_{\chi }$ and dark photon mass $m_{A^{\prime }}$, in the “forbidden dark matter” regime where $1\lesssim m_{A^{\prime }}/m_{\chi }\lesssim 2$, carefully tracking the dark sector temperature throughout freeze-out. The inelastic nature of the dark sector relaxes the stringent cosmic microwave background (CMB) and self-interaction constraints compared to symmetric DM models. We determine the CMB limits on both annihilations involving excited states and annihilation into $e^{+}{e}^{-}$ through initial-state radiation of an $A^{\prime }$, as well as limits on the DM self-scattering, which proceeds at the one-loop level. The unconstrained parameter space serves as an ideal target for accelerator $A^{\prime }$ searches, and provides a DM self-interaction cross section that is large enough to observably impact small-scale structure.

Within a confining quark matter model which considers phenomenologically the quark confinement and asymptotic freedom as well as the chiral symmetry restoration and quark deconfinement at high baryon density, we find that if the up-down quark matter ($ud\mathrm{QM}$) is more stable than nuclear matter and strange quark matter (SQM), the maximum mass of static quark stars with $ud\mathrm{QM}$ is $2.87M_{\odot }$ under agreement with both the constraints on star tidal deformability from gravitational wave signal GW170817 and the mass-radius of PSR $\mathrm{J}0030+0451$ and PSR $\mathrm{J}0740+6620$ measured by NICER. In contrast, the conventional strange quark star with the SQM that is more stable than nuclear matter while the nuclear matter is more stable than $ud\mathrm{QM}$, has a maximum static mass of only $1.87M_{\odot }$ and its radius significantly deviates from NICER’s constraint. Our results thus provide circumstantial evidence suggesting the recently reported GW190814’s secondary component with a mass of ${2.59}_{-0.09}^{+0.08}{M}_{\odot }$ could be an up-down quark star.

Recently, strong evidence was found for the presence of higher-order modes in the gravitational wave signals GW190412 and GW190814, which originated from compact binary coalescences with significantly asymmetric component masses. This has opened up the possibility of new tests of general relativity by looking at the way in which the higher-order modes are related to the basic signal. Here we further develop a test which assesses whether the amplitudes of subdominant harmonics are consistent with what is predicted by general relativity. To this end we incorporate a state-of-the-art waveform model with higher-order modes and precessing spins into a Bayesian parameter estimation and model selection framework. The analysis methodology is tested extensively through simulations. We investigate to what extent deviations in the relative amplitudes of the harmonics will be measurable depending on the properties of the source, and we map out correlations between our testing parameters and the inclination of the source with respect to the observer. Finally, we apply the test to GW190412 and GW190814, finding no evidence for violations of general relativity.

$B-L$ gauge symmetry is motivated by the successful generation of the seesaw mechanism and leptogenesis. We show that if the $B-L$ gauge boson constitutes a small fraction of dark matter (DM) it can explain the Galactic 511 keV emission via decay into an electron-positron pair. We find the model parameter space that is consistent with the seesaw mechanism, is cosmologically viable, and accounts for the amplitude of the Galactic positron line. From this parameter space, we derive an upper bound on the gauge boson mass and a bound on the positron injection energy $\lesssim 3\mathrm{MeV}$. This derived energy bound is consistent with the observational upper limit of the injection energy. The resultant model predicts the $B-L$ breaking scale to be in a relatively narrow range, i.e., $V_{B-L}\sim {10}^{15}–{10}^{16}\mathrm{GeV}$, which is consistent with a grand unification scale seesaw mechanism. The model is consistent in several phenomenologies, suggesting that they have a common origin in $B-L$ symmetry breaking.

The $U(1{)}_{B\text{−}L}$ symmetry, the essential component in the seesaw mechanism and leptogenesis, is naturally equipped with a massive gauge boson. If this gauge boson is the dark matter, the scenario consistent with the seesaw mechanism predicts the gauge coupling to be of the order of $\mathcal{O}({10}^{-19})$ for masses $\lesssim 1\mathrm{MeV}$, dominantly decaying into active neutrinos. We stress and explore the important role of astrophysical neutrinos of energies from $\mathcal{O}(1)\mathrm{keV}$ to $\sim 1\mathrm{MeV}$ in testing the well-motivated $B\text{−}L$ symmetry extension to the Standard Model, which has been missed in the literature to date. Compared to other dark matter models, the neutrino flux in the sub-MeV energy range is a unique prediction in our setup and, once detected, would serve as a smoking gun for the existence of this $B\text{−}L$ gauge boson and its role as the dark matter particle, opening new windows to tackle cosmological and astrophysical conundra.

We propose the family universal $U(1{)}_X$ models with three right-handed neutrinos by choosing the $U(1{)}_X$ gauge symmetry as a linear combination of $U(1{)}_Y\times U(1{)}_{\chi }$ of $SO(10)$. To be consistent with the quantum gravity effects, we introduced a Dirac fermion $\chi$ as a dark matter candidate, which is odd under the gauged $Z_2$ symmetry after $U(1{)}_X$ breaking. The isospin violation dark matter with $f_n/f_p=-0.7$ can be realized naturally, and thus the LUX, PANDAX, and XENON1T experimental constraints can be evaded. Moreover, we study the masses and mixings for Higgs and gauge bosons, consider the LHC constraints on the $Z^{\prime }$ mass, simulate various constraints from dark matter direct and indirect detection experiments, and then present the viable parameter spaces. To study the LHC $Z^{\prime }$ mass bounds on the generic $U(1{)}_X$ models, we considered four kinds of scenarios, where scenario II with zero $U(1{)}_X$ charge for right-handed up-type quarks can relax the LHC $Z^{\prime }$ mass bound a little bit.

We study azimuthal asymmetries in diffractive $\mathrm{J}/\psi$ production in ultraperipheral heavy-ion collisions at RHIC and LHC energies using the color glass condensate effective theory. Our calculation successfully describes the azimuthal averaged $J/\psi$ production cross section measured by STAR and ALICE. We further predict very large $\cos 2\varphi$ and $\cos 4\varphi$ azimuthal asymmetries for diffractive $J/\psi$ production both in UPCs at RHIC and LHC energies and in eA collisions at EIC energies. These novel polarization dependent observables may provide complementary information for constraining gluon transverse spatial distribution inside large nuclei. As compared to all previous analysis of diffractive $J/\psi$ production, the essential new elements integrated in our theoretical calculations are: the double-slit interference effect, the linear polarization of coherent photons, and the final state soft photon radiation effect.

We apply the diabatic formalism, an extension of the adiabatic approximation inherent to the Born-Oppenheimer (BO) approach of atomic physics, to the problem of mixing between exotic multiquark hadrons and their nearby di-hadron thresholds. The unperturbed BO eigenstates are obtained using the dynamical diquark model, while the diabatic calculation introduces a mixing potential between these states and the threshold states. We solve the resulting coupled Schrödinger equations numerically for hidden-charm tetraquarks of both open and closed strangeness to obtain physical mass eigenvalues, and we explore the di-hadron state content and spatial extent of the eigenstates. As an explicit example, $X(3872)$ emerges with a dominant $D^0{\overline{D}}^{*0}$ component, but also contains a considerable diquark-antidiquark component that can contribute significantly to its radiative decay widths, and this component also generates a full multiplet of other diquark-based exotic hadrons to be compared with experiment.

The charged Higgs boson is a smoking gun of extensions of the standard model with multiple Higgs doublets, and has been searched for at various collider experiments. In this paper, we study the signature of a light charged Higgs boson produced by top quark pairs at the Large Hadron Collider (LHC), with subsequent three-body decays into a $W$ boson and a pair of bottom quarks. Cross sections on final states of two $W$ bosons plus four bottom quarks have been measured by the ATLAS Collaboration at the LHC 13 TeV. We reinterpret the experimental data under the scenario of a light charged Higgs boson and find improved agreements. We obtain the first limit from LHC direct searches on the total branching ratio of the three-body decay, $\mathrm{Br}(t\to H^{+}b)\times \mathrm{Br}(H^{+}\to W^{+}b\overline{b})$, and the strongest direct constraints on the parameter space of a class of type-I two-Higgs-doublet models.

The holographic superconductor is the holographic dual of superconductivity, but there is no Meissner effect in the standard holographic superconductor. This is because the boundary Maxwell field is added as an external source and is not dynamical. We show the Meissner effect analytically by imposing the semiclassical Maxwell equation on the AdS boundary. Unlike in the Ginzburg-Landau (GL) theory, the extreme type I limit cannot be reached even in the $e\to \infty$ limit where $e$ is the $U(1)$ coupling of the boundary Maxwell field. This is due to the bound current which is present even in the pure bulk Maxwell theory. In the bulk 5-dimensional case, the GL parameter and the dual GL theory are obtained analytically for the order parameter of scaling dimension 2.

We investigate the (conformally coupled) scalar field on a general Carrollian spacetime in arbitrary dimension. The analysis discloses electric and magnetic dynamics. For both, we provide the energy and the momenta of the field, accompanied by their conservation equations. We discuss the conservation and nonconservation properties resulting from the existence of conformal isometries and the associated charges. We illustrate those results for a scalar field propagating on the null boundary of four-dimensional Ricci-flat Robinson-Trautman spacetimes.

In accordance with current models of the accelerating Universe as a spacetime with a positive cosmological constant, new results about a cosmological upper bound for the area of stable marginally outer trapped surfaces are found taking into account angular momentum, gravitational waves, and matter. Compared to previous results which take into account only some of the aforementioned variables, the bound is found to be tighter, giving a concrete limit to the size of black holes especially relevant in the early Universe.

We construct spherically symmetric static solutions of the Einstein-Klein-Gordon-Euler system involving a complex scalar field governed by a periodic potential that emerges in models of axionlike particles and fermionic matter modeled by a perfect fluid with a polytropic equation of state. Such solutions describe gravitationally bound composites of fermions and axions, which we dub fermion-axion stars. Sequences of pure axion stars in the existence domain may show the presence of multiple stable branches depending on the value of the decay constant parameter in the potential; this reflects in the appearance of multiple islands of stability in the two-dimensional parameter space of fermion-axion configurations. We investigate the domain of existence for three different values of the decay constant, identifying one or more regions of linear stability, making use of a method we already employed in previous works. We confirm the results from the linear analysis performing fully nonlinear numerical relativity evolutions. In this context, we perform several numerical simulations to identify regions in the parameter space where unstable models face different fates: the collapse to a Schwarzschild black hole, the migration to a stable model, and finally the dispersion of the scalar field together with the dilution of the fermionic matter, which approaches a static fermion star model with very low mass. This latter scenario was never observed in previous models without the periodic potential.

We analyze the formation and evolution of the event horizon of a black hole binary merger when the black holes are charged. We find that the presence of charge influences the properties of the merger and can be useful for investigating the validity of various theories of modified gravity and several proposals for dark matter candidates. It can moreover give insights into various aspects of astrophysical phenomena involving black holes, such as degeneracies in the gravitational wave parameter determination. We perform our analysis both analytically and numerically, in $D=4$ dimensions, in the extreme mass ratio (EMR) limit and compare the results. The development of analytical results in the EMR limit is of uttermost importance in view of the upcoming observations of the LISA interferometer. We then use our analysis to describe how the horizon evolves in time during the merger and to investigate the growth in the area of the event horizon and the duration of the merger. We moreover provide a numerical solution valid in arbitrary dimensions $D\ge 4$ which could be of interest in the context of the $\mathrm{AdS}/\mathrm{CFT}$ correspondence or for examining possible extensions of general relativity.

Black hole spectroscopy with gravitational waves is an important tool to measure the mass and spin of astrophysical black holes and to test their Kerr nature. Next-generation ground- and space-based detectors will observe binary black hole mergers with large signal-to-noise ratios and perform spectroscopy routinely. It was recently shown that small perturbations due, e.g., to environmental effects (the “flea”) to the effective potential governing gravitational-wave generation and propagation in black hole exteriors (the “elephant”) can lead to arbitrarily large changes in the black hole’s quasinormal spectrum, including the fundamental mode, which is expected to dominate the observed signal. This raises an important question: is the black hole spectroscopy program robust against perturbations? We clarify the physical behavior of time-domain signals under small perturbations in the potential, and we show that changes in the amplitude of the fundamental mode in the prompt ringdown signal are parametrically small. This implies that the fundamental quasinormal mode extracted from the observable time-domain signal is stable against small perturbations. The stability of overtones deserves further investigation.

Analytical solutions of nonminimally coupled scalar field cosmology corresponding to critical scalar field values constitute a potential challenge to the recent first-order thermodynamics of scalar-tensor gravity (a formalism picturing general relativity as the zero-temperature equilibrium state for modified gravity). The critical solutions are unstable with respect to homogeneous perturbations, hence unphysical.