$CP$ violation in baryon decay processes is still undiscovered to date. We present a general analysis of the decay-angular distributions and the corresponding $CP$ asymmetries in cascade decays of the type $\mathbb{H}\to R(\to ab)c$, where $\mathbb{H}$ is a heavy hadron that decays through weak interactions $\mathbb{H}\to Rc$ and the resonance $R$ decays strongly via $R\to ab$. Based on the analysis, we propose to search for $CP$ violation in the decay-angular distributions in the cascade decay processes $\mathbb{B}\to \mathcal{B}M$, with $\mathcal{B}$ or $M$ subsequently decaying through strong interactions, where $\mathbb{B}$ is the mother baryon, $\mathcal{B}$ and $M$ are the daughter baryon and meson, respectively, and $M$ has to be spin nonzero. We also present some typical decay channels in which the search for such kinds of $CP$ asymmetries can be performed.

The Ishibashi-Kawai-Kitazawa-Tsuchiya (IKKT) model is a promising candidate for a nonperturbative description of type IIB superstring theory. It is known from analytic approaches and numerical simulations that the IKKT matrix model with a mass term admits interesting cosmological solutions. However, this mass term is often introduced by hand and serves as a regulator in the theory. In the present paper, we show that an effective mass matrix can arise naturally in the IKKT model by imposing a toroidal compactification where the space-time fermions acquire antiperiodic boundary conditions. When six spatial dimensions are chosen to be compact, the effective mass matrix breaks the SO(1,9) space-time symmetry of the IKKT model to $\mathrm{SO}(1,3)\times \mathrm{SO}(6)$. This paves the way for space-time solutions of the IKKT model where SO(1,9) symmetry is naturally broken to $\mathrm{SO}(1,3)\times \mathrm{SO}(6)$.

As the out-of-time-order correlator (OTOC) is a measure of quantum chaos and an important observable in the context of AdS/CFT, we investigate the OTOC of a holographic Skyrmion which is described by an analytical quantum mechanical system from the D4/D8 model (as the holographic QCD). By employing the OTOC defined in quantum mechanics, we derive the formulas and demonstrate the numerical calculations of the OTOC explicitly which is also available for the general case with a central force field. Our numerical evaluation illustrates the behaviors of the OTOC with large $N_c$; however, the expected exponential growth of OTOC is not obtained. Besides, we also take a look at the classical limit of the OTOC and analyze the associated behaviors. At the end of this work, we additionally study the OTOC with three-dimensional Coulomb potential, as another example for the central force field, to support our analyses of the general properties of quantum OTOC.

The collapse of a spherically symmetric ball of dust has been intensively studied in loop quantum gravity (LQG). From a quantum theory, it is possible to recover a semiclassical regime through a polymerization procedure. In this setting, general solutions to the polymerized Einstein field equations (PEFE) will be discussed both for the homogeneous interior and the exterior of the dust cloud. Exterior solutions are particularly interesting since they may lead to a semiclassical version of the Birkhoff’s theorem. It is seen that if time independence of the vacuum is imposed, there exists a class of solutions depending on two parameters. Nevertheless, the possibility of more intricate time-dependent solutions is not ruled out completely. A second approach to study semiclassical spacetimes is by considering an Oppenheimer-Snyder model. Namely, one glues the portion of spacetime containing homogeneous dust with the vacuum part by matching the extrinsic curvatures. In this way, one gets a metric tensor for the vacuum, which can be compared to the one obtained previously. Although these two methods are completely independent from each other, the results we obtained are in perfect agreement.

We consider isolated horizons (Killing horizons up to the second order) whose null flow has the structure of a U(1) principal fiber bundle over a compact Riemann surface. We impose the vacuum Einstein equations (with the cosmological constant) and the condition that the spacetime Weyl tensor is of Petrov D type on the geometry of the horizons. We derive all the solutions in the case when the genus of the surface is $>1$. By doing so for all the nontrivial bundles, we complete the classification. We construct the embedding spacetimes and show that they are locally isometric to the toroidal or hyperbolic generalization of the Taub-NUT-(anti-) de Sitter spacetimes for horizons of genus 1 or $>1$ respectively, after performing Misner’s identification of the spacetime. The horizon bundle structure can be naturally extended to bundle structure defined on the entire spacetime.

We propose a new formula for the entropy of a dynamical black hole—valid to leading order for perturbations off of a stationary black hole background—in an arbitrary classical diffeomorphism covariant Lagrangian theory of gravity in $n$ dimensions. In stationary eras, this formula agrees with the usual Noether charge formula, but in nonstationary eras, we obtain a nontrivial correction term. In particular, in general relativity, our formula for the entropy of a dynamical black hole differs from the standard Bekenstein-Hawking formula $A/4$ by a term involving the integral of the expansion of the null generators of the horizon. We show that, to leading perturbative order, our dynamical entropy in general relativity is equal to $1/4$ of the area of the apparent horizon. Our formula for entropy in a general theory of gravity is obtained from the requirement that a “local physical process version” of the first law of black hole thermodynamics hold for perturbations of a stationary black hole. It follows immediately that for first order perturbations sourced by external matter that satisfies the null energy condition, our entropy obeys the second law of black hole thermodynamics. For vacuum perturbations, the leading-order change in entropy occurs at second order in perturbation theory, and the second law is obeyed at leading order if and only if the modified canonical energy flux is positive (as is the case in general relativity but presumably would not hold in more general theories of gravity). Our formula for the entropy of a dynamical black hole differs from a formula proposed independently by Dong and by Wall. We obtain the general relationship between their formula and ours. We then consider the generalized second law in semiclassical gravity for first order perturbations of a stationary black hole. We show that the validity of the quantum null energy condition (QNEC) on a Killing horizon is equivalent to the generalized second law using our notion of black hole entropy but using a modified notion of von Neumann entropy for matter. On the other hand, the generalized second law for the Dong-Wall entropy is equivalent to an integrated version of QNEC, using the unmodified von Neumann entropy for the entropy of matter.

It is generally believed that tidal deformations of a black hole in an external field, as measured using its gravitational field multipoles, vanish. However, this does not mean that the black hole horizon is not deformed. Here we shall discuss the deformations of a black hole horizon in the presence of an external field using a characteristic initial value formulation. Unlike existing methods, the starting point here is the black hole horizon itself. The effect of, say, a binary companion responsible for the tidal deformation is encoded in the geometry of the spacetime in the vicinity of the horizon. The near horizon spacetime geometry, i.e., the metric, spin coefficients, and curvature components, are all obtained by integrating the Einstein field equations outwards starting from the horizon. This method yields a reformulation of black hole perturbation theory in a neighborhood of the horizon. By specializing the horizon geometry to be a perturbation of Kerr, this method can be used to calculate the metric for a tidally deformed Kerr black hole with arbitrary spin. As a first application, we apply this formulation here to a slowly spinning black hole and explicitly construct the spacetime metric in a neighborhood of the horizon. We propose natural definitions of the electric and magnetic surficial Love numbers based on the Weyl tensor component ${\mathrm{\Psi }}_2$. From our solution, we calculate the tidal perturbations of the black hole, and we extract both the field Love numbers and the surficial Love numbers which quantify the deformations of the horizon.

We study the relationship between the standard or extended thermodynamic phase structure of various anti–de Sitter black holes and the Lyapunov exponents associated with the null and timelike geodesics. We consider dyonic, Bardeen, Gauss-Bonnet, and Lorentz-symmetry breaking massive gravity black holes and calculate the Lyapunov exponents of massless and massive particles in unstable circular geodesics close to the black hole. We find that the thermal profile of the Lyapunov exponents exhibits distinct behavior in the small and large black hole phases and can encompass certain aspects of the van der Waals type small/large black hole phase transition. We further analyze the properties of Lyapunov exponents as an order parameter and find that its critical exponent is $1/2$, near the critical point for all black holes considered here.

Stellar evolution predicts the existence of a mass gap for black hole remnants produced by pair-instability supernova dynamics, whose lower and upper edges are very uncertain. We study the possibility of constraining the location of the upper end of the pair-instability mass gap, which is believed to appear around $m_{\min }\sim 130M_{\odot }$, using gravitational wave observations of compact binary mergers with next-generation ground-based detectors. While high metallicity may not allow for the formation of first-generation black holes on the “far side” beyond the gap, metal-poor environments containing population III stars could lead to such heavy black hole mergers. We show that, even in the presence of contamination from other merger channels, next-generation detectors will measure the location of the upper end of the mass gap with a relative precision close to $\mathrm{\Delta }{m}_{\min }/m_{\min }\simeq 4\%(N_{\det }/100{)}^{-1/2}$ at 90% CL, where $N_{\det }$ is the number of detected mergers with both members beyond the gap. These future observations could reduce current uncertainties in nuclear and astrophysical processes controlling the location of the gap.

It is shown that the values of the ratios $\mathcal{B}(D^0\to a_0(980{)}^{+}{\pi }^{-})/\mathcal{B}(D^0\to a_0(980{)}^{-}{\pi }^{+})$ and $\mathcal{B}(D^{+}\to a_0(980{)}^{+}{\pi }^0)/\mathcal{B}(D^{+}\to a_0(980{)}^0{\pi }^{+})$, recently measured by the BESIII Collaboration, are naturally explained in the four-quark model of the $a_0(980)$ resonance.

We analyze the mass and width of the doubly heavy tetraquark $T_{ccs}$ composed of a heavy diquark and a light-quark cloud with strangeness with assuming that a color antitriplet heavy diquark is a dominant component of the doubly charmed tetraquarks $T_{cc}$ and $T_{ccs}$. We construct an effective Lagrangian for masses of heavy hadrons based on the superflavor symmetry between the doubly heavy tetraquarks and the singly heavy baryons by including the terms that simultaneously break the heavy-quark and light-flavor symmetries, and predict the mass of $T_{ccs}$ as $M(T_{ccs})=4047\pm 11\mathrm{MeV}$. The comparison of this prediction with future experimental observation will give a clue to understand the color structure of the heavy diquark. We also predict the mass of ${\mathrm{\Omega }}_{cc}$ as $M({\mathrm{\Omega }}_{cc})=3706_{-15}^{+14}\mathrm{MeV}$. We next calculate the decay width of $T_{ccs}$, based solely on the light-flavor symmetry, as $\mathrm{\Gamma }(T_{ccs})=42\pm 24\mathrm{MeV}$.

We study how the recent experimental results constrain the gauge sectors of $U(1)$ extensions of the standard model using a novel representation of the parameter space. We determine the bounds on the mixing angle between the massive gauge bosons or, equivalently, the new gauge coupling as a function of the mass $M_{Z^{\prime }}$ of the new neutral gauge boson $Z^{\prime }$ in the approximate range $({10}^{-2},{10}^4)\mathrm{GeV}/c^2$. We consider the most stringent bounds obtained from direct searches for the $Z^{\prime }$. We also exhibit the allowed parameter space by comparing the predicted and measured values of the $\rho$ parameter and those of the mass of the $W$ boson. Finally, we discuss the prospects of $Z^{\prime }$ searches at future colliders.

A search for charged-lepton-flavor violating $\mu \tau qt$ ($q=u$, $c$) interactions is presented, considering both top-quark production and decay. The data analyzed correspond to $140{\mathrm{fb}}^{-1}$ of proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$ recorded with the ATLAS detector at the Large Hadron Collider. The analysis targets events containing two muons with the same electric charge, a hadronically decaying $\tau$-lepton and at least one jet, with exactly one $b$-tagged jet, produced by a $\mu \tau qt$ interaction. Agreement with the Standard Model expectation within 1.6 standard deviations is observed, and limits are set at the 95% confidence level (CL) on the charged-lepton-flavor violation branching ratio of $\mathcal{B}(t\to \mu \tau q)<8.7\times {10}^{-7}$. An effective field theory interpretation is performed yielding 95% CL limits on Wilson coefficients, dependent on the flavor of the associated light quark and the Lorentz structure of the coupling. These range from $|c_{\mathsf{lequ}}^{3(2313)}|/{\mathrm{\Lambda }}^2<0.10{\mathrm{TeV}}^{-2}$ for $\mu \tau ut$ to $|c_{\mathsf{lequ}}^{1(2323)}|/{\mathrm{\Lambda }}^2<1.8{\mathrm{TeV}}^{-2}$ for $\mu \tau ct$. An additional interpretation is performed for scalar leptoquark production inducing charged-lepton-flavor violation, with fixed intergenerational couplings. Upper limits on leptoquark coupling strengths are set at the 95% CL, ranging from ${\lambda }^{\mathrm{LQ}}=1.3$ to ${\lambda }^{\mathrm{LQ}}=3.7$ for leptoquark masses between 0.5 and 2.0 TeV.

Monte Carlo algorithms are barely considered in spin foam quantum gravity. Due to the quantum nature of spin foam amplitudes one cannot readily apply them and the present sign problem is a threat to convergence, and thus efficiency. Yet, ultimately the severity of the sign problem in spin foams is not known. In this article we propose a new probability distribution for coherent (boundary) intertwiners, which we use to define a Markov chain Monte Carlo algorithm. We apply this algorithm to the SU(2) coherent vertex amplitude for various Regge-type boundary data and find convergent, accurate results at far lower costs than the explicit calculation. The resources are instead used to increase the size of boundary spins, bridging the gap to the asymptotic formulas. While the sign problem is not solved, it is under control in the vast majority of cases. We close by discussing how this algorithm can be extended to larger triangulations with boundary and 4d Lorentzian spin foam models. More speculatively, we discuss how this algorithm can be used to sample (Regge-geometric) bulk intertwiners.

The phase space of Bianchi I universes in vacuum Brans-Dicke gravity is analyzed in terms of physical variables. The behavior of the solutions of the field equations near the fixed points (which are solutions of Einstein gravity) is compared with basic ideas of the recent first-order thermodynamics of scalar-tensor gravity, elucidating new phenomenology.

We investigate inflationary particle production associated with a spectator ultralight scalar field, which has recently been proposed as a plausible dark matter candidate. In this framework, we select the Starobinsky potential to drive the inflationary epoch, also discussing the case of a nonminimally coupled inflaton field fueled by a quartic symmetry-breaking potential. We focus on particle production arising from spacetime perturbations, which are induced by inflaton fluctuations during the quasi–de Sitter stage of inflation. In particular, we construct the first-order Lagrangian describing interaction between inhomogeneities and the spectator field, quantifying superhorizon particle production during slow-roll. We then compare this mechanism with gravitational particle production associated with an instantaneous transition from inflation to the radiation dominated era. We show that the number of particles obtained from perturbations is typically non-negligible, and it is significantly enhanced on super-Hubble scales by the nonadiabatic inflationary expansion. Possible implications for primordial entanglement generation are also debated.

Cosmic string networks are the best motivated relics of cosmological phase transitions, being unavoidable in many physically plausible extensions of the Standard Model. Most studies, including those providing constraints from and forecasts of their observational signals, rely on assumptions of featureless networks, neglecting the additional degrees of freedom on the string worldsheet, e.g., charges and currents, which are all but unavoidable in physically realistic models. An extension of the canonical velocity-dependent one-scale model, accounting for all such possible degrees of freedom, has been recently developed. Here we improve its physical interpretation by studying and classifying its possible asymptotic scaling solutions, and in particular how they are affected by the expansion of the Universe and the available energy loss or transfer mechanisms. We find three classes of solutions. For sufficiently fast expansion rates the charges and currents decay and one asymptotes to the Nambu-Goto case, while for slower expansion rates they can dominate the network dynamics. In between the two there is a third regime in which the network, including its charge and current, reaches full scaling. Under specific but plausible assumptions, this intermediate regime corresponds to the matter-dominated era. Our results agree with, and significantly extend, those of previous studies.

The rates of the $X(3872)\to {\pi }^0{\pi }^0{\chi }_{c1}$ and $X(3872)\to {\pi }^{+}{\pi }^{-}{\chi }_{c1}$ decays are estimated in the model of the triangle loop diagrams with charmed $D^{*}\overline{D}D$ and ${\overline{D}}^{*}D\overline{D}$ mesons in the loops. There are the triangle logarithmic singularities in the physical region of the $X(3872)\to {\pi }^0{\pi }^0{\chi }_{c1}$ decay which manifest themselves as narrow peaks in the ${\pi }^0{\chi }_{c1}$ mass spectrum near the $D^0{\overline{D}}^0$ threshold. The model predicts approximately the same branching fractions of the $X(3872)\to {\pi }^0{\pi }^0{\chi }_{c1}$ and $X(3872)\to {\pi }^{+}{\pi }^{-}{\chi }_{c1}$ decays at the level of about $(0.8–1.7)\times {10}^{-4}$. A distinct prediction of the model is the value of the ratio $\mathcal{R}=\mathcal{B}(X(3872)\to {\pi }^{+}{\pi }^{-}{\chi }_{c1})/\mathcal{B}(X(3872)\to {\pi }^0{\pi }^0{\chi }_{c1})\approx 1.1$. It weakly depends on the $X(3872)$ resonance parameters and indicates a significant violation of the isotopic symmetry according to which one would expect $\mathcal{R}=2$.

We investigate how recent updates to neutrino oscillation parameters and the sum of neutrino masses influence the sensitivity of neutrinoless double-beta ($0\nu \beta \beta$) decay experiments. Incorporating the latest cosmological constraints on the sum of neutrino masses and laboratory measurements on oscillations, we determine the sum of neutrino masses for both the normal hierarchy (NH) and the inverted hierarchy (IH). Our analysis reveals a narrow range for the sum of neutrino masses, approximately $0.06\mathrm{eV}/{\mathrm{c}}^2$ for NH and $0.102\mathrm{eV}/{\mathrm{c}}^2$ for IH. Utilizing these constraints, we calculate the effective Majorana masses for both NH and IH scenarios, establishing the corresponding allowed regions. Importantly, we find that the minimum neutrino mass is nonzero, as constrained by the current oscillation parameters. Additionally, we estimate the half-life of $0\nu \beta \beta$ decay using these effective Majorana masses for both NH and IH. Our results suggest that upcoming ton-scale experiments will comprehensively explore the IH scenario, while 100-ton-scale experiments will effectively probe the parameter space for the NH scenario, provided the background index can achieve 1 event/kton-year in the region of interest.