We report results from searches for anisotropic stochastic gravitational-wave backgrounds using data from the first three observing runs of the Advanced LIGO and Advanced Virgo detectors. For the first time, we include Virgo data in our analysis and run our search with a new efficient pipeline called pystoch on data folded over one sidereal day. We use gravitational-wave radiometry (broadband and narrow band) to produce sky maps of stochastic gravitational-wave backgrounds and to search for gravitational waves from point sources. A spherical harmonic decomposition method is employed to look for gravitational-wave emission from spatially-extended sources. Neither technique found evidence of gravitational-wave signals. Hence we derive 95% confidence-level upper limit sky maps on the gravitational-wave energy flux from broadband point sources, ranging from $F_{\alpha ,\mathrm{\Theta }}<(0.013–7.6)\times {10}^{-8}\mathrm{erg}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{Hz}}^{-1}$, and on the (normalized) gravitational-wave energy density spectrum from extended sources, ranging from ${\mathrm{\Omega }}_{\alpha ,\mathrm{\Theta }}<(0.57–9.3)\times {10}^{-9}{\mathrm{sr}}^{-1}$, depending on direction ($\mathrm{\Theta }$) and spectral index ($\alpha$). These limits improve upon previous limits by factors of 2.9–3.5. We also set 95% confidence level upper limits on the frequency-dependent strain amplitudes of quasimonochromatic gravitational waves coming from three interesting targets, Scorpius X-1, SN 1987A and the Galactic Center, with best upper limits range from $h_0<(1.7–2.1)\times {10}^{-25}$, a factor of $\ge 2.0$ improvement compared to previous stochastic radiometer searches.

We derive the Boltzmann equation and the collision kernel for massive spin-$1/2$ particles, using the Wigner-function formalism and employing an expansion in powers of $\hslash$. The phase space is enlarged to include a variable related to the spin degrees of freedom. This allows us to reduce the transport equations of the independent components of the Wigner function to one scalar equation. To next-to-leading order in $\hslash$, we find that the collision kernel contains both local and nonlocal terms. We show that off-shell contributions cancel in the Boltzmann equation. Our framework can be used to study spin-polarization phenomena induced by vorticity as recently observed in heavy-ion collisions and in condensed-matter systems.

We construct simple renormalizable extensions of the standard model where the leading baryon number violating processes have $\mathrm{\Delta }B=\pm \mathrm{\Delta }L=-2$. These models contain additional scalars. The simplest models contain a color singlet and a colored sextet. For such a baryon number violation to be observed in experiments, the scalars cannot be much heavier than a few tera-electron-volts. We find that such models are strongly constrained by LHC physics, LEP physics, and flavor physics.

We present a calculation of the charged pion electric polarizability using the background field method. To extract the mass-shift induced by the electric field for the accelerated charged particle we fit the lattice QCD correlators using correlators derived from an effective model. The methodology outlined in this study (boundary conditions, fitting procedure, etc) is designed to ensure that the results are invariant under gauge transformations of the background field. We apply the method to four $N_f=2$ dynamical ensembles to extract ${\alpha }_{{\pi }^{\pm }}$ at pion mass of 315 MeV.

We derive next-to-eikonal (NEik) corrections to the background quark propagator, which stem from (i) considering a finite longitudinal width target instead of an infinitely thin shockwave and (ii) including the interaction of the quark with the transverse components of the background field. These two different corrections to the eikonal approximation combine together and provide a gauge covariant expression for the quark propagator at NEik accuracy. We then apply our results to quark (or antiquark) scattering on a nucleus at NEik accuracy, considering both unpolarized cross section and helicity asymmetry.

For the first time we search for the ${\eta }_{c2}(1D)$ in $e^{+}{e}^{-}\to \gamma {\eta }_{c2}(1D)$ at $\sqrt{s}=10.52$, 10.58, and 10.867 GeV with data samples of $89.5{\mathrm{fb}}^{-1}$, $711{\mathrm{fb}}^{-1}$, and $121.4{\mathrm{fb}}^{-1}$, respectively, accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant ${\eta }_{c2}(1D)$ signal is observed in the mass range between 3.8 and $3.88\mathrm{GeV}/c^2$. The upper limit at 90% confidence level on the product of the Born cross section for $e^{+}{e}^{-}\to \gamma {\eta }_{c2}(1D)$ and branching fraction for ${\eta }_{c2}(1D)\to \gamma h_c(1P)$ is determined to be $\sigma (e^{+}{e}^{-}\to \gamma {\eta }_{c2}(1D))\mathcal{B}({\eta }_{c2}(1D)\to \gamma h_c(1P))<4.9\mathrm{fb}$ at $\sqrt{s}$ near 10.6 GeV.

We consider the twistor space ${\mathcal{P}}^6\cong {\mathbb{R}}^4\times \mathbb{C}{P}^1$ of ${\mathbb{R}}^4$ with a nonintegrable almost complex structure $\mathcal{J}$ such that the canonical bundle of the almost complex manifold $({\mathcal{P}}^6,\mathcal{J})$ is trivial. It is shown that $\mathcal{J}$-holomorphic Chern-Simons theory on a real $(6|2)$-dimensional graded extension ${\mathcal{P}}^{6|2}$ of the twistor space ${\mathcal{P}}^6$ is equivalent to self-dual Yang-Mills theory on Euclidean space ${\mathbb{R}}^4$ with Lorentz invariant action. It is also shown that adding a local term to a Chern-Simons-type action on ${\mathcal{P}}^{6|2}$, one can extend it to a twistor action describing full Yang-Mills theory.

We study quantum gravity effects on the density of states in statistical mechanics and its implications for the critical temperature of a Bose Einstein condensate and fraction of bosons in its ground state. We also study the effects of compact extra dimensions on the critical temperature and the fraction. We consider both neutral and charged bosons in the study and show that the effects may just be measurable in current and future experiments.

We consider the generalization of quantum tunneling transitions in the WKB approximation to the time-independent functional Schrödinger and Wheeler-DeWitt equations. Following a Lorentzian approach, we compute the transition rates among different scalar field vacua and compare with those performed by Coleman and collaborators using the Euclidean approach. For gravity, we develop a general formalism for computing transition rates in Wheeler’s superspace. This is then applied to computing decays in flat space and then to transitions in the presence of gravity. In the latter case we point out the complexities arising from having nonpositive definite kinetic terms illustrating them in the simplified context of minisuperspace. This corresponds to a generalization of the well-known ‘tunneling from nothing’ scenarios. While we can obtain the leading term for the transitions obtained by Euclidean methods we also point out some differences and ambiguities. We show that there is no obstruction to keeping the spherically ($SO(4)$) symmetric closed slicing for the new vacuum after a de Sitter to de Sitter transition. We argue that this is the natural Lorentzian realization of the Coleman-De Luccia instanton and that a closed universe is also obtained if the mini-superspace assumption is relaxed. This is contrary to the open universe predicted by Coleman–De Luccia which relies on an analytic continuation performed after bubble nucleation. Our findings may have important cosmological implications related to the origin of inflation and to the string landscape. In particular, they question the widespread belief that evidence for a closed universe would rule out the string landscape.

Gauge symmetries remove unphysical states and guarantee that field theories are free from the pathologies associated with these states. In this work we find a set of general conditions that guarantee the removal of unphysical states in field theories describing interacting vector fields. These conditions are obtained through the extension of a mechanism for the emergence of gauge symmetries proposed in a previous article [C. Barceló J. High Energy Phys. 10 (2016) 084] in order to account for non-Abelian gauge symmetries, and are the following: low-energy Lorentz invariance, emergence of massless vector fields describable by an action quadratic in those fields and their derivatives, and self-coupling to a conserved current associated with specific rigid symmetries. Using a bootstrapping procedure, we prove that these conditions are equivalent to the emergence of gauge symmetries and, therefore, guarantee that any theory satisfying them must be equivalent to a Yang-Mills theory at low energies.

We analyze and compute the semiclassical stress-energy flux components, the outflux ${⟨T_{uu}⟩}_{\mathrm{ren}}$ and the influx ${⟨T_{vv}⟩}_{\mathrm{ren}}$ ($u$ and $v$ being the standard null Eddington coordinates), at the inner horizon (IH) of a Reissner-Nordström black hole (BH) of mass $M$ and charge $Q$, in the near-extremal domain in which $Q/M$ approaches 1. We consider a minimally-coupled massless quantum scalar field, in both Hartle-Hawking and Unruh states, the latter corresponding to an evaporating BH. The near-extremal domain lends itself to an analytical treatment which sheds light on the behavior of various quantities on approaching extremality. We explore the behavior of the three near-IH flux quantities ${⟨T_{uu}^{-}⟩}_{\mathrm{ren}}^U$, ${⟨T_{vv}^{-}⟩}_{\mathrm{ren}}^U$, and ${⟨T_{uu}^{-}⟩}_{\mathrm{ren}}^H={⟨T_{vv}^{-}⟩}_{\mathrm{ren}}^H$, as a function of the small parameter $\mathrm{\Delta }\equiv \sqrt{1-{(Q/M)}^2}$ (where the superscript “$U$” or “$H$” respectively refers to the Unruh or Hartle-Hawking state and “$-$” refers to the IH value). We find that in the near-extremal domain ${⟨T_{uu}^{-}⟩}_{\mathrm{ren}}^U\cong {⟨T_{uu}^{-}⟩}_{\mathrm{ren}}^H={⟨T_{vv}^{-}⟩}_{\mathrm{ren}}^H$ behaves as $\propto {\mathrm{\Delta }}^5$. In contrast, ${⟨T_{vv}^{-}⟩}_{\mathrm{ren}}^U$ behaves as $\propto {\mathrm{\Delta }}^4$, and we calculate the prefactor analytically. It therefore follows that the semiclassical fluxes at the IH neighborhood of an evaporating near-extremal spherical charged BH are dominated by the influx ${⟨T_{vv}⟩}_{\mathrm{ren}}^U$. In passing, we also find an analytical expression for the transmission coefficient outside a Reissner-Nordström BH to leading order in small frequencies (which turns out to be a crucial ingredient of our near-extremal analysis). Furthermore, we explicitly obtain the near-extremal Hawking-evaporation rate ($\propto {\mathrm{\Delta }}^4$), with an analytical expression for the prefactor (obtained here for the first time to the best of our knowledge).

The direct detection of continuous gravitational waves from pulsars is a much anticipated discovery in the emerging field of multimessenger gravitational wave (GW) astronomy. Because putative pulsar signals are exceedingly weak large amounts of data need to be integrated to achieve desired sensitivity. Contemporary searches use ingenious ad hoc methods to reduce computational complexity. In this paper we provide analytical expressions for the Fourier transform of realistic pulsar signals. This provides description of the manifold of pulsar signals in the Fourier domain, used by many search methods. We analyze the shape of the Fourier transform and provide explicit formulas for location and size of peaks resulting from stationary frequencies. We apply our formulas to analysis of recently identified outlier at 1891.76 Hz.

In this contribution we study the birefringence and the quasinormal modes (QNM) in the eikonal approximation of the Einstein-Euler-Heisenberg black hole (EEH-BH). The EEH-BH is an exact solution of the Einstein equations coupled with the Euler-Heisenberg nonlinear electrodynamics. In the Euler-Heisenberg theory the phenomenon of birefringence arises and then there exists two possible light trajectories in the vicinity of the EEH-BH. On the other hand, using the correspondence between the parameters of the unstable null geodesics and the QNM in the eikonal approximation we have determined the QNM of gravitational and electromagnetic perturbations for both the electric and the magnetic EEH-BH and we compared them with their linear counterpart, the Reissner-Nordström black hole. Regarding electromagnetic perturbations we have to consider that there are two effective optical metrics and to each one corresponds one null geodesic that renders two electromagnetic QNMs from the same compact object.

In this work we show several singularity theorems which can be applied to the Reissner-Nordström spacetime. To date, only two results [Phys. Rev. D 50, 3692 (1994); Lett. Math. Phys. 110, 2383 (2020)] have predicted null incompleteness in this case. In addition, we show that regular black holes in the Bardeen category have noncompact slices without the standard assumption regarding the knowledge of regions at infinity and, therefore, that they exhibit topology changes.

Understanding black hole microstructure via the thermodynamic geometry can provide us with deeper insight into black hole thermodynamics in modified gravities. In this paper, we study the black hole phase transition and Ruppeiner geometry for the $d$-dimensional charged Gauss-Bonnet anti–de Sitter black holes. The results show that the small-large black hole phase transition is universal in this gravity. By reducing the thermodynamic quantities with the black hole charge, we clearly exhibit the phase diagrams in different parameter spaces. Of particular interest is that the radius of the black hole horizon can act as the order parameter to characterize the black hole phase transition. We also disclose that, different from the five-dimensional neutral black holes, the charged ones allow the repulsive interaction among its microstructure for a small black hole of higher temperature. Another significant difference between them is that the microscopic interaction changes during the small-large black hole phase transition for the charged case, where the black hole microstructure undergoes a sudden change. These results are helpful for peeking into the microstructure of charged black holes in the Gauss-Bonnet gravity.

Four components of the axisymmetric Einstein equations in $2+1$ dimensions with negative cosmological constant can be written as ${\nabla }_{a}M=\dots$ and ${\nabla }_{a}J=\dots$, where the dots stand for stress-energy terms, and $M$ and $J$ are scalars. In vacuum, they reduce to the constant mass and angular momentum parameters of the BTZ solution of the same name. The integrability conditions for the Einstein equations give rise to two conserved stress-energy currents ${\nabla }_a{j}_{(M)}^a=0$ and ${\nabla }_a{j}_{(J)}^a=0$. The angular momentum current is just the Noether current due to axisymmetry, but the mass current is unexpected in the presence of rotation. The conserved quantity $M$ exists in all dimensions in spherical symmetry, known as the Misner-Sharp, Hawking or Kodama mass, but in $2+1$ dimensions $M$ exists also in axisymmetry, even with rotation. We use $M$ and $J$ to give a fully constrained formulation of the axisymmetric Einstein equations in $2+1$ dimensions, where the Einstein equations are solved by explicit integration from the center along time slices. We use the two conserved matter currents in the construction of a high-resolution shock-capturing formulation of the Einstein-perfect fluid system, in which $M$ and $J$ momentum are then exactly conserved by construction. We demonstrate convergence of the code in the test cases of generic dispersion and collapse and stable and unstable rotating stars.

Gravitational wave observations of compact binaries allow us to test general relativity (and modifications thereof) in the strong and highly dynamical field regime of gravity. Here, we confront two extensions to general relativity, dynamical Chern-Simons, and Einstein-dilaton-Gauss-Bonnet theories, against the gravitational wave sources from the GWTC-1 and GWTC-2 catalogs by the LIGO-Virgo Collaboration. By stacking the posterior of individual events, we strengthen the constraint on the square root of the coupling parameter in Einstein-dilaton-Gauss-Bonnet gravity to $\sqrt{{\alpha }_{\mathrm{EdGB}}}<1.7\mathrm{km}$, but we are unable to place meaningful constraints on dynamical Chern-Simons gravity. Importantly, we also show that our bounds are robust to (i) the choice of general-relativity base waveform model, upon which we add modifications, (ii) unknown higher post-Newtonian order terms in the modifications to general relativity, (iii) the small-coupling approximation, and (iv) uncertainties on the nature of the constituent compact objects.

To date, close to 50 black hole binary mergers were observed by the LIGO and Virgo detectors. The analyses have been done with an assumption that these objects are black holes by limiting the spin prior to the Kerr bound. However, the above assumption is not valid for superspinars, which have the Kerr geometry but rotate beyond the Kerr bound. In this study, we investigate whether and how the limited spin prior range causes a bias in parameter estimation for superspinars if they are detected. To this end, we estimate binary parameters of the simulated inspiral signals of the gravitational waves of compact binaries by assuming that at least one component of them is a superspinar. We have found that when the primary is a superspinar, both mass and spin parameters are biased in parameter estimation due to the limited spin prior range. In this case, the extended prior range is strongly favored compared to the limited one. On the other hand, when the primary is a black hole, we do not see much bias in parameter estimation due to the limited spin prior range, even though the secondary is a superspinar. We also apply the analysis to black hole binary merger events GW170608 and GW190814, which have a long and loud inspiral signal. We do not see any preference of superspinars from the model selection for both events. We conclude that the extension of the spin prior range is necessary for accurate parameter estimation if highly spinning primary objects are found, while it is difficult to identify superspinars if they are only the secondary objects. Nevertheless, the bias in parameter estimation of spin for the limited spin prior range can be a clue of the existence of superspinars.

X-ray reflection spectroscopy is a powerful technique for probing the nature of gravity around black holes in the so-called strong-field regime. One popular approach is to look at theory-agnostic deviations away from the Kerr solution, which is the only astrophysically relevant black hole solution within classical general relativity, in order to verify whether astrophysical black holes are described by the Kerr metric. We have recently extended our x-ray reflection spectroscopy framework to a class of very general axisymmetric non-Kerr black holes proposed by Konoplya, Rezzolla, and Zhidenko [Phys. Rev. D 93, 064015 (2016)]. Here, we analyze XMM-Newton and NuSTAR observations of the supermassive black hole in the Seyfert 1 galaxy MCG–06–30–15 with six different deviation parameters of this extended model. We recover the Kerr solution in all cases, but some deformation parameters are poorly constrained. We discuss the implications of this verification and future possibilities.