New solutions of relativistic wave equations are obtained in a unified manner from generating functions of spinorial variables. The choice of generating functions as Gaussians leads to representations in the form of generalized fractional Fourier transforms. Wave functions satisfying the Dirac, Maxwell, and Weyl equations are constructed by simple differentiations with respect to spinorial arguments. In the simplest case, one obtains Maxwell and Dirac hopfion solutions.

We use the $3+1$ formalism of numerical relativity to investigate the robustness of Starobinsky and Higgs inflation to inhomogeneous initial conditions, in the form of either a field gradient or kinetic energy density. Sub-Hubble and Hubble-sized fluctuations generically lead to inflation after an oscillatory phase between gradient and kinetic energies. Hubble-sized inhomogeneities also produce contracting regions that end up forming primordial black holes, subsequently diluted by inflation. We analyze the dynamics of the preinflation era and the generation of vector and tensor fluctuations. Our analysis further supports the robustness of inflation to any size of inhomogeneity in the field, velocity, or equation of state. At large field values, the preinflation dynamics only marginally depends on the field potential and it is expected that such behavior is universal and applies to any plateau-type inflation potential, which is favored by cosmic microwave background observations from Planck.

Gravitational waves emitted by neutron star black hole mergers encode key properties of neutron stars—such as their size, maximum mass, and spins—and black holes. However, it is challenging to generate accurate waveforms from these systems with numerical relativity, and not much is known about systematic uncertainties due to waveform modeling. We simulate gravitational waves from neutron star black hole mergers by hybridizing numerical relativity waveforms produced with the SpEC code with a recent numerical relativity surrogate NRHybSur3dq8Tidal. These signals are analyzed using a range of available waveform families, and statistical and systematic errors are reported. We find that at a network signal-to-noise ratio (SNR) of 30, statistical uncertainties are usually larger than systematic offsets, while at an SNR of 70, the two become comparable. The individual black hole and neutron star masses, as well as the mass ratios, are typically measured very precisely, though not always accurately at high SNR. At an SNR of 30, the neutron star tidal deformability can only be bound from above, while for louder sources, it may be measured and constrained away from zero. All neutron stars in our simulations are nonspinning, but in no case can we constrain the neutron star spin to be smaller than $\sim 0.4$ (90% credible interval). At lower mass ratios, waveform families whose late inspiral has been tuned specifically for neutron star black hole signals typically yield the most accurate characterization of the source parameters. Their measurements are in tension with those obtained using waveform families tuned against binary neutron stars, even for mass ratios that could be relevant for both binary neutron stars and neutron star black holes mergers. At higher mass ratios, waveforms that account for higher order modes yield the best results.

We construct analytic ($3+1$)-dimensional inhomogeneous and topologically nontrivial pion systems using chiral perturbation theory. We discuss the effect of isospin asymmetry with vanishing electromagnetic interactions as well as some particular configurations with nonvanishing electromagnetic interactions. The inhomogeneous configurations of the pion fields are characterized by a nonvanishing topological charge that can be identified with baryons surrounded by a cloud of pions. This system supports a topologically protected persistent superflow. When the electromagnetic field is turned on the superflow corresponds to an electromagnetic supercurrent.

We investigate how physical quantities associated with relativistic stars in the Jordan and Einstein frames are related by the generalized disformal transformations constructed by the scalar and vector fields within the slow-rotation approximation. We consider the most general scalar disformal transformation constructed by the scalar field, and by the vector field without and with the $U(1)$ gauge symmetry, respectively. At the zeroth order of the slow-rotation approximation, by imposing that both the metrics of the Jordan and Einstein frames are asymptotically flat, we show that the Arnowitt-Deser-Misner mass is frame invariant. At the first order of the slow-rotation approximation, we discuss the disformal transformations of the frame-dragging function, angular velocity, angular momentum, and moment of inertia of the star. We show that the angular velocity of the star is frame invariant in all the cases. While the angular momentum and moment of inertia are invariant under the scalar disformal transformation, they are not under the vector disformal transformation without and with the $U(1)$ gauge symmetry.

The analysis of gravitational wave (GW) data from advanced LIGO provides the mass of each companion of binary black holes as the source of GWs. The mass of events corresponding to the binary black holes from GW is above $20M_{\odot }$ which is much larger than the mass of astrophysical black holes detected by x-ray observations. In this work, we examine primordial black holes (PBHs) as the source of LIGO events. Assuming that 100% of the dark matter is made of PBHs, we estimate the rate at which these objects make binaries, merge, and produce GWs as a function of the redshift. The gravitational lensing of GWs by PBHs can also enhance the amplitude of the strain. We simulate GWs sourced by binary PBHs, with the detection threshold of $S/N>10$ for both Livingston and Hanford detectors. For the log-normal mass function of PBHs, we generate the expected distribution of events, compare our results with the observed events, and find the best value of the mass function parameters (i.e., $M_c=25M_{\odot }$ and $\sigma =0.6$) in the log-normal mass function. Comparing the expected number of events with the number of observed ones rules out the present-Universe binary formation PBH scenario as the candidate for the source of GW events detected by LIGO.

Acoustic holes are the hydrodynamic analog of standard black holes. Featuring an acoustic horizon, these systems spontaneously emit phonons at the Hawking temperature. We derive the Hawking temperature of the acoustic horizon by fully exploiting the analogy between black and acoustic holes within a covariant kinetic theory approach. After deriving the phonon distribution function from the covariant kinetic equations, we reproduce the expression of the Hawking temperature by equating the entropy and energy losses of the acoustic horizon and the entropy and energy gains of the spontaneously emitted phonons. Differently from previous calculations we do not need a microscopical treatment of normal mode propagation. Our approach opens a different perspective on the meaning of Hawking temperature and its connection with entropy, which may allow an easier study of nonstationary horizons beyond thermodynamic equilibrium, including dissipative effects.

Correlation functions can be described by the corresponding equations, viz., the gap equation for the quark propagator and the inhomogeneous Bethe-Salpeter equation for the vector dressed-fermion-Abelian-gauge-boson vertex in which specific truncations have to be implemented. The general vector and axial-vector Ward-Green-Takahashi identities require these correlation functions to be interconnected; in consequence of this, truncations made must be controlled consistently. It turns out that, if the rainbow approximation is assumed in the gap equation, the scattering kernel in the Bethe-Salpeter equation can adopt the ladder approximation, which is one of the most basic attempts to truncate the scattering kernel. Additionally, a modified-ladder approximation is also found to be a possible symmetry-preserving truncation scheme. As an illustration of this approximation for application, a treatment of the pion is included. The pion mass and decay constant are found to be degenerate in ladder and modified-ladder approximations, even though the Bethe-Salpeter amplitudes are with apparent distinction. The justification for the modified-ladder approximation is examined with the help of the Gell-Mann-Oakes-Renner relation.

Numerous experimental and theoretical results in liquids and plasmas suggest the presence of a critical momentum at which the shear diffusion mode collides with a nonhydrodynamic relaxation mode, giving rise to propagating shear waves. This phenomenon, labeled “k-gap,” could explain the surprising identification of a low-frequency elastic behavior in confined liquids. More recently, a formal study of the perturbative hydrodynamic expansion showed that critical points in complex space, such as the aforementioned k-gap, determine the radius of convergence of linear hydrodynamics—its regime of applicability. In this work, we combine the two new concepts, and we study the radius of convergence of linear hydrodynamics in “real liquids” by using several data from simulations and experiments. We generically show that the radius of convergence increases with temperature and it surprisingly decreases with the electromagnetic interactions coupling. More importantly, for all the systems considered, we find that such a radius is set by the Wigner–Seitz radius—the characteristic interatomic distance of the liquid, which provides a natural microscopic bound.

It has recently been proved that, in the presence of vortex flows, the fluctuation dynamics of a rotating photon-fluid model is governed by the Klein-Gordon equation of an effective massive scalar field in a ($2+1$)-dimensional acoustic black-hole spacetime. Interestingly, it has been demonstrated numerically that the rotating acoustic black hole, like the familiar Kerr black-hole spacetime, may support spatially regular stationary density fluctuations (linearized acoustic scalar “clouds”) in its exterior regions. In particular, it has been shown that the composed rotating acoustic black-hole-stationary-scalar-field configurations of the photon-fluid model exist in the narrow dimensionless regime $\alpha \equiv {\mathrm{\Omega }}_0/m{\mathrm{\Omega }}_{\mathrm{H}}\in (1,{\alpha }_{\max })$ with ${\alpha }_{\max }\simeq 1.08$ (here ${\mathrm{\Omega }}_{\mathrm{H}}$ is the angular velocity of the black-hole horizon and $\{{\mathrm{\Omega }}_0,m\}$ are the effective proper mass and the azimuthal harmonic index of the acoustic scalar field, respectively). In the present paper, we use analytical techniques in order to explore the physical and mathematical properties of the acoustic scalar clouds of the photon-fluid model in the regime ${\mathrm{\Omega }}_{\mathrm{H}}{r}_{\mathrm{H}}\gg 1$ of rapidly spinning central supporting acoustic black holes. In particular, we derive a remarkably compact analytical formula for the discrete resonance spectrum $\{{\mathrm{\Omega }}_0({\mathrm{\Omega }}_{\mathrm{H}},m;n)\}$ which characterizes the stationary bound-state acoustic scalar clouds of the photon-fluid model. Interestingly, it is proved that the critical (maximal) mass parameter ${\alpha }_{\max }$, which determines the regime of existence of the composed acoustic black-hole-stationary-bound-state-massive-scalar-field configurations, is given by the exact dimensionless relation ${\alpha }_{\max }=\sqrt{\frac{32}{27}}$.

We investigate the electromagnetic form factor $F(q^2)$ of the meson by using the solvable ${\varphi }^3$ scalar field model in ($1+1$) dimensions. As the transverse rotations are absent in ($1+1$) dimensions, the advantage of the light-front dynamics (LFD) with the light-front time $x^{+}=x^0+x^3$ as the evolution parameter is maximized in contrast to the usual instant form dynamics (IFD) with the ordinary time $x^0$ as the evolution parameter. In LFD, the individual $x^{+}$-ordered amplitudes contributing to $F(q^2)$ are invariant under the boost, i.e., frame independent, while the individual $x^0$-ordered amplitudes in IFD are not invariant under the boost but dependent on the reference frame. The LFD allows us to get the analytic result for the one-loop triangle diagram which covers not only the spacelike ($q^2<0$) but also timelike ($q^2>0$) region. Using the analytic results, we verify that the real and imaginary parts of the form factor satisfy the dispersion relations in the entire $q^2$ space. Comparing with the results in ($3+1$) dimensions, we discuss the transverse momentum effects on $F(q^2)$. We also discuss the longitudinal charge density in terms of the boost-invariant variable $\tilde{z}=p^{+}{x}^{-}$ in LFD.

We propose a two component dark matter setup by extending the Standard Model with a singlet and a hyperchargeless triplet scalars, each of them being odd under different $Z_2$ symmetries. We observe that the interconversion between the two dark matter components allow a viable parameter space where masses of both the dark matter candidates can be below TeV, even though their individual contribution to single component dark matter rules out any such sub-TeV dark matter. We find that a lighter mass of the neutral component of the scalar triplet, playing the role of one dark matter component, compared to the singlet one is favored. In addition, the setup is shown to make the electroweak vacuum absolutely stable till the Planck scale, thanks to Higgs portal coupling with the scalar dark matter components.

We investigate analog black holes generated in an array of direct current superconducting quantum interference devices (dc SQUIDs) coupled in parallel with a one-dimensional chain of single-domain nanomagnets. Magnetic solitons in the chain provide magnetic fields perpendicular to the SQUID array. This leads to the spatially varying velocities of electromagnetic waves through the nonlinear inductance in the array required for creating effective event horizons, resulting in analog black holes. We derive the Hawking temperature in this analog black hole based on the tunneling mechanism for Hawking radiation. The formula reflecting the soliton properties shows that Hawking radiation is observable using the current state-of-the-art technologies.

String theory predicts that the couplings of nature descend from dynamical fields. All known string-motivated particle physics models also come with a wide range of possible extra sectors. It is common to posit that such moduli are frozen to a background value, and that extra sectors can be nearly completely decoupled. Performing a partial trace over all sectors other than the visible sector generically puts the visible sector in a mixed state, with coupling constants drawn from a quantum statistical ensemble. An observable consequence of this entanglement between visible and extra sectors is that the reported values of couplings will appear to have an irreducible variance. Including this variance in fits to experimental data gives an important additional parameter that can be used to distinguish this scenario from the case where couplings are treated as fixed parameters. There is a consequent interplay between energy range and precision of an experiment that allows an extended reach for new physics.

We compute the $O(1/N^3)$ correction to the critical exponent $\eta$ in the chiral XY or chiral Gross-Neveu model in $d$-dimensions. As the leading order vertex anomalous dimension vanishes, the direct application of the large $N$ conformal bootstrap formalism is not immediately possible. To circumvent this we consider the more general Nambu-Jona-Lasinio model for a general non-Abelian Lie group. Taking the Abelian limit of the exponents of this model produces those of the chiral XY model. Subsequently we provide improved estimates for $\eta$ in the three-dimensional chiral XY model for various values of $N$.

In the analysis of neutron-antineutron oscillations, it has recently been argued in the literature that the use of the $i{\gamma }^0$ parity $n^p(t,-\overrightarrow{x})=i{\gamma }^{0}n(t,-\overrightarrow{x})$, which is consistent with the Majorana condition, is mandatory and that the ordinary parity transformation of the neutron field $n^p(t,-\overrightarrow{x})={\gamma }^{0}n(t,-\overrightarrow{x})$ has difficulties. We show that a careful treatment of the ordinary parity transformation of the neutron works in the analysis of neutron-antineutron oscillations. Technically, $CP$ symmetry in a mass diagonalization procedure is important and the two parity transformations $i{\gamma }_0$-parity and ${\gamma }_0$-parity are compensated for by the Pauli-Gürsey transformation. Our analysis shows that either choice of parity gives the correct results for neutron-antineutron oscillations if carefully treated.

We derive universal properties of the near-horizon geometry of spherically symmetric black holes that follow from the observability of a regular apparent horizon. Only two types of solutions are admissible. After reviewing their properties we show that only a special form of the solutions of the second type is consistent. We describe how these results extend to modified theories of gravity, including Einstein–Cartan theories. Then we describe the unique black hole formation scenario that necessarily involves both types of solutions. The generalized surface gravity is infinite at the apparent horizon. This feature and comparison of the required energy and timescales with the known semiclassical results suggest that the observed astrophysical black holes are horizonless ultra-compact objects, and the presence of a horizon is associated with currently unknown physics.

We study further a general-relativistic mechanism for the acquisition of tidal energy by free test particles near a gravitationally collapsed configuration. Specifically, we investigate the solutions of the timelike geodesic equation in a Fermi normal coordinate system established about the world line of an accelerated observer that remains spatially at rest in the exterior Schwarzschild spacetime. Such static observers in effect define the rest frame of the collapsed source. The gain in tidal energy is due to local spacetime curvature. Previous work in this direction in connection with astrophysical jets involved geodesic motion along the Kerr rotation axis where outward-moving particles could be tidally accelerated to almost the speed of light if their initial speed, as measured by the reference observer, is above a certain threshold escape velocity. We focus here for simplicity on the exterior Schwarzschild spacetime and show that the effective tidal acceleration to near the speed of light can occur for geodesic motion in certain radially outward directions. The implications of these results for the physics of gravitationally collapsed systems are briefly discussed.

We hereby derive the Newtonian metric potentials for the fourth-derivative gravity including the one-loop logarithm quantum corrections. It is explicitly shown that the behavior of the modified Newtonian potential near the origin is improved respect to the classical one, but this is not enough to remove the curvature singularity in $r=0$. Our result is grounded on a rigorous proof based on numerical and analytic computations.

We study the Maxwell quasinormal spectrum on asymptotically anti–de Sitter black holes with a set of two Robin type boundary conditions, by requiring the energy flux to vanish at asymptotic infinity. Focusing, for illustrative purposes, on Schwarzschild–anti–de Sitter black holes both without and with a global monopole, we unveil that, on the one hand, the Maxwell quasinormal spectrum bifurcates as the black hole radius increases for both boundary conditions, which is termed the mode split effect; while on the other hand, with an appropriate fixed black hole radius but increasing the monopole parameter, the first (second) boundary condition may trigger (terminate) the mode split effect.