Future searches for a gravitational-wave background using Earth-based gravitational-wave detectors might be impacted by correlated noise sources. A well-known example are the Schumann resonances, which are extensively studied in the context of searches for a gravitational-wave background. Earlier work has shown that a technique termed “gravitational-wave geodesy” can be used to generically differentiate observations of a gravitational-wave background from signals due to correlated terrestrial effects, requiring true observations to be consistent with the known geometry of our detector network. The key result of this test is a Bayes factor between the hypotheses that a candidate signal is astrophysical or terrestrial in origin. Here, we further formalize the geodesy test, mapping distributions of false-alarm and false-acceptance probabilities to quantify the degree with which a given Bayes factor will boost or diminish our confidence in an apparent detection of the gravitational-wave background. To define the false alarm probability of a given Bayes factor, we must have knowledge of our null hypothesis: the space of all possible correlated terrestrial signals. Since we do not have this knowledge, we instead construct a generic space of smooth functions in the frequency domain using Gaussian processes, which we tailor to be conservative. This enables us to use draws from our Gaussian processes as a proxy for all possible nonastrophysical signals. During the O2 observing run, the LIGO and Virgo collaborations observed an $\mathrm{SNR}=1.25$ excess in their search for an isotropic gravitational-wave background. To demonstrate the utility of gravitational-wave geodesy, we apply the method to the observed cross-correlated data.

We exploit a recent nonperturbative determination of the momentum broadening kernel $C(b_{\perp })$ in impact parameter space [G. D. Moore, S. Schlichting, N. Schlusser, and I. Soudi, J. High Energy Phys. 10 (2021) 059], to determine the momentum space broadening kernel $C(q_{\perp })$ in high-temperature QCD plasmas. We show how to use the nonperturbatively determined kernel $C(q_{\perp })$ to compute the medium-induced splitting rates in a QCD plasma of finite size. We compare the resulting in-medium splitting rates to the results obtained with leading-order and next-to-leading-order perturbative determinations of $C(q_{\perp })$, as well as with various approximations of the splitting employed in the literature. Generally, we find that the differences in the splitting rates due to the momentum broadening kernel are larger than the errors associated with approximations of the splitting rate.

We discuss stiffening of dense matter in two color QCD (${\mathrm{QC}}_2\mathrm{D}$) where hadrons are mesons and diquark baryons. We study two models which describe a transition of matter from the Bose-Einstein-condensation regime at low density to the Bardeen-Cooper-Schrieffer regime at high density. The first model is based on coherent states of diquarks, and the second is the Nambu-Jona-Lasinio model with diquark pairing terms. We particularly focus on how quark states are occupied as baryon density increases. We find that, due to the occupied quark levels, the ideal gas picture of diquarks breaks down at density significantly less than the density where baryon cores overlap. The saturation of quark states at low momenta stiffens equations of state. We also study the effects of interactions which depend on the quark occupation probability. We argue that equations of state become very stiff when the bulk part of the quark Fermi sea has the effective repulsion but the Fermi surface enjoys the attractive correlations. This disparity for different momentum domains is possible due to the strong channel dependence in gluon exchanges with momentum transfer of 0.2–1 GeV. These concepts can be transferred from ${\mathrm{QC}}_2\mathrm{D}$ to QCD in any numbers of colors.

Models with light dark sector and dark matter particles motivate qualitatively new collider searches. Here we carry out a comprehensive study of hadrophilic models with ${\mathrm{U}(1)}_B$ and ${\mathrm{U}(1)}_{B-3L_{\tau }}$ gauge bosons coupled to light dark matter. The new mediator particles in these models couple to quarks, but have suppressed couplings to leptons, providing a useful foil to the well-studied dark photon models. We consider current bounds from accelerator and collider searches, rare anomaly-induced decays, neutrino nonstandard interactions, and dark matter direct detection. Despite the many existing constraints, these models predict a range of new signatures that can be seen in current and near future experiments, including dark gauge boson decays to the hadronic final states ${\pi }^{+}{\pi }^{-}{\pi }^0$, ${\pi }^0\gamma$, $K^{+}{K}^{-}$, and $K_S{K}_L$ in FASER at LHC Run 3, enhancements of ${\nu }_{\tau }$ scattering rates in far-forward neutrino detectors, and thermal dark matter scattering in FLArE in the HL-LHC era. These models therefore motivate an array of different experiments in the far-forward region at the LHC, as could be accommodated in the proposed Forward Physics Facility.

The light-quark mass dependence of the nucleon axial isovector charge ($g_A$) has been studied up to next-to-next-to-leading order, $\mathcal{O}(p^4)$, in relativistic chiral perturbation theory using extended-on-mass-shell renormalization, without and with explicit $\mathrm{\Delta }(1232)$ degrees of freedom. We show that in the $\mathrm{\Delta }$-less case, at this order, the flat trend of $g_A(M_{\pi })$ exhibited by state-of-the-art lattice QCD (LQCD) results cannot be reproduced using low energy constants extracted from pion-nucleon elastic and inelastic scattering. A satisfactory description of these LQCD data is only achieved in the theory with $\mathrm{\Delta }$. From this fit, we report $g_A(M_{\pi (\mathrm{phys})})=1.260\pm 0.012$, close to the experimental result, and $d_{16}=-0.88\pm 0.88{\mathrm{GeV}}^{-2}$, in agreement with its empirical value. The large uncertainties are of theoretical origin, reflecting the difference between $\mathcal{O}(p^3)$ and $\mathcal{O}(p^4)$ that still persists at large $M_{\pi }$ in presence of the $\mathrm{\Delta }$.

We attempt to address the question of whether standard tests of general relativity can detect the presence of a black hole carrying a supertranslation field. In this regard, we study the photon sphere of a dynamical black hole carrying a supertranslation hair. We find that the dynamics of the photon sphere is quite subtle and it may offer an opportunity to differentiate a supertranslated black hole from its bald counterpart. This represents a first step toward understanding the observational signatures of a supertranslated dynamical black hole.

In this work, we investigate warm inflationary models in the context of a general scalar-tensor theory of gravity which is coupled to radiation through a dissipation term. We first derive the potential of exponential and hyperbolic tangent forms. We consider a dissipation parameter of the form $\mathrm{\Gamma }=C_{1}T$ with $C_1$ being a coupling parameter and focus only on the strong regime of which the interaction between inflaton and radiation fluid has been taken into account. We compute inflationary observables and constrain the parameters of our model using current Planck 2018 data. From our analysis, we discover that the weak coupling limit $\xi \ll 1$ is needed in order to have the derived $n_s$ and $r$ consistent with the Planck 2018 observational constraints. Particularly, we constrain the potential scale $V_0$ of the models.

Obtaining a high-quality interaction model with associated uncertainties is essential for neutrino experiments studying oscillations, nuclear scattering processes, or both. As a primary input to the MicroBooNE experiment’s next generation of neutrino cross section measurements and its flagship investigation of the MiniBooNE low-energy excess, we present a new tune of the charged-current pionless ($\mathrm{CC}0\pi$) interaction cross section via the two major contributing processes—charged-current quasielastic and multinucleon interaction models—within version 3.0.6 of the GENIE neutrino event generator. Parameters in these models are tuned to muon neutrino $\mathrm{CC}0\pi$ cross section data obtained by the T2K experiment, which provides an independent set of neutrino interactions with a neutrino flux in a similar energy range to MicroBooNE’s neutrino beam. Although the fit is to muon neutrino data, the information carries over to electron neutrino simulation because the same underlying models are used in GENIE. A number of novel fit parameters were developed for this work, and the optimal parameters were chosen from existing and new sets. We choose to fit four parameters that have not previously been constrained by theory or data. Thus, this will be called a theory-driven tune. The result is an improved match to the T2K $\mathrm{CC}0\pi$ data with more well-motivated uncertainties based on the fit.

We consider the response of an Unruh-DeWitt detector near an extremal charged black hole, modeling the near-horizon region of this extremal spacetime by the Bertotti-Robinson spacetime. The advantage of employing the Bertotti-Robinson limit is that the two-point functions for a massless scalar field are obtainable in closed form for the field in a number of quantum states of interest. We consider the detector coupled to a massless field in both the Boulware vacuum state and arbitrary thermal states, including the Hartle-Hawking state, and analyze the detector’s response for a broad range of trajectories. Particular attention is paid to the thermalization of the detector, the anti-Unruh and anti-Hawking effect.

We examine the question of scale vs conformal invariance for the linearized Einstein-Hilbert action, which describes the IR fixed point of quantum gravity. In $D=4$, although the action is not conformally invariant in the usual sense, we explicitly show that the theory is a conformal field theory at the level of correlation functions. In higher dimensions, we show that the theory is scale but not conformally invariant, but can be embedded into a larger nonunitary conformal field theory, analogous to what has been found for Maxwell theory in $D>4$. We give evidence that similar statements are true for all free higher-spin theories.

We study biantisymmetric tensor quantum field theories with $O(N_1)\times O(N_2)$ symmetry. Working in $4-\epsilon$ dimensions we calculate the beta functions up to second order in the coupling constants and analyze in detail the renormalization group (RG) flow and its fixed points. We allow $N_1$ and $N_2$ to assume general real values and treat them as bifurcation parameters. In studying the behavior of these models in a nonunitary regime in the space of $N_1$ and $N_2$ we find a point where a zero-Hopf bifurcation occurs. In the vicinity of this point, we provide analytical and numerical evidence for the existence of Shilnikov homoclinic orbits, which induce chaotic behavior in the RG flow of a subset of nearby theories. As a simple warm-up example for the study of chaotic RG flows, we also review the non-Hermitian Ising chain and show how, for special complex values of the coupling constant, its RG transformations are equivalent to the Bernoulli map.

Bearing in mind our previous study on asymptotic behavior of null geodesics near future null infinity, we analyze the behavior of geometrical quantities such as a certain extrinsic curvature and Riemann tensor in the Bondi coordinates. In the sense of asymptotics, the condition for an $r$-constant hypersurface to be a photon surface is shown to be controlled by a key quantity that determines the fate of photons initially emitted in angular directions. In four dimensions, such a nonexpanding photon surface can be realized even near future null infinity in the presence of enormous energy flux for a short period of time. By contrast, in higher-dimensional cases, no such a photon surface can exist. This result also implies that the dynamically transversely trapping surface, which is proposed as an extension of a photon surface, can have an arbitrarily large radius in four dimensions.

Black holes carrying a magnetic monopole charge have been a subject of interest for a long time. In this work we explore the possibility of an observational evidence of such black holes carrying a magnetic monopole, namely the Bardeen rotating black holes. We derive the theoretical spectrum from the accretion disk surrounding a Bardeen black hole using the thin-disk approximation. We compare the theoretically derived spectrum with the optical data of eighty Palomar Green quasars to constrain the monopole charge parameter $g$ and the spin parameter $a$ of the quasars. From our analysis we note that the Kerr-scenario in general relativity is observationally more favored than black holes with a monopole charge. We arrive at such a conclusion using error estimators like ${\chi }^2$, the Nash-Sutcliffe efficiency, the index of agreement and their modified forms. In particular, black holes with $g\ge 0.03$ (in the unit of the black hole mass) is outside 99% confidence interval. The implications are discussed.

It is known that the gravitational analog of the Faraday rotation arises in the rotating spacetime due to the nonzero gravitomagnetic field. In this paper, we show that it also arises in the “nonrotating” Reissner-Nordström spacetime, if it is immersed in a uniform magnetic field. The nonzero angular momentum (due to the presence of electric charge and magnetic field) of the electromagnetic field acts as the twist potential to raise the gravitational Faraday rotation as well as the gravitational Stern-Gerlach effect in the said spacetimes. The twisting can still exist even if the mass of the spacetime vanishes. In other words, the massless charged particle(s) immersed in a uniform magnetic field are able to twist the spacetime in principle, and are responsible for the rotation of the plane of polarization of light. This, in fact, could have applications in the basic physics and the analog models of gravity. Here, we also study the effect of magnetic fields in the Kerr and Reissner-Nordström spacetimes, and we derive the exact expressions for the gravitational Faraday rotation and the gravitational Stern-Gerlach effect in the magnetized Kerr and Reissner-Nordström spacetimes. Calculating the lowest order of the gravitational Faraday effect arisen due to the presence of a magnetic field, we show that the logarithm correction of the distance of the source and observer in the gravitational Faraday rotation and gravitational Stern-Gerlach effect for the said spacetimes is an important consequence of the presence of the magnetic field. From the astrophysical point of view, our result could be helpful to study the effects of (gravito)magnetic fields on the propagation of polarized photons in the strong gravity regime of the collapsed object.

We study the critical gravitational collapse of a massless scalar field nonminimally coupled to gravity, using a quadratic coupling function with a strength parameter $\xi$. We concentrate on critical phenomena of type II, and determine with an accuracy of at least ${10}^{-12}$ the value of the critical amplitude for collapse to a black hole, as well as the values of the critical and echoing exponents. Obtaining such high accuracy in the critical amplitude requires us to do a coordinate radial transformation that effectively increases resolution near the central regions by a factor of at least ${10}^3$. As expected, we find that for the case of small coupling the critical behavior is very similar to that of a minimally coupled scalar field. On the other hand, for high coupling the dynamics become so violent that we need to introduce a special slicing condition, known as the shock-avoiding slicing condition, in order to avoid gauge pathologies that would otherwise cause our simulations to fail. With this new gauge condition we are able to perform high-accuracy simulations even in the strong-coupling regime, where we find that the critical and echoing exponents become significantly smaller, and that the echoing behavior is richer and cannot be modeled by a single harmonic.

The light rings (LRs) topological charge (TC) of a spacetime measures the number of stable LRs minus the number of unstable LRs. It is invariant under smooth spacetime deformations obeying fixed boundary conditions. Asymptotically flat equilibrium black holes (BHs) have, generically, $\mathrm{TC}=-1$. In Einstein-Maxwell theory, however, the Schwarzschild-Melvin BH—describing a neutral BH immersed in a strong magnetic field—has $\mathrm{TC}=0$. This allows the existence of BHs without LRs and produces remarkable phenomenological features, like panoramic shadows. Here we investigate the generalized Schwarzschild-Melvin solution in Einstein-Maxwell-dilaton theory, scanning the effect of the dilaton coupling $a$. We find that the TC changes discontinuously from $\mathrm{TC}=0$ to $\mathrm{TC}=-1$ precisely at the Kaluza-Klein value $a=\sqrt{3}$, when the (empty) Melvin solution corresponds to a twisted Kaluza-Klein reduction of five-dimensional flat spacetime, i.e., the dilaton coupling $a$ induces a topological transition in the TC. We relate this qualitative change to the Melvin asymptotics for different $a$. We also study the shadows and lensing of the generalized Schwarzschild-Melvin solution for different values of $a$, relating them to the TC.

A massive astrophysical object deforms the local distribution of dark matter, resulting in a local overdensity of dark matter. This phenomenon is often referred to as gravitational focusing. In the solar system, the gravitational focusing due to the Sun induces modulations of dark matter signals on terrestrial experiments. We consider the gravitational focusing of light bosonic dark matter with a mass of less than about 10 eV. The wave nature of such dark matter candidates leads to unique signatures in the local overdensity and in the spectrum, both of which can be experimentally relevant. We provide a formalism that captures both the gravitational focusing and the stochasticity of wave dark matter, paying particular attention to the similarity and difference to particle dark matter. Distinctive patterns in the density contrast and spectrum are observed when the de Broglie wavelength of dark matter becomes comparable or less than the size of the system and/or when the velocity dispersion of dark matter is sufficiently small. While gravitational focusing effects generally remain at a few percent level for a relaxed halo dark matter component, they could be much larger for dark matter substructures. With a few well-motivated dark matter substructures, we investigate how each substructure responds to the gravitational potential of the Sun. The limit at which wave dark matter behaves similar to particle dark matter is also discussed.

Spectral representations have been shown to provide an efficient way to represent the poorly understood high-density portion of the neutron-star equation of state. This paper shows how the efficiency and accuracy of those representations can be improved by a very simple change.

We present a search for dark photon dark matter that could couple to gravitational-wave interferometers using data from Advanced LIGO and Virgo’s third observing run. To perform this analysis, we use two methods, one based on cross-correlation of the strain channels in the two nearly aligned LIGO detectors, and one that looks for excess power in the strain channels of the LIGO and Virgo detectors. The excess power method optimizes the Fourier transform coherence time as a function of frequency, to account for the expected signal width due to Doppler modulations. We do not find any evidence of dark photon dark matter with a mass between $m_{\mathrm{A}}\sim {10}^{-14}–{10}^{-11}\mathrm{eV}/c^2$, which corresponds to frequencies between 10–2000 Hz, and therefore provide upper limits on the square of the minimum coupling of dark photons to baryons, i.e., $U(1{)}_{\mathrm{B}}$ dark matter. For the cross-correlation method, the best median constraint on the squared coupling is $\sim 1.31\times {10}^{-47}$ at $m_{\mathrm{A}}\sim 4.2\times {10}^{-13}\mathrm{eV}/c^2$; for the other analysis, the best constraint is $\sim 2.4\times {10}^{-47}$ at $m_{\mathrm{A}}\sim 5.7\times {10}^{-13}\mathrm{eV}/c^2$. These limits improve upon those obtained in direct dark matter detection experiments by a factor of $\sim 100$ for $m_{\mathrm{A}}\sim [2–4]\times {10}^{-13}\mathrm{eV}/c^2$, and are, in absolute terms, the most stringent constraint so far in a large mass range $m_A\sim 2\times {10}^{-13}–8\times {10}^{-12}\mathrm{eV}/c^2$.

Decoherence dynamics of quarkonia is studied in the high-temperature deconfined phase of $\mathrm{SU}(N_c)$ gauge theories. In particular, we analyze the symmetry properties of $\mathrm{SU}(N_c)$ stochastic potential model and find a novel “event-by-event” symmetry for the $N_c=2$ case, similar to the $G$-parity of hadronic systems. This novel symmetry constrains the relation between diagonal and off-diagonal components of quarkonium density matrix, leaving the latter to be finite at late times. We also present a one-dimensional numerical simulation of the model, which indicates the usefulness of the complex potential simulations for the quarkonium survival probabilities in relativistic heavy-ion collisions, provided that the effect of dissipation can be neglected.