The interest in the implications that astrophysical observations have for the understanding of the structure of black holes has grown since the first detection of gravitational waves. Many arguments that are put forward in order to constrain alternative black hole models rely on substantial assumptions such as perfect spherical symmetry, which implies absence of rotation. However, given that astrophysical black holes will generally exhibit nonzero angular momentum, realistic constraints must take into account the effects of rotation. In this work we analyze the gravitational effect that rotation has on the emission from the surface of ultracompact objects, by studying how angular momentum affects the propagation of light rays. This allows us to evaluate the reliability of the constraints derived for supermassive black holes (more specifically, Sagittarius A* and M87*) assuming lack of rotation [as presented in A. E. Broderick, A. Loeb, and R. Narayan, Astrophys. J. 701, 1357 (2009); A. E. Broderick et al. Astrophys. J. 805, 179 (2015)]. We find that for rapidly spinning objects rotation can significantly affect the escaping probability of a photon emitted from the surface of the object, with a significant increase at the equatorial regions and a decrease at the poles with respect to the nonrotating case. For not so rapidly spinning black hole candidates like Sagittarius A*, such modifications do not affect significantly the present constraints, which are nevertheless weaker than originally supposed due to the relativistic lensing here considered and additional phenomenological parameters that describe basic processes such as absorption. However, taking into account the angular dependence of the superficial emission of rapidly spinning black hole mimickers will be necessary for future studies of objects like e.g., M87*.

This article is dedicated to the use the MICROSCOPE mission’s data to test chameleon theory of gravity. We take advantage of the technical sessions aimed to characterize the electrostatic stiffness of MICROSCOPE’s instrument intrinsic to its capacitive measurement system. Any discrepancy between the expected and measured stiffness may result from unaccounted-for contributors, i.e., extra forces. This work considers the case of chameleon gravity as a possible contributor. It was previously shown that, in situations similar to these measurement sessions, a chameleon fifth force appears and acts as a stiffness for small displacements. The magnitude of this new component of the stiffness is computed over the chameleon’s parameter space. It allows us to derive constraints by excluding any force inconsistent with the MICROSCOPE data. As expected—since MICROSCOPE was not designed for the purpose of such an analysis—these new bounds are not competitive with state-of-the-art constraints, but they could be improved by a better estimation of all effects at play in these sessions. Hence, our work illustrates this novel technique as a new way of constraining fifth forces.

We study the general embedding of a $P(X,\phi )$ inflationary theory into a two-field theory with a curved field space metric, which was proposed as a possible way to examine the relation between de Sitter swampland conjecture and $k$-inflation. We show that this embedding method fits into the special type of two-field model in which the heavy field can be integrated out at the full action level. However, this embedding is not exact due to the upper bound of the effective mass of the heavy field. We quantify the deviation between the speed of sound calculated via the $P(X,\phi )$ theory and the embedded two-field picture to next leading order terms. We especially focus on the first potential slow-roll parameter defined in the two-field picture and obtain an upper bound on it.

Recently, the NANOGrav Collaboration has reported evidence for a common-spectrum stochastic process, which might be interpreted as the first ever detection of stochastic gravitational wave (GW) background. We discuss the possibility of the signal arising from the first- and second-order GWs in nonstandard cosmological history. We show that the NANOGrav observation can be explained by first-order GWs in the nonstandard thermal history with an early matter-dominated era, whereas the parameter space required to explain the NANOGrav observation in the standard cosmology or in the nonstandard epoch of kination domination is ruled out by the big bang nucleosynthesis and cosmic microwave background observations. For the second-order GWs arising from the large primordial scalar fluctuations, we study the standard radiation domination and two specific nonstandard cases with a few forms of the primordial power spectrum $P_{\zeta }(k)$ to achieve abundant primordial black hole (PBH) production. We find that the NANOGrav observation can be explained with standard radiation domination for all of these $P_{\zeta }(k)$. Furthermore, a dustlike epoch leads to abundant PBH formation for a lower amplitude of $P_{\zeta }(k)$ than the radiation-dominated case and complies with the NANOGrav observation only for a few of the $P_{\zeta }(k)$ forms considered here, where the peak wave number is larger than the wave number range probed by NANOGrav. In this nonstandard epoch, for a broad power spectrum, PBHs are produced in a wide mass range in the planetary mass regime. A nonstandard epoch of kination domination cannot produce enough PBHs for any of the $P_{\zeta }(k)$ if the NANOGrav result is to be satisfied.

Gravitational waves (GWs) induced by scalar curvature fluctuations are an important source of the cosmological GW background and a crucial counterpart of the primordial black hole scenario. However, doubts have been cast on the theoretically predicted induced GW spectrum due to its seeming gauge dependence. In this paper, we shed light on the gauge dependence issue of the induced GW spectrum in general cosmological backgrounds. First, inspired by the Hamiltonian formalism we provide very simple formulas for the tensor modes at second order in cosmological perturbation theory. We also emphasize the difference between observable and gauge invariant variables. Second, we argue that the Newton (or shear-free) gauge is suitable for both the calculation of induced GWs and the physical interpretation. We then show that, most notably, the induced GW spectrum is invariant under a set of reasonable gauge transformations, i.e., physically well behaved on small scales, once the source term has become inactive. This includes the commonly used flat, constant Hubble and synchronous gauges but excludes the comoving slicing gauge. We also show that a particular solution of the GW equation in a dust dominated universe while the source term is active can be gauged away by a small change of gauge.

The overall cosmological parameter tension between the Atacama Cosmology Telescope 2020 fourth data release (ACT) and Planck 2018 data within the concordance cosmological model is quantified using the Suspiciousness statistic to be $2.6\sigma$. Between ACT and the South Pole Telescope (SPT) we find a tension of $2.4\sigma$, and $2.8\sigma$ between ACT and $\mathrm{Planck}+\mathrm{SPT}$ combined. While it is unclear whether the tension is caused by statistical fluctuations, systematic effects or new physics, caution should be exercised in combining these cosmic microwave background datasets in the context of the $\mathrm{\Lambda }\mathrm{CDM}$ standard model of the universe.

Black hole (BH) binary mergers driven by gravitational perturbations of tertiary companions constitute an important class of dynamical formation channels for compact binaries detected by LIGO/VIRGO. Recent works have examined numerically the combined orbital and spin dynamics of BH binaries that undergo large Lidov-Kozai (LK) eccentricity oscillations induced by a highly inclined companion and merge via gravitational wave radiation. However, the extreme eccentricity variations make such systems difficult to characterize analytically. In this paper, we develop an analytical formalism for understanding the spin dynamics of binary BHs undergoing LK-induced mergers. We show that, under certain conditions, the eccentricity oscillations of the binary can be averaged over to determine the long-term behavior of the BH spin in a smooth way. In particular, we demonstrate that the final spin-orbit misalignment angle ${\theta }_{\mathrm{sl}}$ is often related to the binary’s primordial spin orientation through an approximate adiabatic invariant. Our theory explains the “90° attractor” (as found in recent numerical studies) for the evolution of ${\theta }_{\mathrm{sl}}$ when the initial BH spin is aligned with the orbital axis and the octupole LK effects are negligible—such a “90° attractor” would lead to a small binary effective spin parameter ${\chi }_{\mathrm{eff}}\sim 0$ even for large intrinsic BH spins. We calculate the deviation from adiabaticity in closed form as a function of the initial conditions. We also place accurate constraints on when this adiabatic invariant breaks down due to resonant spin-orbit interactions. We consider both stellar-mass and supermassive BH tertiary companions and provide simple prescriptions for determining analytically the final spin-orbit misalignment angles of the merging BH binaries.

Comparable-mass black-hole mergers generically result in moderate to highly spinning holes, whose spacetime curvature will significantly affect nearby matter in observable ways. We investigate how the moderate spin of a postmerger Kerr black hole immersed in a plasma with initially uniform density and uniform magnetic field affects potentially observable accretion rates and energy fluxes. Varying the initial specific internal energy of the plasma over two decades, we find very little change in steady-state mass accretion rate or Poynting luminosity, except at the lowest internal energies, where fluxes do not exhibit steady-state behavior during the simulation timescale. Fixing the internal energy and varying the initial fixed magnetic-field amplitude and orientation, we find that the steady-state Poynting luminosity depends strongly on the initial field angle with respect to the black hole spin axis, while the matter accretion rate is more stable until the field angle exceeds $\sim 45°$. The protojet formed along the black hole spin axis conforms to a thin, elongated cylinder near the hole, while aligning with the asymptotic magnetic field at large distances.

We present first predictions of the cross sections and differential distributions for the exclusive reaction $pp\to pp{K}^{*0}{\overline{K}}^{*0}$ contributing to the $K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}$ channel. The amplitudes for the reaction are formulated within the nonperturbative tensor-Pomeron approach. We consider separately the $f_2(1950)$ $s$-channel exchange mechanism and the $K^{*0}$ $t/u$-channel exchange mechanism, focusing on their specificities. First mechanism is a candidate for the central diffractive production of tensor glueball and the second one is an irreducible continuum. We adjust parameters of our model, assuming the dominance of Pomeron-Pomeron fusion, to the WA102 experimental data. We find that including the continuum contribution alone one can describe the WA102 data reasonably well. We present predictions for the reaction $pp\to pp(K^{*0}{\overline{K}}^{*0}\to K^{+}{K}^{-}{\pi }^{+}{\pi }^{-})$ for the ALICE, ATLAS, CMS and LHCb experiments including typical kinematical cuts. We find from our model a cross sections of $\sigma \cong 17–250\mathrm{nb}$ for the LHC experiments, depending on the assumed cuts. Absorption effects are included in our analysis.

We use the linear sigma model with quarks to find the magnetic-field-induced modifications to the neutral pion mass at one-loop level. The magnetic field effects are introduced by using charged particle propagators in the presence of a magnetic background in the strong field regime. We show that, when accounting for the effects of the magnetic field on the model couplings, the vacuum sigma field, and the neutral pion self-energy, the neutral pion mass decreases monotonically as a function of the field strength. We find an excellent qualitative and quantitative agreement with recent lattice QCD calculations, reproducing the monotonically decreasing trend with the field strength as well as the decrease when lattice data approach the physical vacuum pion mass from larger values.

We present for the first time the exact next-to-leading-order QCD corrections to the light-quark part of the mixed QCD-EW contributions to Higgs production via gluon fusion at the Large Hadron Collider, for a center-of-mass energy of 13 TeV, with exact EW-boson mass dependence. The relevant two-loop real-emission matrix element is computed using a dynamic one-dimensional series expansion strategy whose stability and speed allows for a numerical phase-space integration using local IR subtraction counterterms. For the choice of renormalization (${\mu }_R$) and factorization (${\mu }_F$) scales, ${\mu }_R={\mu }_F=M_H$, we find ${\sigma }_{gg\to H+X}^{({\alpha }_s^2{\alpha }^2+{\alpha }_s^3{\alpha }^2)}=1.467(2{)}_{-14.6\%}^{+18.7\%}({\mu }_R\text{var})\pm 2\%(\mathrm{PDF})\mathrm{pb}$, which we use to provide the best result, including an estimate of suppressed contributions: ${\sigma }_{pp\to H+X}^{(\mathrm{EW},\text{best})}=2.11\pm 0.28(\text{theory})\mathrm{pb}$.

In this paper, we study the thermoelectric behavior of the quark-gluon plasma within the framework of an effective kinetic theory. We adopt a quasiparticle model to incorporate the effects of a thermal medium. The thermoelectric response of the medium is quantified in terms of the Seebeck and Nernst coefficient. Utilizing the relaxation time approximation and Bhatnagar-Gross-Krook collision kernels in an effective Boltzmann equation, we compute the dependence of the Seebeck coefficients on collision temperature and quark chemical potential. We furthermore explore the magnetic field dependence of the thermoelectric effects in a weakly and strongly magnetized medium. The thermoelectric response of a hot QCD medium is shown to be most prominent at low temperatures close to the transition temperature.

We present the performance of a semantic segmentation network, sparsessnet, that provides pixel-level classification of MicroBooNE data. The MicroBooNE experiment employs a liquid argon time projection chamber for the study of neutrino properties and interactions. sparsessnet is a submanifold sparse convolutional neural network, which provides the initial machine learning based algorithm utilized in one of MicroBooNEs ${\nu }_e$-appearance oscillation analyses. The network is trained to categorize pixels into five classes, which are reclassified into two classes more relevant to the current analysis. The output of sparsessnet is a key input in further analysis steps. This technique, used for the first time in liquid argon time projection chambers data and is an improvement compared to a previously used convolutional neural network, both in accuracy and computing resource utilization. The accuracy achieved on the test sample is $\ge 99\%$. For full neutrino interaction simulations, the time for processing one image is $\approx 0.5\sec$, the memory usage is at 1 GB level, which allows utilization of most typical CPU worker machine.

A union of matter bounce and ekpyrotic scenarios is often studied in an attempt to combine the most promising features of these two models. Since nonperturbative quantum geometric effects in loop quantum cosmology (LQC) result in natural bouncing scenarios without any violation of energy conditions or fine tuning, an investigation of matter-ekpyrotic bounce scenario is interesting to explore in this quantum gravitational setting. In this work, we explore this unified phenomenological model for a spatially flat Friedmann-Lemaître-Robertson-Walker (FLRW) universe in LQC filled with dust and a scalar field in an ekpyrotic scenario like negative potential. Background dynamics and the power spectrum of the comoving curvature perturbations are numerically analyzed with various initial conditions and a suitable choice of the initial states. By varying the initial conditions we consider different cases of dust and ekpyrotic field domination in the contracting phase. We use the dressed metric approach to numerically compute the primordial power spectrum of the comoving curvature perturbations which turns out to be almost scale invariant for the modes which exit the horizon in the matter-dominated phase. But, in contrast with a constant magnitude power spectrum obtained under approximation of a constant ekpyrotic equation of state using deformed algebra approach in an earlier work, we find that the magnitude of power spectrum changes during evolution. Our analysis shows that the bouncing regime only leaves imprints on the modes outside the scale-invariant regime. However, an analysis of the spectral index shows inconsistency with the observational data, thus making further improvements in such a model necessary.

The bulk reconstruction program aims to obtain representations of bulk fields as operators in the boundary conformal field theory (CFT). In this paper, we extend the program by obtaining the boundary representation for a scalar field in a rotating BTZ black hole. We find that the representation of the field near the inner horizon shows novel features. We also obtain a representation for fields inside the horizon as operators in a single boundary CFT using mirror operator construction.

We study the scattering problem in the static patch of de Sitter space, i.e., the problem of field evolution between the past and future horizons of a de Sitter observer. We calculate the leading-order scattering for a conformally massless scalar with cubic interaction, as both the simplest case and a warm-up towards Yang-Mills and gravity. Our strategy is to decompose the static-patch evolution problem into a pair of more symmetric evolution problems in two Poincare patches, sewn together by a spatial inversion. To carry this out explicitly, we end up developing formulas for the momentum-space effect of inversions in flat spacetime. The geometric construction of an electron’s 4-momentum and spin vectors from a Dirac spinor turns out to be surprisingly relevant.

We propose a formulation of quantum mechanics in an extended Fock space in which a tensor product structure is applied to time. Subspaces of histories consistent with the dynamics of a particular theory are defined by a direct quantum generalization of the corresponding classical action. The diagonalization of such quantum actions enables us to recover the predictions of conventional quantum mechanics and reveals an extended unitary equivalence between all physical theories. Quantum correlations and coherent effects across time and between distinct theories acquire a rigorous meaning, which is encoded in the rich temporal structure of physical states. Connections with modern relativistic schemes and the path integral formulation also emerge.

We study the thermodynamics of a $d$-dimensional Schwarzschild black hole, also known as a Schwarzschild-Tangherlini black hole, in the canonical ensemble. This generalizes York’s formalism, which has been initially applied to four dimensions and later to five dimensions, to any number $d$ of dimensions. The canonical ensemble, characterized by a cavity of fixed radius $r$ and fixed temperature $T$ at the boundary, allows for two possible black hole solutions in thermal equilibrium, a smaller black hole and a larger black hole. In four and five dimensions, these solutions have a direct exact form, whereas in an arbitrary number of dimensions, one is compelled to resort to approximation schemes or numerical calculations. From the Euclidean action and the path integral approach, we obtain the free energy, the thermodynamic energy, the thermodynamic pressure, and the entropy, of the black hole plus cavity system. The entropy of the system is given by the Bekenstein-Hawking area law. The analysis of the heat capacity of the system shows that the smaller black hole is in unstable equilibrium and the larger black hole is in stable equilibrium. The $d$-dimensional photon sphere radius divides the stability criterion. Indeed, if the cavity’s radius is larger than the photon sphere radius, and so the black hole is small, the system is unstable, if the cavity’s radius is smaller than the photon sphere radius, and so the black hole is large, the system is stable. To study perturbations on the system, a generalized free energy function is obtained that also allows one to understand the possible phase transitions between classical hot flat space and the black holes. The Buchdahl radius, that appears naturally in the general relativistic study of star structure, also shows up in our context; the free energy is zero when the cavity’s radius has the $d$-dimensional Buchdahl radius value. Then, if the cavity’s radius is larger than the Buchdahl radius, classical hot flat space phase cannot make a phase transition to a black hole phase, and if smaller, classical hot flat space can nucleate a black hole. The roles of both the photon sphere and the Buchdahl limit are present for every dimension $d$, indicating that, besides their known role in dynamics, these radii also play a role in the thermodynamics of gravitational systems. The close link between the canonical analysis performed and the direct perturbation of the path integral is also pointed out. Since hot flat space is a quantum system made purely of gravitons, if only gravitation is considered, it is of great interest to compare the $d$-dimensional free energies of quantum hot flat space and the stable black hole to find for which ranges of $r$ and $T$, the quantities that characterize the canonical ensemble, one phase predominates over the other. Phase diagrams for a few different dimensions are displayed. The density of states at a given energy is found through an inverse Laplace transformation giving back the entropy of the stable black hole. Several side calculations and further deliberations are performed, namely, the calculation for the approximate expressions for the canonical ensemble black hole horizon radii, a brief study of the photon orbit radius and the Buchdahl radius in the $d$-dimensional Schwarzschild solution, a connection to the thermodynamics of thin shells in $d$ spacetime dimensions which are systems that are also apt to a rigorous thermodynamic study, a presentation of quantum hot flat space in $d$ spacetime dimensions as a thermodynamic system, an analysis of classical hot flat space in $d$ spacetime dimensions as a product of quantum hot flat space with the black hole transitions and the corresponding phase diagrams for a few different dimensions, and a synopsis with the relevance of the work. It is still worth mentioning that the comparison of the thermodynamics of $d$-dimensional Schwarzschild black holes and classical hot flat space in the canonical ensemble with the thermodynamics of spherical thin shells in $d$ dimensions yields a striking direct matching between the two systems, most notably that the photon sphere radius appears here as a thermodynamic stability divisor in both systems, and the Buchdahl radius that appears on thermodynamic grounds for canonical black holes appears also as a thermodynamic and as a dynamical radius for thin shells.

We present different Taub-NUT/bolt-anti de Sitter (AdS) solutions in a shift-symmetric sector of Horndeski theory of gravity possessing nonminimal kinetic coupling of scalar fields to the Einstein tensor. In four dimensions, we find locally and asymptotically locally AdS solutions possessing nontrivial scalar field. In higher dimensions, analytical Taub-NUT/bolt-AdS $p$-branes and solitons are obtained, supported by the existence of $p$ Horndeski scalar fields with axionic profile. The thermodynamic properties are studied through Euclidean methods and it is found that the first law of thermodynamics is satisfied. Moreover, constraints on the parameter space of Horndeski gravity and NUT charge are obtained by demanding positivity of the mass, entropy, and specific heat of the $p$-branes and soliton. We briefly comment on future applications in holography.

Originally designed for waveform approximants, the effective precession parameter ${\chi }_{\mathrm{p}}$ is the most commonly used quantity to characterize spin-precession effects in gravitational-wave observations of black-hole binary coalescences. We point out that the current definition of ${\chi }_{\mathrm{p}}$ retains some, but not all, variations taking place on the precession timescale. We rectify this inconsistency and propose more general definitions that either fully consider or fully average those oscillations. Our generalized parameter ${\chi }_{\mathrm{p}}\in [0,2]$ presents an exclusive region ${\chi }_{\mathrm{p}}>1$ that can only be populated by binaries with two precessing spins. We apply our prescriptions to current LIGO/Virgo events and find that posterior distributions of ${\chi }_{\mathrm{p}}$ tend to show longer tails at larger values. This appears to be a generic feature, implying that (i) current ${\chi }_{\mathrm{p}}$ measurement errors might be underestimated, but also that (ii) evidence for spin precession in current data might be stronger than previously inferred. Among the gravitational-wave events released to date, that which shows the most striking behavior is GW190521.