We compute the one-loop effective action of the Hořava theory, in its nonprojectable formulation. We take the quantization of the ($2+1$)-dimensional theory in the Batalin-Fradkin-Vilkovisky formalism, and comment on the extension to the ($3+1$) case. The second-class constraints and the appropriate gauge-fixing condition are included in the quantization. The ghost fields associated with the second-class constraints can be used to get the integrated form of the effective action, which has the form of a Berezinian. We show that all irregular loops cancel between them in the effective action. The key for the cancellation is the role of the ghosts associated with the second-class constraints. These ghosts form irregular loops that enter in the denominator of the Berezinian, eliminating the irregular loops of the bosonic nonghost sector. Irregular loops produce dangerous divergences; hence their cancellation is an essential step for the consistency of the theory. The cancellation of this kind of divergences is in agreement with the previous analysis done on the ($2+1$) quantum canonical Lagrangian and its Feynman diagrams.

Emergent modified gravity presents a new set of generally covariant gravitational theories in which the space-time metric is not directly given by one of the fundamental fields. A metric compatible with the modified dynamics of gravity is instead derived from covariance conditions for space-time in canonical form. By staying within the canonical setting throughout all the required steps, several assumptions about space-time made implicitly in modified action principles can be relaxed. This paper presents a significant extension of existing vacuum models to the case of a scalar field coupled to emergent modified gravity in a spherically symmetric setting. Unlike in previous attempts for instance in models of loop quantum gravity, it is possible to maintain general covariance in the presence of modified gravity-scalar couplings. In general, however, the emergent space-time metric depends not only on the phase-space degrees of freedom of the gravitational part of the coupled theory, but also on the scalar field. Matter therefore directly and profoundly affects the geometry of space-time, not only through the well-known dynamical coupling of stress-energy to curvature as in Einstein’s equation, but even on a kinematical level before equations of motion are imposed. In addition to the covariance condition, this paper introduces further physical requirements that may be imposed in order to reduce modified gravity-scalar theories to more specific classes. In some cases, coupling emergent modified gravity to a scalar field eliminates some of the modifications that would be possible in a vacuum situation. Moreover, certain results about the removal of classical black hole singularities in vacuum emergent modified gravity are found to be unstable under the inclusion of matter fields. However, alternative modifications exist in which singularities are removed even in the presence of matter. Emergent modified gravity is seen to provide a large class of new scalar-tensor theories with second-order field equations.

Quantum fluctuations in spacetime can, in some cases, lead to distortion in astronomical images of faraway objects. In particular, a stochastic model of quantum gravity predicts an accumulated fluctuation in the path length $\mathrm{\Delta }L$ with variance $⟨\mathrm{\Delta }{L}^2⟩\sim l_{p}L$ over a distance $L$, similar to a random walk, and assuming no spatial correlation above length $l_p$; it has been argued that such an effect is ruled out by observation of sharp images from distant stars. However, in other theories, such as the pixellon [modeled on the Verlinde-Zurek (VZ) effect], quantum fluctuations can still accumulate as in the random walk model while simultaneously having large distance correlations in the fluctuations. Using renormalization by analytic continuation, we derive the correlation transverse to the light propagation, and show that image distortion effects in the pixellon model are strongly suppressed in comparison to the random walk model, thus evading all existing and future constraints. We also find that the diffraction of light rays does not lead to qualitative changes in the blurring effect.

Tuning into the bass notes of the large-scale structure requires careful attention to geometrical effects arising from wide angles. The spherical Fourier-Bessel (SFB) basis provides a harmonic-space coordinate system that fully accounts for all wide-angle effects. To demonstrate the feasibility of the SFB power spectrum, in this paper we validate our SFB pipeline by applying it to log-normal, and both complete and realistic EZmock simulations that were generated for eBOSS DR16 LRG sample. We include redshift space distortions and the local average effect (also known as integral constraint). The covariance matrix is obtained from 1000 EZmock simulations and inverted using eigenvalue decomposition.

In this work, we study the propagation and absorption of plasma waves in the context of the Maxwell-Carroll-Field-Jackiw (MCFJ) electrodynamics with a purely spacelike background playing the role of the anomalous Hall conductivity, concerning the anomalous Hall current. Such a current is also found in an axion field which increases linearly with a space coordinate. The Maxwell equations are rewritten for a cold, uniform, and collisionless fluid plasma model, allowing us to determine the new refractive indices and propagating modes. The analysis begins for propagation along the magnetic axis, examined in the cases of chiral vectors parallel and orthogonal to the magnetic field. Two distinct refractive indices (associated with right-handed circularly polarized [RCP] and left-handed circularly polarized [LCP] waves) are obtained and the associated propagation and absorption zones are determined. The low-frequency regime is discussed and we obtain RCP and LCP helicons. We scrutinize optical effects, such as birefringence and dichroism, and observe rotatory power sign reversion, a property of chiral MCFJ plasmas. We also examine the case of transversal propagation in the direction orthogonal to the magnetic field, providing much more involved results.

In the present paper, we consider processes involving the emission of soft photons in the presence of a strong laser field. We demonstrate that the matrix element $S$ for a process $\mathrm{i}\to \mathrm{f}+\gamma$, with a soft photon $\gamma$, can be expressed in terms of the matrix element $S_0$ for the process $\mathrm{i}\to \mathrm{f}$ through a simple multiplicative factor in the integrand over $\varphi$. This approximation enables a result that is exact in the phase and approximate in the prefactor to order $\mathcal{O}(\omega /{ϵ}_{\mathrm{char}})$, where $\omega$ is the frequency of the soft photon and ${ϵ}_{\mathrm{char}}$ is the characteristic energy of the $\mathrm{i}\to \mathrm{f}$ process. We demonstrate several important applications of this soft photon approximation. First, under soft photon approximation we compute the probabilities of nonlinear Compton scattering and photon emission in the superposition of a laser and atomic fields and compare obtained result with the exact one. Second, we demonstrate that the amplitude of $n$ soft photons emission has factorization, which corresponds to the independence of the emission of $n$ soft photons. Third, we use the discussed approximation to prove cancellation of real and virtual infrared divergences for nonlinear Compton scattering and derive the finite radiative corrections. The soft photon approximation is a useful tool for investigation of different QED processes in the presence of a strong laser field. Also, it can be widely used for computation of infrared part of radiative correction for some processes.

Due to rapidly improving quantum computing hardware, Hamiltonian simulations of relativistic lattice field theories have seen a resurgence of attention. This computational tool requires turning the formally infinite-dimensional Hilbert space of the full theory into a finite-dimensional one. For gauge theories, a widely used basis for the Hilbert space relies on the representations induced by the underlying gauge group, with a truncation that keeps only a set of the lowest dimensional representations. This works well at large bare gauge coupling, but becomes less efficient at small coupling, which is required for the continuum limit of the lattice theory. In this work, we develop a new basis suitable for the simulation of an SU(2) lattice gauge theory in the maximal tree gauge. In particular, we show how to perform a Hamiltonian truncation so that the eigenvalues of both the magnetic and electric gauge-fixed Hamiltonian are mostly preserved, which allows for this basis to be used at all values of the coupling. Little prior knowledge is assumed, so this may also be used as an introduction to the subject of Hamiltonian formulations of lattice gauge theories.

In this paper we parallel the construction of Tong of a gauge theory for shallow water, by writing a gauge theory for the Euler fluid in $2+1$ dimensions. We then extend it to a Euler fluid coupled to an electromagnetic background. We argue that the gauge theory formulation provides a topological argument for the quantization of $2+1$ dimensional Euler Hopfion solution. In the process, we find a (nongauge) action for the Euler fluid that can be extended to any dimension, including the physical $3+1$ dimensions. We also discuss several aspects of the Arnold-Beltrami-Childress flow.

We calculate the effective mass of gravitational perturbations induced by the interaction of the classical gravitational field with quantum matter in the background of the Poincaré patch of de Sitter space. Using the Schwinger-Keldysh diagrammatic technique, the one-loop effective action is calculated, and it is shown that the graviton does not acquire mass for the most symmetric Bunch-Davies state. However, we have shown that even in this case, there is a nontrivial modification of the theory at one loop in the scalar sector of gravity.

Gravitational waves can generate electromagnetic effects inside a strong electric or magnetic field within the Standard Model and general relativity. Here we propose using a quarterly split cavity and LC (inductor and capacitor) resonance circuit to detect a high-frequency gravitational wave from 0.1 MHz to GHz. We perform a full 3D simulation of the cavity’s signal for sensitivity estimate. Our sensitivity depends on the coherence timescale of the high-frequency gravitational wave sources and the volume size of the split cavity. We discuss the resonant measurement schemes for narrow-band gravitational wave sources and also a nonresonance scheme for broadband signals. For a meter-sized split cavity under a 14 Tesla magnetic field, the LC resonance enhanced sensitivity to the gravitational wave strain is expected to reach $h\sim {10}^{-20}$ around 10 MHz.

We study a symmetric teleparallel gravity with a Lagrangian of logarithmic form. The full model leads to an accelerated universe and for specific values of the free parameters the Hubble rate reduces to the well-known Dvali-Gabadadze-Porrati model, though the evolution of the gravitational potentials are different. We consider different branches of the logarithmic model, among which are self-accelerated branch and normal branch. The phenomenology of both the background and linear perturbations is discussed, including all the relevant effects on cosmic microwave background radiation (CMB) angular power spectrum, lensing and matter power spectra. To this purpose, we modified the Einstein-Boltzmann code mgcamb. Finally, we derive bounds on the free parameters which are in agreement with early dark energy constraint from CMB and big bang nucleosynthesis constraint on the helium abundance.

In this work, we analyze the observational properties of thin-shell gravastars under two astrophysical frameworks, namely surrounded by optically thin accretion disks and orbited by hot spots. We consider the thin-shell gravastar model with two free parameters, the gravastar radius and ratio of mass allocated at the thin-shell, and produce the corresponding observables via the use of numerical backwards ray-tracing codes. Regarding the observations of accretion disks, our results indicate that, due to the absence of a strong gravitational redshift effect, smooth gravastar configurations cannot reproduce shadow observations when internal emission is assumed. We thus expect such models to be excluded as candidates for supermassive objects in galactic cores. Nevertheless, thin-shell gravastars, with a large portion of their total mass allocated at the surface, can produce such an effect and are thus adequate candidates for black-hole mimickers. In the context of hot-spot orbits, the astrometrical observational properties of ultracompact gravastars resemble closely those of other ultracompact objects e.g. fluid stars and bosonic stars. However, for low-compacticity configurations, the time-integrated fluxes feature additional contributions in the form of a high-intensity plunge through image. These qualitative differences in the observational properties of gravastars in comparison with black-hole spacetimes could potentially be discriminated by the next generation of interferometric experiments in gravitational physics.

Emergent modified gravity presents a new class of gravitational theories in which the structure of space-time with Riemannian geometry of a certain signature is not presupposed. Relying on crucial features of a canonical formulation, the geometry of space-time is instead derived from the underlying dynamical equations for phase-space degrees of freedom together with a covariance condition. Here, a large class of spherically symmetric models is solved analytically for Schwarzschild-type black hole configurations with generic modification functions, using a variety of slicings that explicitly demonstrate general covariance. For some choices of the modification functions, a new type of signature change is found and evaluated. In contrast to previous versions discussed for instance in models of loop quantum gravity, signature change happens on timelike hypersurfaces in the exterior region of a black hole where it is not covered by a horizon. A large region between the horizon and the signature-change hypersurface may nevertheless be nearly classical, such that the presence of a signature-change boundary around Lorentzian space-time, or a Euclidean wall around the Universe, is consistent with observations provided signature change happens sufficiently far from the black hole.

We propose a new model to generate large anisotropies in the scalar-induced gravitational wave (SIGW) background via sound speed resonance in the inflaton-curvaton mixed scenario. Cosmological curvature perturbations are not only exponentially amplified at a resonant frequency, but also preserve significant non-Gaussianity of local type described by $f_{\mathrm{nl}}$. Besides a significant enhancement of energy-density fraction spectrum, large anisotropies in SIGWs can be generated, because of super-horizon modulations of the energy density due to existence of primordial non-Gaussianity. A reduced angular power spectrum ${\tilde{C}}_{\ell }$ could reach an amplitude of $[\ell (\ell +1){\tilde{C}}_{\ell }{]}^{1/2}\sim {10}^{-2}$, leading to potential measurements via planned gravitational-wave detectors such as DECIGO. The large anisotropies in SIGWs would serve as a powerful probe of the early Universe, shedding new light on the inflationary dynamics, primordial non-Gaussianity, and primordial black hole dark matter.

Approximations are commonly employed in realistic applications of scientific Bayesian inference, often due to convenience if not necessity. In the field of gravitational-wave (GW) data analysis, fast-to-evaluate but approximate waveform models of astrophysical GW signals are sometimes used in lieu of more accurate models to infer properties of a true GW signal buried within detector noise. In addition, a Fisher-information-based normal approximation to the posterior distribution can also be used to conduct inference in bulk, without the need for extensive numerical calculations such as Markov chain Monte Carlo simulations. Such approximations can generally lead to an inaccurate posterior distribution with poor statistical coverage of the true posterior. In this paper, we present a novel calibration procedure that calibrates the credible sets for a family of approximate posterior distributions, to ensure coverage of the true posterior at a level specified by the analyst. Tools such as autoencoders and artificial neural networks are used within our calibration model to compress the data (for efficiency) and to perform tasks such as logistic regression. As a proof of principle, we demonstrate our formalism on the GW signal from a high-mass binary black hole merger, a promising source for the near-future space-based GW observatory LISA.

The stochastic gravitational-wave background (SGWB) produced by merging neutron stars exhibits a peak in the kHz band. In this paper, we develop a theoretical framework to exploit this distinctive feature through a Markov Chain Monte Carlo analysis using a simulated dataset of SGWB measurements within this frequency range. The aim is to use the SGWB peak as an observable to constrain a set of astrophysical and cosmological parameters that accurately describe the sources of the SGWB. We examine how variations in these parameters impact the morphology of the SGWB and investigate the necessary sensitivity to effectively constrain them. Given our priors on astrophysical and cosmological parameters, and assuming a power-law integrated sensitivity curve of the order of ${10}^{-11}$ between 1 kHz and 5 kHz, we show that the values of the chirp mass and common envelope efficiency of the binary systems are retrieved with percent accuracy. Furthermore, the method allows for the reconstruction of the cosmological expansion history populated by these binaries, encompassing the Hubble constant, matter abundance, and the effective equation of state of dark energy.

In this paper, we study all transport coefficients of second-order dissipative fluid dynamics derived by V. E. Ambrus et al. [Phys. Rev. D 106, 076005 (2022)] from the relativistic Boltzmann equation in the relaxation-time approximation for the collision integral. These transport coefficients are computed for a classical ideal gas of massive particles, with and without taking into account the conservation of intrinsic quantum numbers. Through rigorous comparison between kinetic theory, second-order dissipative fluid dynamics, and leading-order anisotropic fluid dynamics for a ($0+1$)-dimensional boost-invariant flow scenario, we show that both fluid-dynamical theories describe the early far-from-equilibrium stage of the expansion reasonably well.

We use the diffusion Monte Carlo (DMC) method to calculate the doubly heavy tetraquark $T_{cc}$ system in two kinds of constituent quark models, the pure constituent quark model AL1/AP1 and the chiral constituent quark model. When the discrete configurations are complete and no spatial clustering is predetermined, the AL1/AP1 model gives an energy of $T_{cc}$ close to the $D{D}^{*}$ threshold, and the chiral constituent quark model yields a deeply bound state. We further calculate all doubly heavy tetraquark systems with $J^P=0^{+},1^{+},2^{+}$, and provide the binding energies of systems with bound states. The $I(J^P)=0(0^{+})$ $bc\overline{n}\overline{n}$, $0(1^{+})$ $bb\overline{n}\overline{n}$, $0(1^{+})$ $bc\overline{n}\overline{n}$, $\frac{1}{2}(1^{+})$ $bb\overline{s}\overline{n}$ systems have bound states in all three models. Since the DMC method has almost no restriction on the spatial part, the resulting bound states have greater binding energies than those obtained in previous works.

We introduce manifestly crossing-symmetric expansions for arbitrary systems of 1D CFT correlators. These expansions are given in terms of certain Polyakov blocks which we define and show how to compute efficiently. Equality of operator product expansion and Polyakov block expansions leads to sets of sum rules that any mixed correlator system must satisfy. The sum rules are diagonalized by correlators in tensor product theories of generalized free fields. We show that it is possible to do a change of a basis that diagonalizes instead mixed correlator systems involving elementary and composite operators in a single field theory. As an application, we find the first nontrivial examples of optimal bounds, saturated by the mixed correlator system $\varphi ,{\varphi }^2$ in the theory of a single generalized free field.

The recent observation of NGC 1068 by the IceCube Neutrino Observatory has opened a new window to neutrino physics with astrophysical baselines. In this paper, we propose a new method to probe the nature of neutrino masses using these observations. In particular, our method enables searching for signatures of pseudo-Dirac neutrinos with mass-squared differences that reach down to $\delta m^2\gtrsim {10}^{-21}{\mathrm{eV}}^2$, improving the reach of terrestrial experiments by more than a billion. Finally, we discuss how the discovery of a constellation of neutrino sources can further increase the sensitivity and cover a wider range of $\delta m^2$ values.