In this paper, we discuss relativistic hydrodynamics for a massless Dirac fermion in ($2+1$) dimensions, which has the parity anomaly—a global ’t Hooft anomaly between $\mathrm{U}(1)$ and parity symmetries. We investigate how hydrodynamics implements the party anomaly, particularly focusing on the transport phenomena at the boundary. Based on the parity anomaly matching and the second law of local thermodynamics, we find $\mathrm{U}(1)$ and entropy currents localized at the boundary, as well as the bulk anomalous current with vanishing divergence. These edge currents are similar to the ($1+1$)-dimensional chiral transports, but the coefficients are given by half of theirs. We also generalize our discussion to more general anomalies among multiple $\mathrm{U}(1)$ symmetries and single ${\mathbb{Z}}_2$ symmetry.

Heat always flows from hotter to a colder temperature until thermal equilibrium is finally restored in agreement with the usual (zeroth, first, and second) laws of thermodynamics. However, Tolman and Ehrenfest demonstrated that the relation between inertia and weight uniting all forms of energy in the framework of general relativity implies that the standard equilibrium condition is violated in order to maintain the validity of the first and second law of thermodynamics. Here we demonstrate that the thermal equilibrium condition for a static self-gravitating fluid, besides being violated, is also heavily dependent on the underlying spacetime geometry (whether Riemannian or non-Riemannian). As a particular example, a new equilibrium condition is deduced for a large class of Weyl and $f(R)$ type gravity theories. Such results suggest that experiments based on the foundations of the heat theory (thermal sector) may also be used for confronting gravity theories and prospect the intrinsic geometric nature of the spacetime structure.

We investigate the separability of the Klein-Gordon equation on near horizon of $d$-dimensional rotating Myers-Perry black hole in two limits: (i) generic extremal case and (ii) extremal vanishing horizon case. In the first case, there is a relation between the mass and rotation parameters so that black hole temperature vanishes. In the latter case, one of the rotation parameters is restricted to zero on top of the extremality condition. We show that the Klein-Gordon equation is separable in both cases. Also, we solved the radial part of that equation and discuss its behavior in small- and large-$r$ regions.

Primordial black holes (PBHs) have entered the forefront of theoretical cosmology, due their potential role in phenomena ranging from gravitational waves, to dark matter, to galaxy formation. While producing PBHs from inflationary fluctuations naively would seem to require a large deceleration of the inflaton from its velocity at the horizon exit of CMB scales, in this work we demonstrate that an acceleration from a relatively small downward step in the potential that is transited in much less than an e-fold amplifies fluctuations as well. Depending on the location of the step, such PBHs could explain dark matter or the black holes detected by the gravitational wave interferometers. The perturbation enhancement has a natural interpretation as particle production due to the nonadiabatic transition associated with the step, which then leads to amplification in the associated curvature perturbations by the redshifting of the excess kinetic energy after the step, as in an ultra-slow-roll phase.

We present our results on the electromagnetic form factor of pion over a wide range of $Q^2$ using lattice QCD simulations with Wilson-clover valence quarks and highly improved staggered quark sea quarks. We study the form factor at the physical point with a lattice spacing $a=0.076\mathrm{fm}$. To study the lattice spacing and quark mass effects, we also present results for 300 MeV pion at two different lattice spacings $a=0.04$ and 0.06 fm. The lattice calculations at the physical quark mass appear to agree with the experimental results. Through fits to the form factor, we estimate the charge radius of pion for physical pion mass to be $⟨r_{\pi }^2⟩=0.42(2){\mathrm{fm}}^2$.

We have studied analytically the longitudinally boost-invariant motion of a relativistic dissipative fluid with spin. We have derived the analytic solutions of spin density and spin chemical potential as a function of proper time $\tau$ in the presence of the viscous tensor and the second order relaxation time corrections for spin. Interestingly, analogous to the ordinary particle number density and chemical potential, we find that the spin density and spin chemical potential decay as $\sim {\tau }^{-1}$ and $\sim {\tau }^{-1/3}$, respectively. These solutions can serve both to gain insight on the dynamics of spin polarization in relativistic heavy-ion collisions and as test beds for further numerical codes.

The isospin breaking effect plays an essential role in generating hadronic molecular states with a very tiny binding energy. Very recently, the LHCb Collaboration observed a very narrow doubly charmed tetraquark $T_{cc}^{+}$ in the $D^0{D}^0\pi$ mass spectrum, which lies just below the $D^0{D}^{*+}$ threshold around 273 keV. In this work, we study the $D^0{D}^{*+}/D^{+}{D}^{*0}$ interactions with the one-boson-exchange effective potentials and consider the isospin breaking effect carefully. We not only reproduce the mass of the newly observed $T_{cc}^{+}$ very well in the doubly charmed molecular tetraquark scenario, but also predict the other doubly charmed partner resonance $T_{cc}^{\prime +}$ with $m=3876\mathrm{MeV}$, and $\mathrm{\Gamma }=412\mathrm{keV}$. The prime decay modes of the $T_{cc}^{\prime +}$ are $D^0{D}^{+}\gamma$ and $D^{+}{D}^0{\pi }^0$. The peculiar characteristic mass spectrum of the $D^0{D}^{*+}/D^{+}{D}^{*0}$ molecular systems can be applied to identify the doubly charmed molecular states.

Based on $3.19{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data accumulated at the center-of-mass energy 4.178 GeV with the BESIII detector operating at the BEPCII collider, the electromagnetic Dalitz decay $D^{*0}\to D^0{e}^{+}{e}^{-}$ is observed for the first time with a statistical significance of $13.2\sigma$. The ratio of the branching fraction of $D^{*0}\to D^0{e}^{+}{e}^{-}$ to that of $D^{*0}\to D^0\gamma$ is measured to be $(11.08\pm 0.76\pm 0.49)\times {10}^{-3}$. By using the world average value of the branching fraction of $D^{*0}\to D^0\gamma$, the branching fraction of $D^{*0}\to D^0{e}^{+}{e}^{-}$ is determined to be $(3.91\pm 0.27\pm 0.17\pm 0.10)\times {10}^{-3}$, where the first uncertainty is statistical, the second is systematic and the third is from external input of the branching fraction for $D^{*0}\to D^0\gamma$.

We present the measurement of the first to fourth order moments of the four-momentum transfer squared, $q^2$, of inclusive $B\to X_c{\ell }^{+}{\nu }_{\ell }$ decays using the full Belle dataset of $711{\mathrm{fb}}^{-1}$ of integrated luminosity at the $\mathrm{\Upsilon }(4S)$ resonance where $\ell =e$, $\mu$. The determination of these moments and their systematic uncertainties open new pathways to determine the absolute value of the Cabibbo-Kobayashi-Maskawa matrix element $V_{cb}$ using a reduced set of matrix elements of the heavy quark expansion. In order to identify and reconstruct the $X_c$ system, we reconstruct one of the two $B$-mesons using machine learning techniques in fully hadronic decay modes. The moments are measured with progressively increasing threshold selections on $q^2$ starting with a lower value of $3.0{\mathrm{GeV}}^2$ in steps of $0.5{\mathrm{GeV}}^2$ up to a value of $10.0{\mathrm{GeV}}^2$. The measured moments are further unfolded, correcting for reconstruction and selection effects as well as QED final state radiation. We report the moments separately for electron and muon final states and observe no lepton flavor universality violating effects.

In this paper, we establish a fully string-theoretic framework for calculating one-loop Higgs masses directly from first principles in perturbative closed-string theories. Our framework makes no assumptions other than world sheet modular invariance and is therefore applicable to all closed strings, regardless of the specific string construction utilized. This framework can also be employed even when spacetime supersymmetry is broken (and even when this breaking occurs at the Planck scale), and can be utilized for all scalar Higgs fields, regardless of the particular gauge symmetries they break. This therefore includes the Higgs field responsible for electroweak symmetry breaking in the Standard Model. Notably, using our framework, we demonstrate that a gravitational modular anomaly generically relates the Higgs mass to the one-loop cosmological constant, thereby yielding a string-theoretic connection between the two fundamental quantities which are known to suffer from hierarchy problems in the absence of spacetime supersymmetry. We also discuss a number of crucial issues involving the use and interpretation of regulators in UV/IR-mixed theories such as string theory, and the manner in which one can extract an effective field theory (EFT) description from such theories. Finally, we analyze the running of the Higgs mass within such an EFT description, and uncover the existence of a “dual IR” region which emerges at high energies as the consequence of an intriguing scale-inversion duality symmetry. We also identify a generic stringy effective potential for the Higgs fields in such theories. Our results can therefore serve as the launching point for a rigorous investigation of gauge hierarchy problems in string theory.

Recently a generalization of the Fefferman-Graham gauge for asymptotically locally anti–de Sitter spacetimes, called the Weyl-Fefferman-Graham (WFG) gauge, has been proposed. It was shown that the WFG gauge induces a Weyl geometry on the conformal boundary. The Weyl geometry consists of a metric and a Weyl connection. Thus, this is a useful setting for studying dual field theories with background Weyl symmetry. Working in the WFG formalism, we find the generalization of obstruction tensors, which are Weyl-covariant tensors that appear as poles in the Fefferman-Graham expansion of the bulk metric for even boundary dimensions. We see that these Weyl-obstruction tensors can be used as building blocks for the Weyl anomaly of the dual field theory. We then compute the Weyl anomaly for $6d$ and $8d$ field theories in the Weyl-Fefferman-Graham formalism and find that the contribution from the Weyl structure in the bulk appears as cohomologically trivial modifications. Expressed in terms of the Weyl-Schouten tensor and extended Weyl-obstruction tensors, the results of the holographic Weyl anomaly up to $8d$ also reveal hints on its expression in any dimension.

We adapt the dual-null foliation to the functional Schrödinger representation of quantum field theory and study the behavior of quantum probes in plane-wave space-times near the null singularity. A comparison between the Einstein-Rosen and the Brinkmann patch, where the latter extends beyond the first, shows a seeming tension that can be resolved by comparing the configuration spaces. Our analysis concludes that Einstein-Rosen space-times support exclusively configurations with nonempty gravitational memory that are focused to a set of measure zero in the focal plane with respect to a Brinkmann observer. To conclude, we provide a rough framework to estimate the qualitative influence of backreactions on these results.

We present a computationally efficient (time-domain) multipolar waveform model for quasicircular spin-aligned compact binary coalescences. The model combines the advantages of the numerical-relativity informed, effective-one-body (EOB) family of models with a post-adiabatic solution of the equations of motion for the inspiral part of the two-body dynamics. We benchmark this model against other state-of-the-art waveforms in terms of efficiency and accuracy. We find a speed-up of one to two orders of magnitude compared to the underlying time-domain eob model for the total mass range $2–100M_{\odot }$. More specifically, for a low total-mass system, such as a binary neutron star with equal masses of $1.4M_{\odot }$, like GW170817, the computational speedup is around 100 times; for an event with total mass $\sim 40M_{\odot }$ and mass ratio $\sim 3$, like GW190412, the speedup is by a factor of $\sim 20$, while for a binary system of comparable masses and total mass of $\sim 70M_{\odot }$, like GW150914, it is by a factor of $\sim 10$. We demonstrate that the new model is extremely faithful to the underlying eob model with unfaithfulness less than 0.01% across the entire applicable region of parameter space. Finally, we present successful applications of this new waveform model to parameter estimation studies and tests of general relativity.

In [U. H. Danielsson et al., J. High Energy Phys. 10 (2017) 171.] a string theory inspired alternative to gravitational collapse was proposed, consisting of a bubble of AdS space made up of ingredients from string theory. These ultra compact objects are $9/8$ times the size of the corresponding Schwarzschild black hole, but being within the photosphere are almost indistinguishable from them. Slowly rotating counterparts of these black shells were constructed in [U. Danielsson and S. Giri, J. High Energy Phys. 07 (2018) 070.] which closely mimic a Kerr black hole, but have a quadrupole moment that differs from Kerr. Recently, [U. Danielsson et al., Phys. Rev. D 104, 124011 (2021).] studied the dynamical stability of the stationary black shells against radial perturbations and accretion of matter, and examined a two parameter family of fluxes required for stability. In this paper, we reexamine the rotating black shells with particular attention to the constraints imposed by this dynamical analysis for nonrotating shells. Extrapolating these results to rotating shells, we find that they can indeed support themselves at a critical point in the gravitational potential. Additionally, requiring that they settle back to their new Buchdahl radius after accreting matter, uniquely fixes the fluxes required for dynamical stability. The flux parameters turn out to have an extremely simple form, and fulfill one of the constraints for perturbative radial stability while exactly saturating the other. The preferred quadrupole moment that we find, given some physical assumptions, is 7% less than Kerr.

We study the scalar radiation emitted by a source orbiting a Schwarzschild–anti–de Sitter black hole in circular geodesics. We obtain the emitted power using quantum field theory in curved spacetimes at tree level with reflective boundary conditions at infinity. We compare our results with the ones obtained in Schwarzschild and Schwarzschild–de Sitter ($\mathrm{\Lambda }>0$) spacetimes. In the Schwarzschild–de Sitter spacetime we observe an enhancement of the emitted power associated to the lower multipole modes, when compared with the Schwarzschild case. In contrast, for the Schwarzschild–anti–de Sitter spacetime, the enhancement is rather of the higher multipole modes.

The recently proposed Nieh-Yan modified teleparallel gravity is a parity-violating gravity model that modifies the general relativity equivalent teleparallel gravity by a Nieh-Yan term. This model is healthy and simple in form. In this paper, we consider the application of this model to the Solar System and investigate its slow-motion and weak-field approximation in terms of the parametrized post-Newtonian formalism. We find that all of the post-Newtonian parameters of the model are the same as those of general relativity, which makes the model compatible with the Solar System experiments.

The approach of dynamical systems is a useful tool to investigate the cosmological history that follows from modified theories of gravity. It provides qualitative information on the typical background solutions in a parametrized family of models, through the computation of the fixed points and their characters (attractor, repeller, or saddle), allowing, for instance, the knowledge of which regions on the parameter space of the models generate the desired radiation-, matter-, and dark energy–dominated eras. However, the traditional proposal for building dynamical systems for an $f(R)$ theory in the Palatini formalism assumes the invertibility of a function that depends on the specific Lagrangian functional form, which is not true, for example, for the particular theory of exponential gravity ($f(R)=R-\alpha R_{*}(1-e^{-R/R_{*}})$). In this work, we propose an alternative choice of variables to treat $f(R)$ models in their Palatini formulation, which do include exponential gravity. We derive some general results that can be applied to a given model of interest and present a complete description of the phase space for exponential gravity. We show that Palatini exponential gravity theories have a final attractor critical point with an effective equation of state parameter $w_{\mathrm{eff}}=-1$ (for $\alpha >1$), $w_{\mathrm{eff}}=-2/3$ (for $\alpha =1$), and $w_{\mathrm{eff}}=0$ (for $\alpha <1$). Finally, our analytical results are compared with numerical solutions of the field equations.

Gravitational waves emitted by distorted black holes, such as those arising from the coalescence of binary black holes, or a falling compact star into a supermassive black hole, carry not only information about the corresponding spacetime but also the information about the environment surrounding the black holes. In this paper, we study the effects of the dark matter halos with three different density profiles on the gravitational axial perturbations of a Schwarzschild-like black hole. For this purpose, we first consider modified Schwarzschild black holes with three different dark matter profiles and derive the equation of motion of the axial perturbations of the modified Schwarzschild metric. It is shown that by ignoring the dark matter perturbations, a Regge-Wheeler-like master equation with a modified potential for the axial perturbation can be obtained explicitly. Then, we calculate the complex frequencies of the quasinormal modes of the Schwarzschild-like black hole in the dark matter halos by applying the sixth-order WKB method. The corresponding gravitational wave spectra with the effects of the dark matter halos have also been discussed.

Infrared dressing of bosonic or fermionic heavy particles by a cloud of massless particles to which they couple is studied as a possible production mechanism of ultralight dark matter or dark radiation in a radiation-dominated cosmology. We implement an adiabatic expansion valid for wavelengths much smaller than the Hubble radius combined with a nonperturbative and manifestly unitary dynamical resummation method to study the time evolution of an initial single heavy-particle state. We find a striking resemblance to the process of particle decay: the initial amplitude of the single particle decays in time, not exponentially but with a power law with anomalous dimension $\propto t^{-\mathrm{\Delta }/2}$ featuring a crossover to $t^{-\mathrm{\Delta }}$ as the heavy particle becomes nonrelativistic in both bosonic and fermionic cases suggesting certain universality. At long time the asymptotic state is an entangled state of the heavy and massless particles. The entanglement entropy is shown to grow under time evolution describing the flow of information from the initial single particle to the final multiparticle state. The expectation value of the energy momentum tensor in the asymptotic state is described by two independent fluids each obeying covariant conservation, one of heavy particles and the other of relativistic (massless) particles (dark radiation). Both fluids share the same frozen distribution function and entropy as a consequence of entanglement.