We investigate the correlation between the distribution of galaxies and the predicted gravitational-wave background of astrophysical origin. We show that the large angular scale anisotropies of this background are dominated by nearby nonlinear structure, which depends on the notoriously hard to model galaxy power spectrum at small scales. In contrast, we report that the cross-correlation of this signal with galaxy catalogues depends only on linear scales and can be used to constrain the average contribution to the gravitational-wave background as a function of time. Using mock data based on a simplified model, we explore the effects of galaxy bias, angular resolution and the matter abundance on these constraints. Our results suggest that, when combined with galaxy surveys, the gravitational-wave background can be a powerful probe for both gravitational-wave merger physics and cosmology.

We have studied the effects of anisotropies on the momentum transport in a strongly interacting matter by the transport coefficients, viz. shear ($\eta$) and bulk ($\zeta$) viscosities. The anisotropies could arise either by the strong magnetic field or by the preferential expansion, both of which are created in the very early stages of ultrarelativistic heavy ion collisions at the RHIC or the LHC. This study is thereby aimed to understand (i) the fluidity and location of the transition point of the matter through $\eta /s$ and $\zeta /s$ ($s$ is the entropy density), respectively, (ii) the sound attenuation through the Prandtl number (Pl), (iii) the nature of the flow by the Reynolds number (Rl), and (iv) the competition between momentum and charge diffusions through the ratio $(\eta /s)/({\sigma }_{\mathrm{el}}/T)$. For this purpose, we have first calculated the viscosities in the relaxation-time approximation of kinetic theory approach and the interactions among partons are embodied by assigning masses to quarks and gluons at finite temperature and strong magnetic field, known as the quasiparticle model. Compared to the isotropic medium, both $\eta$ and $\zeta$ get increased in the magnetic field-driven ($B$-driven) anisotropy, contrary to the decrease in the expansion-driven anisotropy. Zooming in, $\eta$ increases with temperature faster in the former case than in the latter case, whereas $\zeta$ in the former case monotonically decreases with the temperature and in the latter case, it is meager and ultimately diminishes at a specific temperature. Thus, the behaviors of shear and bulk viscosities could in principle distinguish the aforesaid anisotropies. As a result, $\eta /s$ gets enhanced in the former case but decreases with temperature and in the latter case, it becomes even smaller than the isotropic one. Similarly, $\zeta /s$ gets amplified but decreases faster with the temperature in the presence of a strong magnetic field. The Prandtl number gets increased in $B$-induced anisotropy and gets decreased in expansion-induced anisotropy, compared to the isotropic case. However, Pl is always found larger than 1, so the sound attenuation is mostly governed by the momentum diffusion. The momentum anisotropy due to the magnetic field makes the Reynolds number smaller than 1, whereas the expansion-driven anisotropy makes it larger. Finally the ratio $(\eta /s)/({\sigma }_{\mathrm{el}}/T)$ is amplified much in the presence of magnetic field-driven anisotropy, whereas the amplification is less pronounced in an isotropic medium as well as in an expansion-driven anisotropic medium. However, the ratio is always more than 1, so the momentum diffusion always prevails over the charge diffusion.

The fireball concept of Hagedorn, developed in the 1960s, is an alternative description of hadronic matter. Using a recently derived description yielding the mass spectrum and the dynamics, we use the transport model GiBUU to calculate the shear viscosity of a gas of such Hagedorn states, applying the Green-Kubo method to Monte Carlo calculations. Since the entropy density is rising ad infinitum near $T_H$, this leads to a very low shear viscosity to entropy density ratio near $T_H$. Further, by comparing our results with analytic expressions, we find a nice extrapolation behavior, indicating that a gas of Hagedorn states comes close to or even goes below the boundary $1/4\pi$ from $\mathrm{AdS}/\mathrm{CFT}$.

We consider the scattering of dark matter particles from superfluid liquid ${}^4\mathrm{He}$, which has been proposed as a target for their direct detection. Focusing on dark matter masses below $\sim 1\mathrm{MeV}$, we demonstrate from sum-rule arguments the importance of the production of single phonons with energies $\omega \lesssim 1\mathrm{meV}$. We show further that the anomalous dispersion of phonons in liquid ${}^4\mathrm{He}$ at low pressures [i.e., $d^2\omega (q)/d{q}^2>0$, where $q$ and $\omega (q)$ are the phonon momentum and energy] has the important consequence that a single phonon will decay over a relatively short distance into a shower of lower-energy phonons centered on the direction of the original phonon. Thus, the experimental challenge in this regime is to detect a shower of low-energy phonons, not just a single phonon. Additional information from the distribution of phonons in such a shower could enhance the determination of the dark matter mass.

In this paper, analogies between multiparticle production in high-energy collisions and the time evolution of the early Universe are discussed. A common explanation is put forward under the assumption of an unconventional early state: a rapidly expanding universe before recombination (last scattering surface), followed by the cosmic microwave background, later evolving up to present days, versus the formation of hidden/dark states in hadronic collisions followed by a conventional QCD parton shower yielding final-state particles. In particular, long-range angular correlations are considered pointing out deep connections between the two physical cases potentially useful for the discovery of new physics.

According to the Standard Model (SM), we expect to find a proton for each decaying neutron. However, the experiments counting the number of decayed neutrons and produced protons disagree. This discrepancy suggests that neutrons might have an exotic decay channel to Dark Sector (DS) particles. In this paper, we explore a scenario where neutrons decay to a dark Dirac fermion $\chi$ and a non-Abelian dark gauge boson $W^{\prime }$. In our proposed scenario, the DS has three portals with the SM sector: (1) the fermion portal coming from the mixing of the neutron with $\chi$, (2) a scalar portal, and (3) a nonrenormalizable kinetic mixing between photon and dark gauge bosons which induces a vector portal between the two sectors. We discuss the cosmological implications of this scenario assuming DS particles are produced via freeze-in. The fermion and the scalar portal leads to the overproduction of DS particles by the time of the Cosmic Microwave Background (CMB), and thus we disable these two portals in the early universe. For that, we require the maximum temperature of the universe to be lower than $m_{\chi }$. We rely on the vector portal to connect the two sectors in the early universe, and we discuss the phenomenological bounds on the model. The main constraints come from the Big Bang Nucleosynthesis, ensuring the right relic abundance of dark matter, and the observation of large neutron stars.

In the present work, the mass spectra of doubly heavy tetraquarks $T_{Q{Q}^{\prime }}$ are systematically investigated in a relativized quark model. The four-body systems including the Coulomb potential, confining potential, spin-spin interactions, and relativistic corrections are solved within the variational method. Our results suggest that the $I{J}^P=01^{+}bb\overline{u}\overline{d}$ state is 54 MeV below the relevant $\overline{B}{\overline{B}}^{*}$ thresholds, which indicates that both strong and electromagnetic decays are forbidden, and thus this state can be a stable one. Its large hidden color component and small root mean square radius demonstrate that it is a compact tetraquark rather than a loosely bound molecule or pointlike diquark-antidiquark structure. Our predictions of the doubly heavy tetraquarks may provide valuable information for future experimental searches.

We explicitly demonstrate how to correctly define the hadronic parton distributions [parton distribution functions (PDFs), transverse-momentum-dependent parton distribution functions, and generalized parton distributions] in the soft-wall anti–de Sitter/QCD approach, based on the use of a quadratic dilaton field, providing confinement and breaking of conformal and chiral symmetries. The power behavior of parton distributions at large values of the light-cone variable is consistent with quark counting rules and Drell-Yan-West duality. All parton distributions are defined in terms of profile functions, which depend on the light-cone coordinate and are fixed from PDFs and electromagnetic form factors.

Based on the observation that the exterior space-times of Schwarzschild-type solutions allow two symmetric slicings, a static spherically symmetric one and a timelike homogeneous one, modifications of gravitational dynamics suggested by symmetry-reduced models of quantum cosmology can be used to derive corresponding modified spherically symmetric equations. Generally covariant theories are much more restricted in spherical symmetry compared with homogeneous slicings, given by $1+1$-dimensional dilaton models if they are local. As shown here, modifications used in loop quantum cosmology do not have a corresponding covariant spherically symmetric theory. Models of loop quantum cosmology therefore violate general covariance in the form of slicing independence. Only a generalized form of covariance with a non-Riemannian geometry could consistently describe space-time in models of loop quantum gravity.

We argue that the complex transformation relating the Schwarzschild to the Taub-NUT metric, introduced by Talbot, is in fact an electric-magnetic duality transformation. We show that at null infinity, the complex transformation is equivalent to a complexified Bondi-Metzner-Sachs supertranslation, which rotates the supertranslation and the dual (magnetic) supertranslation charges. This can also be seen from the cubic coupling between the classical source and its background, which for Taub-NUT is given by a complex phase rotation acting on gravitational minimal couplings. The same phase rotation generates dyons from electrons at the level of minimally coupled amplitudes, manifesting the double copy relation between the two solutions.

We extend on-shell bootstrap methods from spacetime amplitudes to the world sheet objects of the Cachazo-He-Yuan formalism. We observe that the integrands corresponding to tree-level nonlinear sigma model, Yang-Mills and $(DF{)}^2$ theory are determined by demanding enhanced UV scaling under Britto-Cachazo-Feng-Witten shifts. Back in spacetime, we also find that $(DF{)}^2$ theory is fixed by gauge invariance/UV scaling and simple locality assumptions.

We determine, for the first time, the scaling dimensions of a family of fixed-charge operators stemming from the critical $O(N)$ model in $4-\epsilon$ dimensions to the leading and next to leading order terms in the charge expansion but to all orders in the coupling. We test our results to the maximum known order in perturbation theory while determining higher order terms.

We compute the discharging rate of a uniform electric field due to Schwinger pair production in ($1+1$)-dimensional scalar electrodynamics with a compact dimension of radius $R$. Our calculation is performed in real time, using the in-in formalism. For large compactification radii, $R\to \infty$, we recover the standard noncompact space result. However, other ranges of values of $R$ and of the mass $m$ of the charged scalar give rise to a richer set of behaviors. For $R\gtrsim \mathcal{O}(1/m)$ with $m$ large enough, the electric field oscillates in time, whereas for $R\to 0$ it decreases in steps. We discuss the origin of these results.

In this work, we calculate the deflection angle of light in a spacetime that interpolates between regular black holes and traversable wormholes, depending on the free parameter of the metric. Afterwards, this angular deflection is substituted into the lens equations which allows us to obtain physically measurable results, such as the position of the relativistic images and the magnifications.

The influence of considering a generalized dark matter (GDM) model, which allows for a non-pressure-less dark matter and a nonvanishing sound speed in the nonlinear spherical collapse model is discussed for the Einstein-de Sitter-like and $\mathrm{\Lambda }\mathrm{GDM}$ models. By assuming that the vacuum component responsible for the accelerated expansion of the Universe is not clustering and therefore behaving similarly to the cosmological constant $\mathrm{\Lambda }$, we show how the change in the GDM characteristic parameters affects the linear density threshold for collapse of the nonrelativistic component (${\delta }_{\mathrm{c}}$) and its virial overdensity (${\mathrm{\Delta }}_{\mathrm{V}}$). We found that a positive GDM equation of state parameter, $w_{\mathrm{gdm}}$, is responsible for lower values of ${\delta }_{\mathrm{c}}$ as compared to the standard spherical collapse model and that this effect is much stronger than the one induced by a change in the GDM sound speed, $c_{s,\mathrm{gdm}}^2$. We also found that ${\mathrm{\Delta }}_{\mathrm{V}}$ is only slightly affected and mostly sensitive to $w_{\mathrm{gdm}}$. These effects could be relatively enhanced for lower values of the matter density. We found that the effects of the additional physics on ${\delta }_{\mathrm{c}}$ and ${\mathrm{\Delta }}_{\mathrm{V}}$, when translated to nonlinear observables such as the halo mass function, induce an overall deviation of about 40% with respect to the standard $\mathrm{\Lambda }\mathrm{CDM}$ model at late times for high mass objects. However, within the current constraints for $c_{s,\mathrm{gdm}}^2$ and $w_{\mathrm{gdm}}$, we found that these changes are the consequence of properly taking into account the correct linear matter power spectrum for the GDM model while the effects coming from modifications in the spherical collapse model remain negligible. Using a phenomenologically motivated approach, we also study the nonlinear matter power spectrum and found that the additional properties of the dark matter component lead, in general, to a strong suppression of the nonlinear power spectrum with respect to the corresponding $\mathrm{\Lambda }\mathrm{CDM}$ one. Finally, as a practical example, we compare $\mathrm{\Lambda }\mathrm{GDM}$ and $\mathrm{\Lambda }\mathrm{CDM}$ using galaxy cluster abundance measurements, and found that these small scale probes will allow us to put more stringent constraints on the nature of dark matter.

In this paper, we investigate the parameter space in the framework of hilltop supernatural inflation in which the inflaton field can play the role of Affleck-Dine field to produce successful baryogenesis. The suitable value of reheating temperature could coincide with the reheating temperature required to produce lightest supersymmetric particle dark matter. The baryon isocurvature perturbation is shown to be negligible. We consider $p=3$, $p=4$, and $p=6$ type III hilltop inflation and discuss how to connect the models to supersymmetric theories.

Recent studies have theoretically investigated the atomic excitation and ionization induced by the dark matter–nucleus scattering, and it was found that the suddenly recoiled atom is much more likely to excite or lose its electrons than expected. This phenomenon is called the “Migdal effect.” In this paper, we extend the established strategy to describe the Migdal effect in isolated atoms to the case in semiconductors under the framework of the tight-binding approximation. Since the localized aspects of electrons are respected in the form of the Wannier functions, the extension of the existing Migdal approach for isolated atoms is much more natural, while the extensive nature of electrons in solids is reflected in the hopping integrals. We take a diamond target as a concrete proof of principle for the methodology, and calculate relevant energy spectra and the projected sensitivity of such a diamond detector. It turns out that our method as a preliminary attempt is theoretically self-consistent and practically effective.

We investigate the use of hybrid equations of state in binary neutron-star simulations in full general relativity, where thermal effects are included in an approximate way through the adiabatic index ${\mathrm{\Gamma }}_{\mathrm{th}}$. We employ a newly developed finite-temperature equation of state derived in the Brueckner-Hartree-Fock approach and carry out comparisons with the corresponding hybrid versions of the same equation of state, investigating how different choices of ${\mathrm{\Gamma }}_{\mathrm{th}}$ affect the gravitational-wave signal and the hydrodynamical properties of the remnant. We also perform comparisons with the widely used Steiner-Fischer-Hempel equation of state, detailing the differences between the two cases. Overall, we determine that when using a hybrid equation of state in binary neutron-star simulations, the value of the thermal adiabatic index ${\mathrm{\Gamma }}_{\mathrm{th}}\approx 1.7$ best approximates the dynamical and thermodynamical behavior of matter computed using complete, finite-temperature equations of state.

The possible formation of stellar-mass binary black holes through dynamical interactions in dense stellar environments predicts the existence of binaries with non-negligible eccentricity in the frequency band of ground-based gravitational-wave detectors; the detection of binary black hole mergers with measurable orbital eccentricity would validate the existence of this formation channel. Waveform templates currently used in the matched-filter gravitational-wave searches of LIGO-Virgo data neglect effects of eccentricity which is expected to reduce their efficiency to detect eccentric binary black holes. Meanwhile, the sensitivity of coherent unmodeled gravitational-wave searches (with minimal assumptions about the signal model) has been shown to be largely unaffected by the presence of even sizable orbital eccentricity. In this paper, we compare the performance of two state-of-the-art search algorithms recently used by LIGO and Virgo to search for binary black holes in the second observing run (O2), quantifying their search sensitivity by injecting numerical relativity simulations of inspiral-merger-ringdown eccentric waveforms into O2 LIGO data. Our results show that the matched-filter search pycbc performs better than the unmodeled search coherent WaveBurst for the high chirp mass ($>20M_{\odot }$) and low eccentricity region ($e_{30\mathrm{Hz}}<0.3$) of parameter space. For moderate eccentricities and low chirp mass, on the other hand, the unmodeled search is more sensitive than the modeled search.

For broadband quantum noise reduction of gravitational-wave detectors, frequency-dependent squeezed vacuum states realized using a filter cavity is a mature technique and will be implemented in Advanced LIGO and Advanced Virgo from the fourth observation run. To obtain the benefit of frequency-dependent squeezing, detuning and alignment of the filter cavity with respect to squeezed vacuum states must be controlled accurately. To this purpose, we suggest a new length and alignment control scheme, using coherent control sidebands which are already used to control the squeezing angle. Since both squeezed vacuum states and coherent control sidebands have the same mode matching conditions and almost the same frequency, detuning and alignment of the filter cavity can be controlled accurately with this scheme. In this paper, we show the principle of this scheme and its application to a gravitational-wave detector.