We study the dynamical generation of resonances in isospin singlet channels with mixing between two- and four-quark states. To this end, we generalize a Bethe-Salpeter approach to four-quark states employed previously to accommodate for mixing diagrams. The $q\overline{q}q\overline{q}$ and $q\overline{q}$ components of the Bethe-Salpeter wave function (with light quarks $q\in \{u,d\}$) are determined consistently in a symmetry-preserving truncation of the underlying Dyson-Schwinger equations. As a prominent example, we deal with the isospin-singlet $0^{++}$ meson with light quark content. We find that the $\pi \pi$ contribution of the four-quark component is mainly responsible for the low (real part of the) mass of the resulting state. We also study the analytic structure in the complex momentum plane and find a branch cut at the two-pion threshold and a singularity in the second Riemann sheet indicating a considerable decay width. Our findings are in excellent qualitative agreement with the general picture for the $\sigma /f_0(500)$ that emerged in the past two decades from dispersive approaches.

We propose an improved quark coalescence model for spin alignment of vector mesons and polarization of baryons by spin density matrix with phase space dependence. The spin density matrix is defined through Wigner functions. Within the model we propose an understanding of spin alignments of vector mesons $\varphi$ and $K^{*0}$ (including ${\overline{K}}^{*0}$) in the static limit: a large positive deviation of ${\rho }_{00}$ for $\varphi$ mesons from $1/3$ may come from the electric part of the vector $\varphi$ field, while a negative deviation of ${\rho }_{00}$ for $K^{*0}$ may come from the electric part of vorticity tensor fields. Such a negative contribution to ${\rho }_{00}$ for $K^{*0}$ mesons, in comparison with the same contribution to ${\rho }_{00}$ for $\varphi$ mesons which is less important, is amplified by a factor of the mass ratio of strange to light quark times the ratio of $⟨{\mathbf{p}}_b^2⟩$ on the wave function of $K^{*0}$ to $\varphi$ (${\mathbf{p}}_b$ is the relative momentum of two constituent quarks of $K^{*0}$ and $\varphi$). These results should be tested by a detailed and comprehensive simulation of vorticity tensor fields and vector meson fields in heavy ion collisions.

We address the precision of the estimation procedures for the minimum length arising from gravitational theories. In particular, we provide bounds on precision and assess the use of quantum probes to enhance the estimation performance. At first, we review the concept of minimum length and how it induces a perturbative term appearing in the Hamiltonian of any quantum system, which itself is proportional to a parameter depending on the minimum length. We then systematically study the effects of this perturbation on different state preparations and for several one-dimensional systems, and evaluate the quantum Fisher information in order to find the ultimate bounds to precision. Eventually, we investigate the role of dimensionality by analyzing the use of two-dimensional square well and harmonic oscillator systems to probe the minimal length. Our results show that quantum probes are convenient resources, providing potential enhancement in precision. Additionally, our results provide a set of guidelines to design future experiments to detect the minimum length.

The effect of conserved baryon, isospin, and strangeness charges on the behavior of phase transitions in dense matter is studied. Baryonic matter is described within the three-flavor Polyakov–Nambu–Jona-Lasinio model and several charge fractions $Y_Q$ are considered. The role of the vector interaction, which can be important to describe dense systems, is discussed. Special attention is given to the case with charge fraction $Y_Q=0.4$, due to its importance in heavy-ion collisions and core-collapse supernova matter. It is shown that the possible formation of chiral-symmetric quark matter in the laboratory will be favored in asymmetric matter. Besides, the inclusion of the vector interaction reinforces the formation of quark matter at lower densities.

We explore the prospects to discover the $h\to Z\gamma$ decay in $t\overline{t}$-associated production, featuring a signal-to-background ratio of $\mathcal{O}(1)$. Performing a detailed analysis of the semileptonic $t\overline{t}$-decay channel, we demonstrate that the production mode could lead to a $\sim 5\sigma$ discovery at the high-luminosity LHC, while the effective $hZ\gamma$ coupling could be extracted with a $\sim 15\%$ accuracy. Extending the analysis to potential future $pp$ colliders with 27 TeV and 100 TeV center-of-mass energies, we also show that the latter would allow precision measurements at the few percent level, rendering possible precise extractions of the spin and $CP$ properties of the Higgs boson.

According to the Ryu-Takayanagi prescription, the entanglement entropy of subsystems in the boundary conformal field theory (CFT) is proportional to the area of extremal surfaces in bulk asymptotically anti-de Sitter (AdS) spacetimes. The flat-space limit of these surfaces is not well defined in the generic case. We introduce a new curve in the three-dimensional asymptotically AdS spacetimes with a well-defined flat-space limit. We find this curve by using a new vector, which is vanishing on it and is normal to the bulk modular flow of the original interval in the two-dimensional CFT. The flat-space limit of this new vector is well defined and gives rise to the bulk modular flow of the corresponding asymptotically flat spacetime. Moreover, after Rindler transformation, this new vector is the normal Killing vector of the inner horizon of the Bañados-Teitelboim-Zanelli black hole. We reproduce all known results about the holographic entanglement entropy of Bondi-Metzner-Sachs invariant field theories, which are dual to the asymptotically flat spacetimes.

We propose a microscopic quantum description for Hawking radiation as Andreev reflections, which resolves the quantum information paradox at black hole event horizons. The detailed microscopic analysis presented here reveals how a black hole, treated as an Andreev reflecting mirror, provides a manifestly unitary description of an evaporating black hole, expanding our previous analysis presented in [S. K. Manikandan and A. N. Jordan, Phys. Rev. D 96, 124011 (2017), S. K. Manikandan and A. N. Jordan, Phys. Rev. D 98, 124043 (2018)]. In our analogy, a black hole resolves the information paradox by accepting particles—pairing them with the infalling Hawking quanta into a Bardeen-Cooper-Schrieffer (BCS) like quantum ground state—while Andreev reflects the quantum information as encoded in outgoing Hawking radiation. The present approach goes beyond the black hole final state proposal by Horowitz and Maldacena [J. High Energy Phys. 02 (2004) 008] by providing necessary microscopic details which allows us to circumvent important shortcomings of the black hole final state proposal. We also generalize the present Hamiltonian description to make an analogy to the apparent loss of quantum information possible in an Einstein-Rosen bridge via crossed Andreev reflections.

Galaxy-galaxy strong gravitational lenses have become a popular probe of dark matter (DM) by providing a window into structure formation on the smallest scales. In particular, the convergence power spectrum of subhalos within lensing galaxies has been suggested as a promising observable to study DM. However, the distances involved in strong-lensing systems are vast, and we expect the relevant volume to contain line-of-sight (LOS) halos that are not associated with the main lens. We develop a formalism to calculate the effect of LOS halos as an effective convergence power spectrum. The multilens plane equation couples the angular deflections of consecutive lens planes, but by assuming that the perturbations due to the LOS halos are small, we show that they can be projected onto the main-lens plane as effective subhalos. We test our formalism by simulating lensing systems using the full multiplane lens equation and find excellent agreement. We show how the relative contribution of LOS halos and subhalos depends on the source and lens redshift, as well as the assumed halo and subhalo mass functions. For a fiducial system with fraction of DM halo mass in substructure $f_{\mathrm{sub}}=0.4\%$ for subhalo masses $[{10}^5–{10}^8]{\mathrm{M}}_{\odot }$, the interloper contribution to the power spectrum is at least several times greater than that of subhalos for source redshifts $z_s\gtrsim 0.5$. Furthermore, it is likely that for the SLACS and BELLS lenses the interloper contribution dominates: $f_{\mathrm{sub}}\gtrsim 2\%$ (4%) is needed for subhalos to dominate in SLACS (BELLS), which is higher than current upper bounds on $f_{\mathrm{sub}}$ for our mass range. Since the halo mass function is better understood from first principles, the dominance of interlopers in galaxy-galaxy lenses with high-quality imaging can be seen as a significant advantage when translating this observable into a constraint on DM.

The possibility of antihelium production in interaction of cosmic rays with the interstellar gas is studied using large-scale Monte Carlo simulations. For this purpose, an energy-dependent coalescence mechanism developed previously is extended to estimate the production of light antinuclei (${}^3\overline{\mathrm{He}}$ and ${}^4\overline{\mathrm{He}}$). The uncertainty in the coalescence parameter and its effect on the expected antiparticle flux is also investigated. The simulated background antihelium fluxes are found to be lower than the fluxes predicted by simplified models using numerical scaling techniques.

On June 20, 2020, the LIGO-Virgo collaboration announced the discovery of GW190814, a gravitational wave event originating from a binary system merger between a black hole of mass $M_1={23.2}_{-1.0}^{+1.1}{M}_{\odot }$ and an unidentified object with a mass of $M_2=2.59_{-0.09}^{+0.08}{M}_{\odot }$. This second object would be either the heaviest neutron star or lightest black hole observed to date. Here we investigate the possibility of the $\sim 2.6M_{\odot }$ object being a primordial black hole (PBH). We find that a primordial black hole explanation to GW190814 is unlikely as it is limited by the formation rate of the primary stellar progenitor and the time available for a pair of primordial- and stellar-origin black hole binaries to form and merge within a hubble time.

Results are presented from numerical simulations of the flat-space nonlinear Maxwell-Klein-Gordon equations demonstrating deep inelastic scattering of $m=1$ vortices for a range of Ginzburg-Landau (or Abelian-Higgs) parameters ($\kappa$), impact parameters ($b$), and initial velocities ($v_0$). The threshold ($v_0^{*}$) of right-angle scattering is explored for head-on ($b=0$) collisions by varying $v_0$. Solutions obey time-scaling laws, $T\propto \alpha \ln (v_0-v_0^{*})$, with $\kappa$-dependent scaling exponents, $\alpha$, and have $v_0^{*}$ that appear not to have the previously reported upper bound. The arbitrarily long-lived static intermediate attractor at criticality ($v_0=v_0^{*}$) is observed to be the $\kappa$-specific $m=2$ vortex solution. Scattering angles are observed for off-axis ($b\ne 0$) collisions for a wide range of $b$, $v_0$, and $\kappa$. It is shown that for arbitrarily small impact parameters ($b\to 0$), the unstable $\kappa$-dependent $m=2$ “critical” vortex is an intermediate attractor and decays with a $\kappa$-independent scattering angle of 135°, as opposed to either of the well-known values of 180° or 90° for $b=0$.

We study the $O(N)$ model in dimension three ($3d$) at large and infinite $N$ and show that the line of fixed points found at $N=\infty$—the Bardeen-Moshe-Bander (BMB) line—has an intriguing origin at finite $N$. The large $N$ limit that allows us to find the BMB line must be taken on particular trajectories in the $(d,N)$ plane: $d=3-\alpha /N$ and not at fixed dimension $d=3$. Our study also reveals that the known BMB line is only half of the true line of fixed points, the second half being made of singular fixed points. The potentials of these singular fixed points show a cusp for a finite value of the field and their finite $N$ counterparts a boundary layer.

In this paper, we investigate linear instabilities of hydrodynamics with corrections up to first order in derivatives. It has long been known that relativistic (Lorentzian) first order hydrodynamics, with positive local entropy production, exhibits unphysical instabilities. We extend this analysis to fluids with Galilean and Carrollian boost symmetries. We find that the instabilities occur in all cases, except for fluids with Galilean boost symmetry combined with the choice of macroscopic variables called Eckart frame. We also present a complete linearized analysis of the full spectrum of first order Carrollian hydrodynamics. Furthermore, we show that even in a fluid without boost symmetry present, instabilities can occur. These results provide evidence that the unphysical instabilities are symptoms of first order hydrodynamics, rather than a special feature of Lorentzian fluids.

We argue a smallness of gauge couplings in Abelian quiver gauge theories, taking the anomaly cancellation condition into account. In theories of our interest there exist chiral fermions leading to chiral gauge anomalies, and an anomaly-free gauge coupling tends to be small, and hence can give a nontrivial condition of the weak gravity conjecture. As concrete examples, we consider $U(1{)}^k$ gauge theories with a discrete symmetry associated with cyclic permutations between the gauge groups, and identify anomaly-free $U(1)$ gauge symmetries and the corresponding gauge couplings. Owing to this discrete symmetry, we can systematically study the models and we find that the models would be examples of the weak coupling conjecture. It is conjectured that a certain class of chiral gauge theories with too many $U(1)$ symmetries may be in the swampland. We also numerically study constraints on the couplings from the scalar weak gravity conjecture in a concrete model. These constraints may have a phenomenological implication to model building of a chiral hidden sector as well as the visible sector.

The final fate of gravitational collapse of massive stars has been a subject of interest for a long time since such a collapse may lead to black holes and naked singularities alike. Since, the formation of naked singularities is forbidden by the cosmic censorship conjecture, exploring their observational differences from black holes may be a possible avenue to search for these exotic objects. The simplest possible naked singularity spacetime emerges from the Einstein massless scalar field theory with the advantage that it smoothly translates to the Schwarzschild solution by the variation of the scalar charge. This background, known as the Janis-Newman-Winicour spacetime is the subject of interest in this work. We explore electromagnetic observations around this metric which involves investigating the characteristics of black hole accretion and shadow. We compute the shadow radius in this spacetime and compare it with the image of M87*, recently released by the Event Horizon Telescope Collaboration. Similarly, we derive the expression for the luminosity from the accretion disk and compare it with the observed optical luminosity of eleven Palomar Green quasars. Our analysis indicates that the shadow of M87* and the quasar optical data consistently favor the Schwarzschild background over the Janis-Newman-Winicour spacetime. The implications of this result are discussed.

We describe a set of time evolution equations and its numerical implementation for the investigation of non-axisymmetric oscillations of rapidly rotating compact objects in full general relativity, taking into account the contribution of a dynamic spacetime. We derive the perturbation equations for the spacetime in the Hilbert gauge, while the hydrodynamical evolution is based on perturbations of the energy-momentum tensor. In our numerical implementation, we use Kreiss-Oliger dissipation in order to achieve a stable time evolution. Our code features high accuracy at comparably low computational expense and we are able to extract the frequencies of nonaxisymmetric modes of compact objects with rotation rates up to the Kepler limit.

In the literature on $f(\mathbb{T})$ gravity, the status of local Lorentz invariance and the number of physical degrees of freedom have been controversial issues. Relying on a detailed Hamiltonian analysis, we show that local Lorentz invariance is completely broken, whereas, generically, the number of physical degrees of freedom is $N^{*}=5$; in $D$ dimensions, this number is $N^{*}=D(D-3)/2+(D-1)$. As expected, the theory is vulnerable to having problematical propagating modes. We compare our results with those existing in the literature. As a by-product of our analysis, the diffeomorphism invariance is explicitly confirmed.

The natural constraints for the weak-field approximation to composite gravity, which is obtained by expressing the gauge vector fields of the Yang-Mills theory based on the Lorentz group in terms of tetrad variables and their derivatives, are analyzed in detail within a canonical Hamiltonian approach. Although this higher derivative theory involves a large number of fields, only a few degrees of freedom are left, which are recognized as selected stable solutions of the underlying Yang-Mills theory. The constraint structure suggests a consistent double coupling of matter to both Yang-Mills and tetrad fields, which results in a selection among the solutions of the Yang-Mills theory in the presence of properly chosen conserved currents. Scalar and tensorial coupling mechanisms are proposed, where the latter mechanism essentially reproduces linearized general relativity. In the weak-field approximation, geodesic particle motion in static isotropic gravitational fields is found for both coupling mechanisms. An important issue is the proper Lorentz covariant criterion for choosing a background Minkowski system for the composite theory of gravity.

We study the quasiperiodic oscillations from the accretion disk around the distorted Schwarzschild black hole in the framework of the resonant models. We confine ourselves to the case of a quadrupole distortion which can be caused for example by the accreting matter flow in the vicinity of the compact object. For the purpose we examine the linear stability of the circular geodesic orbits in the equatorial plane and derive analytical expressions for the radial and vertical epicyclic frequencies. We investigate their properties in comparison with the isolated Schwarzschild black hole. Due to the influence of the external matter the vertical epicyclic frequency is not always positive anymore, and the stability of the circular orbits is determined by the interplay between both of the frequencies. As a result, the stable circular orbits do not extend to infinity, but are confined to a finite annular region between an inner and an outer marginally stable orbit. In addition, the degeneracy between the vertical epicyclic and the orbital frequency, which is characteristic for the Schwarzschild solution, is broken, and there are regions in the parametric space where the radial epicyclic frequency is larger than the vertical one. All these properties allow for much more diverse types of nonlinear resonances to be excited than for the isolated Schwarzschild black hole, which can provide an explanation for the observed $3:2$ ratio between the twin-peak frequencies of the quasiperiodic oscillations from the accretion disk.

We construct novel solutions to the effective Einstein equation with four dimensional cosmological constant on a 3-brane in Randall-Sundrum II scenario. The charged solution is obtained by assuming the existence of localized Maxwell fields on the 3-brane. Timelike and null circular geodesics in the neutral rotating braneworld spacetime with Newman-Unti-Tamburino parameter are discussed, and we find that such geodesics cannot occur on the equatorial plane. On nonequatorial planes, timelike circular geodesics can occur for the negative tidal charge, but we cannot find numerical results to support the existence of nonequatorial null circular geodesics.