The heavy hadron spectrum is constrained by symmetries, of which two of the most important ones are heavy-quark spin and SU(3)-flavor symmetries. Here we argue that in the molecular picture the $Y(4230)$ [or $Y(4260)$], the $Y(4360)$, and the recently discovered $Y(4500)$ and $Y(4620)$ vectorlike resonances are linked by these two symmetries. By formulating a contact-range effective field theory for the $D{\overline{D}}_1$ and $D_s{\overline{D}}_{s1}$ family of $S$- and $P$-wave charmed meson-antimeson systems, we find that if the $Y(4230)$ were to be a pure $D{\overline{D}}_1$ molecular state, there would be a $D^{*}{\overline{D}}_1$ partner with a mass similar to the $Y(4360)$, a $D_s{\overline{D}}_{s1}$ partner with a mass close to the $Y(4500)$, and three $J=1$, 2 $D_s^{*}{\overline{D}}_{s1}$ and $J=3$ $D_s^{*}{\overline{D}}_{s2}^{*}$ bound states with a mass in the vicinity of 4630 MeV, of which the first one ($J=1$) might correspond with the $Y(4620)$. The previous predictions can in turn be improved by modifying the assumptions we have used to build the effective field theory. In particular, if we consider the closeness of the $D^{*}{\overline{D}}_1\text{−}{D}^{*}{\overline{D}}_2^{*}$ and $D_s^{*}{\overline{D}}_{s1}\text{−}{D}_s^{*}{\overline{D}}_{s2}^{*}$ thresholds and include the related coupled channel dynamics, we predict a $J=2$ positive $C$-parity state with a mass around 4650 MeV. This hidden-strange and hidden-charm state might in turn be identified with the $X(4630)$ that has been discovered during the past year by the LHCb in the $J/\psi \varphi$ invariant mass distribution.

Spacetime variation of fundamental physical constants in an expanding Universe is predicted by a number of popular models. The masses of second-generation quarks are larger than first-generation quark masses by several orders of magnitude; therefore, spacetime variation in quark masses may significantly vary between each generation. We evaluate limits on variation in the $s$ and $c$ quark masses from big bang nucleosynthesis, Oklo natural nuclear reactor, ${\mathrm{Yb}}^{+}$, Cs, and Rb clock data. The construction of a ${}^{229}\mathrm{Th}$ nuclear clock is expected to enhance these limits by several orders of magnitude. Furthermore, constraints are obtained on an oscillating scalar or pseudoscalar cold dark matter field, as interactions of the field with quarks produce variations in quark masses.

We employ the domain wall fermion (DWF) formulation of the Thirring model on a lattice in $2+1+1$ dimensions and perform $N=1$ flavor Monte Carlo simulations. At a critical interaction strength the model features a spontaneous $\mathrm{U}(2)\to \mathrm{U}(1)\otimes \mathrm{U}(1)$ symmetry breaking; we analyze the induced spin-0 mesons, both Goldstone and non-Goldstone, as well as the correlator of the fermion quasiparticles, in both resulting phases. Crucially, we determine the anomalous dimension ${\eta }_{\psi }\approx 3$ at the critical point, in stark contrast with the Gross-Neveu model in 3D and with results obtained with staggered fermions. Our numerical simulations are complemented by an analytical treatment of the free fermion correlator, which exhibits large early-time artifacts due to branch cuts in the propagator stemming from unbound interactions of the fermion with its heavy doublers. These artifacts are generalizable beyond the Thirring model, being an intrinsic property of DWF, or more generally Ginsparg-Wilson fermions.

We study the drag and diffusion coefficients of the charm quark in the deconfined matter produced in the ultrarelativistic collisions by taking the color string percolation model (CSPM) approach. CSPM, being a QCD-inspired model, can give us essential information about the hot and dense system produced in ultrarelativistic collisions. With information on the initial percolation temperature and percolation density, we estimate the relaxation time (${\tau }_c$), drag coefficient ($\gamma$), transverse momentum diffusion coefficient ($B_0$), and spatial diffusion coefficient ($D_s$) of a charm quark inside a deconfined medium. Finally, we compare the obtained results with lattice QCD and with various other theoretical models. Good agreement can be observed between the results obtained from CSPM and lattice QCD.

Using a Poincaré-covariant $\mathrm{quark}+\mathrm{diquark}$ Faddeev equation, we provide structural information on the four lightest $(I,J^P)=(\frac{1}{2},{\frac{3}{2}}^{\mp })$ baryon multiplets. These systems may contain five distinct types of diquarks; but in order to obtain reliable results, it is sufficient to retain only isoscalar-scalar and isovector-axialvector correlations, with the latter being especially important. Viewed with low resolution, the Faddeev equation description of these states bears some resemblance to the associated quark model pictures; namely, they form a set of states related via orbital angular momentum excitation: the negative parity states are primarily $\mathsf{P}$-wave in character, whereas the positive parity states are $\mathsf{D}$ wave. However, a closer look reveals far greater structural complexity than is typical of quark model descriptions, with $\mathsf{P}$, $\mathsf{D}$, $\mathsf{S}$, $\mathsf{F}$ waves and interferences between them all playing a large role in forming observables. Large momentum transfer resonance electroexcitation measurements can be used to test these predictions and may thereby provide insights into the nature of emergent hadron mass.

In this study, we investigate the branching ratios of $B_s^0\to a_0(980)[\to K\overline{K},\pi \eta ]a_0(980)$, $B_s^0\to f_0(980)[\to {\pi }^{+}{\pi }^{-},K^{+}{K}^{-}]f_0(980)$, and $B_s^0\to f_0(500)[\to {\pi }^{+}{\pi }^{-}]f_0(500)$ decays in the pQCD approach, wherein the scalar mesons $a_0(980)$, $f_0(980)$, and $f_0(500)$ are regarded as the lowest-lying $q\overline{q}$ state. In the $SU(3)$ nonet, there exists a mixing between the scalars $f_0(980)$ and $f_0(500)$. Thus, we have considered the mixing effect in our calculations to obtain reliable data, and set the mixing angle $\theta$ as [15°, 82°] and [105°, 171°]. Based on the isospin symmetry, we estimated the branching ratios of the $B_s^0\to f_0(980)[\to {\pi }^0{\pi }^0]f_0(980)$ and $B_s^0\to f_0(500)[\to {\pi }^0{\pi }^0]f_0(500)$ decays. The branching ratios of the $B_s^0\to a_0(980)[\to K\overline{K},\pi \eta ]a_0(980)$ decays are much small, while those of the $B_s^0\to f_0(980)[\to \pi \pi ,K\overline{K}]f_0(980)$ and $B_s^0\to f_0(500)[\to \pi \pi ]f_0(500)$ decays are at the order of ${10}^{-6}–{10}^{-5}$, which can be tested in the LHCb and Belle II experiments, hopefully.

In quantum field theory, a consistent prescription to define and deform integration contours in the complex energy plane is needed to evaluate loop integrals and compute scattering amplitudes. In some nonlocal field theories, including string field theory, interaction vertices contain transcendental functions of momenta that can diverge along certain complex directions, thus making it impossible to use standard techniques, such as Wick rotation, to perform loop integrals. The aim of this paper is to investigate the viability of several contour prescriptions in the presence of nonlocal vertices. We consider three “different” prescriptions and establish their (in)equivalence in local and nonlocal theories. In particular, we prove that all these prescriptions turn out to be equivalent in standard local theories, while this is not the case for nonlocal theories where amplitudes must be defined first in Euclidean space, and then analytically continued to Minkowski. We work at one-loop level and focus on the bubble diagram. In addition to proving general results for a large class of nonlocal theories, we show explicit calculations in a string-inspired nonlocal scalar model.

A stable physical system has an energy spectrum that is bounded from below. For quantum systems, the dangerous states of unboundedly low energies should decouple and become null. We propose the principle of nullness and apply it to the bootstrap study of Hermitian and non-Hermitian anharmonic oscillators.

We present an investigation of the Clauser-Horne-Shimony-Holt (CHSH) inequality within a relativistic quantum field theory model built up with a pair of free massive scalar fields $({\phi }_A,{\phi }_B)$ where, as is customary, the indices $(A,B)$ refer to Alice and Bob, respectively. A set of bounded Hermitian operators is introduced by making use of the Weyl operators. A CHSH-type correlator is constructed and evaluated in the Fock vacuum by means of canonical quantization. Although the observed violation of the CHSH inequality turns out to be rather small as compared to Tsirelson’s bound of quantum mechanics, the model can be employed for the study of Bell’s inequalities in the more physical case of gauge theories such as the Higgs models, for which local Becchi-Rouet-Stora-Tyutin (BRST) invariant operators describing both the massive gauge boson as well as the Higgs particle have been devised. These operators can be naturally exponentiated, leading to BRST invariant type of Weyl operators useful to analyze Bell’s inequalities within an invariant BRST environment.

In this work, we explore how modified gravity theories based on the nonmetricity scalar, known as $f(Q)$ gravity, affect the propagation of gravitational waves from inspiraling of binary systems. We discuss forecast constraints on $f(Q)$ gravity by considering standard siren events in two contexts: (i) simulated sources of gravitational waves as black hole–neutron star binary systems, emitting in the frequency band of the third-generation detector represented by the Einstein Telescope (ET); (ii) three standard siren mock catalogs based on the merger of massive black hole binaries that are expected to be observed in the operating frequency band of the Laser Interferometer Space Antenna (LISA). We find that, within the ET sensitivity, in combination with supernova and cosmic chronometer data, it will be possible to test deviations from general relativity at $<3\%$ accuracy in the redshift range $0<z<5$, while the main free parameter of the theory is globally constrained at 1.6% accuracy within the same range. In light of LISA’s forecasts, combined to supernova and cosmic chronometer data, in the best scenario, we find that the main free parameter of the theory will be constrained at 1.6% accuracy up to high redshifts. Therefore, we conclude that future gravitational wave observations by ET and LISA will provide a unique way to test, with good accuracy, the nature of gravity up to very large cosmic distances.

Gravitational lensing in the weak field limit, quasinormal spectra, and gray-body factors are investigated in the Reissner-Nordström spacetime corrected by bounce parameters. Using the Gauss-Bonnet theorem, we analyze the effects of bounce corrections to the weak gravitational deflection angle and find that the divergence of the deflection angle can be suppressed by a bounce correction in the Reissner-Nordström spacetime. We also notice that the bounce correction plays the same role as the Morse potential in the deflection angle. Moreover, we derive the perturbation equations with spin-dependent effective potentials and discuss the quasinormal spectral stability. We observe that the quasinormal spectra have the same behavior in large bounce parameters for different multiple numbers and they decrease significantly if the bounce parameter is much bigger than the charge. We further study the transmission probability of particles scattered by the effective potentials and reveal that the bounce correction introduced into the Reissner-Nordström spacetime increases the gray-body factors of perturbation fields.

We show that the $H_0$ tension can be alleviated in the framework of Horndeski/generalized Galileon gravity. In particular, since the terms depending on $G_5$ control the friction in the Friedmann equation, we construct specific subclasses in which it depends only on the field’s kinetic energy. Since the latter is small at high redshifts, namely at redshifts which affected the CMB structure, the deviations from $\mathrm{\Lambda }\mathrm{CDM}$ cosmology are negligible, however as time passes it increases and thus at low redshifts the Hubble function acquires increased values in a controlled way. We consider two models; one with quadratic and one with quartic dependence on the field’s kinetic energy. In both cases we show the alleviation of the tension, resulting to $H_0\approx 74\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ for particular parameter choices. Finally, we examine the behavior of scalar metric perturbations, showing that the conditions for absence of ghost and Laplacian instabilities are fulfilled throughout the evolution, and we confront the models with Supernovae type Ia and cosmic chronometer data.

It has been recently shown that magnetic reconnection can provide us a novel mechanism to extract black hole rotational energy from Kerr black holes. In this paper, we study the energy extraction from the Kerr–de Sitter black hole via this magnetic reconnection process. The result shows that, with the increase of the cosmological constant, a slowly spinning Kerr–de Sitter black hole can implement the energy extraction better than its Kerr counterpart. Interestingly, although the numerical results show that the maximum values of the power and efficiency slightly decrease with the cosmological constant, the Kerr–de Sitter black hole still has significant advantages when the black hole spin is larger than 1 and the dominant reconnection $X$ point is far away from the event horizon. This is mainly attributed to the higher upper spin bound and wider ergosphere in the presence of the cosmological constant. These results uncover the significant effects of the cosmological constant on the energy extraction via the magnetic reconnection process.

We compute the variation of the Fokker-Wheeler-Feynman total linear and angular momentum of a gravitationally interacting binary system under the second post-Minkowskian retarded dynamics. The resulting $O(G^2)$ equations-of-motion-based, total change in the system’s angular momentum is found to agree with existing computations that assumed balance with angular momentum fluxes in the radiation zone.

We describe general features of formation and disappearance of regular spherically symmetric black holes in semiclassical gravity. The allowed models are critically dependent on the requirement that the resulting objects evolve in finite time according to a distant observer. Violation of the null energy condition is mandatory for this to happen, and we study the properties of the necessary energy-momentum tensor in the vicinity of the apparent horizon. In studies of the kinematics of massive test particles, it is found that the escape from a black hole is possible only on the ingoing trajectories when the particles are overtaken by the contracting outer apparent horizon. Tidal forces experienced by geodesic observers, infalling or escaping, are shown to be finite at the apparent horizon, although this is not true for nongeodesic trajectories.

In recent years there has been an increased interest in neural networks, particularly with regard to their ability to approximate partial differential equations. In this regard, research has begun on so-called physics-informed neural networks (PINNs) which incorporate into their loss function the boundary conditions of the functions they are attempting to approximate. In this paper, we investigate the viability of obtaining the quasinormal modes (QNMs) of nonrotating black holes in four-dimensional space-time using PINNs, and we find that it is achievable using a standard approach that is capable of solving eigenvalue problems (dubbed the eigenvalue solver here). In comparison to the QNMs obtained via more established methods (namely, the continued fraction method and the sixth-order Wentzel, Kramer, Brillouin method) the PINN computations share the same degree of accuracy as these counterparts. In other words, our PINN approximations had percentage deviations as low as $(\delta {\omega }_{\mathrm{Re}},\delta {\omega }_{\mathrm{Im}})=(<0.01\%,<0.01\%)$. In terms of the time taken to compute QNMs to this accuracy, however, the PINN approach falls short, leading to our conclusion that the method is currently not to be recommended when considering overall performance.

Extreme-mass-ratio inspirals will be prized sources for the upcoming space-based gravitational-wave observatory Laser Interferometer Space Antenna (LISA). The hunt for these is beset by many open theoretical and computational problems in both source modeling and data analysis. We draw attention here to one of the most poorly understood: the phenomenon of nonlocal correlations in the space of extreme-mass-ratio-inspiral signals. Such correlations are ubiquitous in the continuum of possible signals (degeneracy) and severely hinder the search for actual signals in LISA data. However, they are unlikely to manifest in a realistic set of putative signals (confusion). We develop an inventory of new analysis tools in order to conduct an extensive qualitative study of degeneracy—its nature, causes, and implications. Previously proposed search strategies for extreme-mass-ratio inspirals are reviewed in the light of our results, and additional guidelines are suggested for the scientific analysis of such sources.

We consider ${\mathcal{R}}^2$ inflation in Palatini gravity, in the presence of scalar fields coupled to gravity. These theories, in the Einstein frame, and for one scalar field $h$, share common features with $K$-inflation models. We apply this formalism for the study of single-field inflationary models, whose potentials are monomials, $V\sim h^n$, with $n$ a positive even integer. We also study the Higgs model nonminimally coupled to gravity. With ${\mathcal{R}}^2$ terms coupled to gravity as $\sim \alpha {\mathcal{R}}^2$, with $\alpha$ constant, the instantaneous reheating temperature $T_{ins}$, is bounded by $T_{ins}\le 0.290m_{\text{Planck}}/{\alpha }^{1/4}$, with the upper bound being saturated for large $\alpha$. For such large $\alpha$ need go beyond slow roll to calculate reliably the cosmological parameters, among these the end of inflation through which $T_{ins}$ is determined. In fact, as the inflaton rolls towards the end of the inflation point, the quartic in the velocity terms, unavoidable in Palatini gravity, play a significant role and cannot be ignored. The values of $\alpha$, and other parameters, are constrained by cosmological data, setting bounds on the inflationary scale $M_s\sim 1/\sqrt{\alpha }$ and the reheating temperature of the Universe.

We develop a method for implementing a proposal on utilizing knowledge of neutron star (NS) equation of state (EoS) for inferring the Hubble constant from a population of binary neutron star (BNS) mergers. This method is useful in exploiting BNSs as standard sirens when their redshifts are not available. Gravitational wave (GW) signals from compact object binaries provide a direct measurement of their luminosity distances, but not their redshifts. Unlike in the past, here we employ a realistic EoS parametrization in a Bayesian framework to simultaneously measure the Hubble constant and refine the constraints on the EoS parameters. The uncertainty in the redshift depends on the uncertainties in the EoS and the mass parameters estimated from GW data. Combining the inferred BNS redshifts with the corresponding luminosity distances, one constructs a redshift-distance relation and deduces the Hubble constant from it. Here, we show that in the Cosmic Explorer era, one can measure the Hubble constant to a precision of $\lesssim 5\%$ (with a 90% credible interval) with a realistic distribution of a thousand BNSs, while allowing for uncertainties in their EoS parameters. Such a measurement can potentially resolve the current tension in the measurements of the Hubble constant from the early- and late-time universe. The methodology implemented in this work demonstrates a comprehensive prescription for inferring the NS EoS and the Hubble constant by simultaneously combining GW observations from merging NSs, while employing a simple population model for NS masses and keeping the merger rate of NSs constant in redshift. This method can be immediately extended to incorporate merger rate, population properties, and additional cosmological parameters.

We study the Brownian motion of a field where there are boundaries in the inflationary field space. Both the field and the boundary undergo Brownian motions with the amplitudes of the noises determined by the Hubble expansion rate of the corresponding de Sitter spacetime. This setup mimics models of inflation in which curvature perturbation is induced from inhomogeneities generated at the surface of the end of inflation. The cases of the drift-dominated regime as well as the diffusion-dominated regime are studied in detail. We calculate the first hitting probabilities as well as the mean number of $e$-folds for the field to hit either of the boundaries in the field space. The implications for models of inflation are reviewed.