We compute the far-from-equilibrium dynamics of relativistic scalar quantum fields in $3+1$ space-time dimensions starting from over-occupied initial conditions. We determine universal scaling exponents and functions for two-point correlators and the four-vertex in a self-similar regime in time and space or momenta. The scaling form of the momentum-dependent four-vertex exhibits a dramatic fall-off toward low momenta. Comparing spectral functions (commutators) and statistical correlations (anticommutators) of field operators allows us to detect strong violations of the fluctuation-dissipation relation in this non-perturbative infrared regime. Based on a self-consistent expansion in the number of field components to next-to-leading order, a wide range of interaction strengths is analyzed and compared to weak-coupling estimates in effective kinetic theory and classical-statistical field theory.

We investigate the conformal window of four-dimensional gauge theories with fermionic matter fields in multiple representations. Of particularly relevant examples are the ultraviolet complete models with fermions in two distinct representations considered in the context of composite Higgs and top partial-compositeness. We first discuss various analytical approaches to unveil the lower edge of the conformal window and their extension to the multiple matter representations. In particular, we argue that the scheme-independent series expansion for the anomalous dimension of a fermion bilinear at an infrared fixed point, ${\gamma }_{\overline{\chi }\chi ,\mathrm{IR}}$, combined with the conjectured critical condition, ${\gamma }_{\overline{\chi }\chi ,\mathrm{IR}}=1$ or equivalently ${\gamma }_{\overline{\chi }\chi ,\mathrm{IR}}(2-{\gamma }_{\overline{\chi }\chi ,\mathrm{IR}})=1$, can be used to determine the boundary of conformal phase transition on fully physical grounds. In illustrative cases of $SU(2)$ and $SU(3)$ theories with $N_R$ Dirac fermions in various representations, we assess our results by comparing to other analytical or lattice results.

We present the results of the first complete calculation of the tree-level $2\to 2$ high-energy scattering amplitudes of the longitudinal modes of massive spin-2 Kaluza-Klein (KK) states, both in the case where the internal space is a torus and in the Randall-Sundrum model where the internal space has constant negative curvature. While individual contributions to this amplitude grow as $\mathcal{O}(s^5)$, we demonstrate explicitly that intricate cancellations occur between different contributions, reducing the growth to $\mathcal{O}(s)$, a slower rate of growth than previously argued in the literature. These cancellations require subtle relationships between the masses of the Kaluza-Klein states and their interactions, and reflect the underlying higher-dimensional diffeomorphism invariance. Our results provide fresh perspective on the range of validity of (effective) field theories involving massive spin-2 KK particles, with significant implications for the theory and phenomenology of these states.

Spin correlations in the t-channel single top quark production and its subsequent decay are investigated for the case of contributions involving anomalous $Wtb$ couplings. We obtain analytical expressions for the differential widths of the three-particle decay of a polarized t quark in its rest frame and also expressions for the differential cross sections of the full process of production and decay of the t quark ($2\to 4$) as a function of the energy of a charged lepton and two angles of orientation of the quantization axis of the t-quark spin. The expression is presented in the most general form for the case of real and imaginary vector and tensor anomalous $Wtb$ couplings. We show that shapes of certain multidimensional kinematic distributions of final state particles are significantly different for the contributions proportional to different combinations of the anomalous couplings. The most noticeable differences appear in the shape of the surfaces of two-dimensional distributions, where one of the variables is the energy of a charged lepton and the other is one of the t-quark spin orientation angles. Observed properties are confirmed by two methods of computations either from the obtained symbolic expression for the differential cross sections of the full process of the polarized single top quark production with its subsequent decay or by means of the comphep program for the complete process involving the t-channel single top. In addition, using the obtained analytical expressions, we estimate the statistical accuracy of extracting values of the anomalous $Wtb$ couplings for different levels of the expected integral luminosity at the LHC.

We canonically quantize ($2+1$)-dimensional electrodynamics including a higher-derivative Chern-Simons term. The effective theory describes a standard photon and an additional degree of freedom associated with a massive ghost. We find the Hamiltonian and the algebra satisfied by the field operators. The theory is characterized by an indefinite metric in the Hilbert space that brings up questions on causality and unitarity. We study both of the latter fundamental properties and show that microcausality as well as perturbative unitarity up to one-loop order are conserved when the Lee-Wick prescription is employed.

To explain the baryon asymmetry of the Universe, we extend the Standard Model (SM) with two additional Higgs doublets with small vacuum expectation values. The additional Higgs fields interact with SM fermions through complex Yukawa couplings, leading to new sources of $CP$ violation. We propose a simple flavor model with $\mathcal{O}(1)$ or smaller Yukawa couplings for quarks and charged leptons, consistent with current flavor constraints. To generate neutrino masses and the baryon asymmetry, right-handed neutrinos in the $\sim 0.1–10\mathrm{TeV}$ range couple to the “Higgs troika.” The new Higgs doublet masses are at or above the TeV scale, allowing for asymmetric decays into SM lepton doublets and right-handed neutrinos. The asymmetry in lepton doublets is then processed into a baryon asymmetry, similar to leptogenesis. Since the masses of the new fields could be near the TeV scale, there is potentially a rich high energy collider phenomenology, including observable deviations in the 125 GeV Higgs decay into muons and taus, as well as detectable low energy signals such as the electron electric dipole moment or $\mu \to e\gamma$. Hence, this is in principle a testable model for the generation of baryon asymmetry.

The muon decay-at-rest ($\mu \text{−}\mathrm{DAR}$) facility provides us with an ideal platform to probe purely muonic charged-current nonstandard neutrino interactions (NSIs). We propose to probe this class of NSI effects using antineutrinos from a $\mu \text{−}\mathrm{DAR}$ source in conjunction with neutrinos from the future Tokai to Kamioka superbeam experiment with megaton hyper Kamiokande detector (T2HK). Even though muonic NSIs are absent in neutrino production at T2HK, we show that our proposed hybrid setup comprising $\mu \text{−}\mathrm{DAR}$ and T2HK helps in alleviating the parameter degeneracies that can arise in data. Analytic considerations reveal that the oscillation probability is most sensitive to the NSI parameter in the $\mu$-e sector. For this parameter, we show that the $\mu \text{−}\mathrm{DAR}$ setup can improve on the existing bounds down to around 0.01, especially when the data are combined with neutrino data from T2HK experiment due to the lifting of parameter degeneracies. The high precision with which $\mu \text{−}\mathrm{DAR}$ can measure ${\delta }_{\mathrm{CP}}$ is shown to be robust even in the presence of the considered NSIs. Finally, we show that the combination of $\mu \text{−}\mathrm{DAR}$ along with T2HK can also be used to put mild constraints on the NSI phase in the vicinity of the maximal CP-violating value, for the chosen benchmark value of ${ϵ}_{\mu e}^{\mu e}=0.01$.

We calculate the variation of the chiral condensate in medium with respect to the quark chemical potential and evaluate the pion-nucleon sigma term via the Hellmann-Feynman theorem. The variation of the chiral condensate in medium is obtained by solving the truncated Dyson-Schwinger equation for the quark propagator at finite chemical potential, with various ansätz for the quark-gluon vertex and gluon propagator. We obtain the value of the sigma term ${\sigma }_{\pi N}=62(1)\mathrm{MeV}$, where the (1) represents the systematic error due to our different ansätz for the quark-gluon vertex and gluon propagator. Our result favors a relatively large value and is rather consistent with the recent data obtained by analyzing pion-nucleon scattering and pionic-atom experiments.

We introduce a new family of tensorial field theories by coupling different fields in a nontrivial way, with a view towards the investigation of the coupling between matter and gravity in the quantum regime. As a first step, we consider the simple case with two tensors of the same rank coupled together, with Dirac like a kinetic kernel. We focus especially on rank-3 tensors, which lead to a power counting just-renormalizable model, and interpret Feynman graphs as Ising configurations on random lattices. We investigate the renormalization group flow for this model, using two different and complementary tools for approximations, namely, the effective vertex expansion method and finite-dimensional vertex expansion for the flowing action. Due to the complicated structure of the resulting flow equations, we divided the work into two parts. In this first part, we only investigate the fundamental aspects on the construction of the model and the different ways to get tractable renormalization group equations, while their numerical analysis will be addressed in a companion paper.

We investigate the geodesic deviation equation in the context of quantum improved spacetimes. The improved Raychaudhuri equation is derived, and it is shown that the classical strong energy condition does not necessarily lead to the convergence of geodesics in a congruence in the quantum improved spacetime.

Gravitational wave echoes have been proposed as a smoking-gun signature of exotic compact objects with near-horizon structure. Recently there have been observational claims that echoes are indeed present in stretches of data from Advanced LIGO and Advanced Virgo immediately following gravitational wave signals from presumed binary black hole mergers, as well as a binary neutron star merger. In this paper we deploy a morphology-independent search algorithm for echoes introduced by Tsang et al. [Phys. Rev. D 98, 024023 (2018)], which (a) is able to accurately reconstruct a possible echoes signal with minimal assumptions about their morphology, and (b) computes Bayesian evidences for the hypotheses that the data contain a signal, an instrumental glitch, or just stationary, Gaussian noise. Here we apply this analysis method to all the significant events in the first Gravitational Wave Transient Catalog (GWTC-1), which comprises the signals from binary black hole and binary neutron star coalescences found during the first and second observing runs of Advanced LIGO and Advanced Virgo. In all cases, the ratios of evidences for signal versus noise and signal versus glitch do not rise above their respective “background distributions” obtained from detector noise, the smallest $p$-value being 3% (for event GW170823). Hence we find no statistically significant evidence for echoes in GWTC-1.

The gravitational lensing of gravitational waves might cause beat patterns detectable by interferometers. The feature of this kind of signal is the existence of the beat pattern in the early inspiral phase, followed by a seemingly randomly changing profile. After the strain peaks for the first time, the signal takes the usual waveform and the strain peaks for the second time. Once this signal is detected, the actual magnification factors can be obtained, so the true luminosity distance of the binary system is known. If the lens can be described by a point mass or a singular isothermal sphere, the functional forms of the time delay and the magnification factors are simple enough, so we can infer the mass of the lens or the cosmological parameters.

We obtain two exact solutions of Einstein gravity coupled to nonlinear electrodynamics (NLED) in ($2+1$)-dimensional anti–de Sitter (AdS) spacetime. The solutions are characterized by the mass $M$, angular momentum $J$, cosmological constant or (anti) de Sitter parameter $\mathrm{\Lambda }$, and an electromagnetic parameter $Q$, that is related to an electric field in the first solution and to a magnetic charge for the second solution. Depending on the range of the parameters, the solutions admit a charged rotating asymptotically AdS black hole (BH) interpretation or a charged rotating asymptotically AdS traversable wormhole (WH). If the electromagnetic field is turned off, the stationary Bañados-Teitelboim-Zanelli (BTZ) BH is recovered; in such a way that our BH-WH solutions are nonlinear charged generalizations of the stationary BTZ-BH. Moreover, in contrast to the BTZ metric, the derived AdS solutions are singular at certain radius $r_s\ne 0$, resembling the ring singularity of the Kerr-Newman spacetime; while if $\mathrm{\Lambda }$ is positive the curvature invariants of the second solution are finite.

In searching for continuous gravitational waves over very many ($\approx {10}^{17}$) templates, clustering is a powerful tool which increases the search sensitivity by identifying and bundling together candidates that are due to the same root cause. We implement a deep learning network that identifies clusters of signal candidates in the output of continuous gravitational wave searches and assess its performance. For loud signals, our network achieves a detection efficiency higher than 97% with a very low false alarm rate and maintains a reasonable detection efficiency for signals with lower amplitudes, i.e., at $\lesssim$ current upper limit values.

We consider an Einstein-aether scalar field cosmological model where the aether and the scalar field are interacting. The model of our consideration consists of the two different interacting models proposed in the literature by Kanno et al. and Donnelly et al. We perform an extended analysis for the cosmological evolution as it is provided by the field equations by using methods from dynamical systems; specifically, we determine the stationary points and we perform a stability analysis of those exact solutions.

Black hole spacetimes, like the Kerr spacetime, admit both stable and plunging orbits, separated in parameter space by the separatrix. Determining the location of the separatrix is of fundamental interest in understanding black holes, and is of crucial importance for modeling extreme-mass-ratio inspirals. Previous numerical approaches to locating the Kerr separatrix were not always efficient or stable across all of parameter space. In this paper we show that the Kerr separatrix is the zero set of a single polynomial in parameter space. This gives two main results. First, we thoroughly analyze special cases (extreme Kerr, polar orbits, etc.), finding strict bounds on the limits of roots, and unifying a number of results in the literature. Second, we pose a stable numerical method which is guaranteed to quickly and robustly converge to the separatrix. This new approach is implemented in the Black Hole Perturbation Toolkit, and results in a $\sim 45\times$ speedup over the prior robust approach.

We consider scalar dark-matter models where the theory has a shift symmetry only broken by the scalar mass term. We restrict ourselves to $k$-essence kinetic terms where the shift symmetric part of the Lagrangian is a function of the first derivatives of the scalar field only. When the scalar mass is much larger than the inverse of the astrophysical time and length scales of interest, these models provide a description of dark-matter equivalent to the one given by theories with only polynomial interactions, in the low-amplitude regime where the self-interactions are small contributions to the Lagrangian. In this regime and in the nonrelativistic limit, which apply on large galactic scales, scalar clouds form solitons with a finite core. This provides an adequate model for dark-matter halos with no singular behavior. Close to the center of galaxies, where a supermassive black hole (BH) resides, we analyze the scalar-field distribution and the fate of the dark-matter soliton when subject to the BH gravitational attraction. We show that the scalar-field profile around such a central BH can be described by new oscillatory solutions of a modified Klein-Gordon equation, which generalize the harmonic oscillations of free scalar dark matter in a flat environment and the Jacobi elliptic functions of the ${\varphi }^4$ model. Moreover, we find that, depending on the form of the $k$-essence kinetic term, regular solutions can be constructed or not, which connect the relativistic ingoing wavelike profile of the scalar field at the BH horizon to the nearly static nonrelativistic soliton at large distance. These profiles have a constant flux and represent the slow infall of scalar matter into the BH. We show that this regular behavior is only possible for $k$-essence functions that satisfy the usual conditions for the absence of ghosts and gradient instabilities, together with a new restriction on the growth of the kinetic function $K(X)$ for large argument. It turns out that the same conditions of stability guarantee that quantum corrections are tamed, provided that the mass of the scalar field is less than ${10}^{-3}\mathrm{eV}$ and the strong coupling scale of the model $\mathrm{\Lambda }$ is much larger than the scalar mass.

The late time acceleration of the Universe can be characterized in terms of an extra, time-dependent, component of the Universe—dark energy. The simplest proposal for dark energy is a scalar-tensor theory—quintessence—which consists of a scalar field, $\varphi$, whose dynamics is solely dictated by its potential, $V(\varphi )$. Such a theory can be uniquely characterized by the equation of state of the scalar field energy momentum-tensor. We find the time dependence of the equation of state for a broad family of potentials and, using this information, we propose an analytic prior distribution for the most commonly used parametrization. We show that this analytic prior can be used to accurately predict the distribution of observables for the next generation of cosmological surveys. Including the theoretical priors in the comparison with observations considerably improves the constraints on the equation of state.

Electron-positron annihilation largely occurs in local thermal and chemical equilibrium after the neutrinos fall out of thermal equilibrium and during the big bang nucleosynthesis (BBN) epoch. The effects of this process are evident in BBN yields as well as the relativistic degrees of freedom. We self-consistently calculate the collision integral for electron-positron creation and annihilation using the Klein-Nishina amplitude and appropriate statistical factors for Fermi blocking and Bose enhancement. Our calculations suggest that this annihilation freezes out when the photon-electron-positron-baryon plasma temperature is approximately 16 keV, after which its rate drops below the Hubble rate. In the temperature regime near 16 keV, we break the assumption of chemical equilibrium between the electrons, positrons, and photons to independently calculate the evolution of the chemical potentials of the electrons and positrons while computing the associated collision integrals at every time step. We find that the electron and positron chemical potentials deviate from the case with chemical equilibrium. While our results do not affect the interpretation of precision cosmological measurements in elucidating the standard cosmological model, these out of equilibrium effects may be important for testing physics beyond the standard model.

We discuss a new formalism for light propagation which can be used within the regime of validity of geometric optics, but with no limitation on the scales of interest: from inside the Galaxy to the ultralarge scales of cosmology. One of our main results is that within this framework it is possible to calculate all relevant observables (image magnification, parallax, position drift or proper motion) by simply differentiating the photon trajectory with respect to the initial data. We then focus on a new observable, which we name the distance slip: it is defined as the relative difference between the angular diameter distance and the parallax distance. Its peculiarity lies in the fact that its value is independent of the momentary motions of both the source and the observer and that for short distances it shows a tomographic property, being proportional to the amount of matter along the line of sight. After describing further its properties and methods of measurement, we specialize our study of the distance slip to cosmology. We show that it does not depend on the Hubble constant $H_0$ and that its dependence on the other cosmological parameters is different from other distance indicators. This suggests that the distance slip may contain new information.