We write explicitly the complete Lorentzian metric of a singularity-free spacetime where a black hole transitions into a white hole located in its same asymptotic region. In particular, the metric interpolates between the black and white horizons. The metric satisfies the Einstein field equations up to the tunneling region. The matter giving rise to the black hole is described by the Oppenheimer-Snyder model, corrected with loop-quantum-cosmology techniques in the quantum region. The interior quantum geometry is fixed by a local Killing symmetry, broken at the horizon transition. At large scale, the geometry is determined by two parameters: the mass of the hole and the duration of the transition process. The latter is a global geometrical parameter. We give the full metric outside the star in a single coordinate patch.

We present a detailed analysis of a general relativistic static spherical symmetric distribution in which both the radial and tangential pressures follow a master polytropic equation of state that generalizes the standard treatment and avoids the appearance of singularities in the system. In particular, we find the corresponding Lane-Emden equation and integrate it for a wide range of values of the parameters involved. We explore the parameter space with the aim to find the set of parameters leading to reasonable physical solutions. Also, we considered the effect of spherically symmetric perturbations of the matter variables in order to analyze the possible apparition of cracking within the compact distribution.

We revisit the motion of massless particles with anyonic spin in the horizon of Kerr-Newman geometry. As recently shown, such particles can move within the horizon of the black hole due to the coupling of charges associated with a two-parametric central extension of the two-dimensional Carroll group to the magnetic field generated by the black hole—the so-called “anyonic spin-Hall effect.” We show that the previously computed magnetic field is not invariant under Carroll diffeomorphisms and find another result which respects these symmetries of the horizon. We also consider a more astrophysically relevant case of a (weakly charged) rotating back hole placed in a uniform magnetic field, which could, for instance, be induced by the surrounding plasma. We show that a qualitatively similar magnetic field assisted anyonic spin-Hall effect takes place, even in the absence of black hole rotation. The theoretical possibility of a motion induced by a magnetic monopole is also studied.

We investigate the possibility that the observed behavior of test particles outside galaxies, which is usually explained by assuming the existence of dark matter, is the result of the dynamical evolution of particles in a Weyl type geometry, and its associated conformally invariant Weyl geometric quadratic gravity. As a first step in our investigations we write down the simplest possible conformally invariant gravitational action, constructed in Weyl geometry, and containing the Weyl scalar, and the strength of the Weyl vector only. By introducing an auxiliary scalar field, the theoretical model can be reformulated in the Riemann geometry as scalar-vector-tensor theory, containing a scalar field, and the Weyl vector, respectively. The field equations of the theory are derived in the metric formalism, in the absence of matter. A specific static, spherically symmetric model, in which the Weyl vector has only a radial component, is considered. In this case, an exact analytic solution of the gravitational field equations can be obtained. The behavior of the galactic rotation curves is also considered in detail, and it is shown that an effective geometric mass term, with an associated density profile, can also be introduced. Three particular cases, corresponding to some specific functional forms of the Weyl vector, are also investigated. A comparison of the model with a selected sample of galactic rotation curves is also performed when an explicit breaking of conformal invariance is introduced, which allows the fix of the numerical values of the free parameters of the model. Our results show that Weyl geometric models can be considered as a viable theoretical alternative to the dark matter paradigm.

In this paper, we consider the effects of adding curvature in extended cosmologies involving a free-to-vary neutrino sector and different parametrizations of dark energy (DE). We make use of the Planck 2018 cosmic microwave background temperature and polarization data, baryon acoustic oscillations and Pantheon type Ia supernovae data. Our main result is that a nonflat Universe cannot be discarded in light of the current astronomical data, because we find an indication for a closed Universe in most of the DE cosmologies explored in this work. On the other hand, forcing the Universe to be flat can significantly bias the constraints on the equation of state of the DE component and its dynamical nature.

Primordial black holes (PBHs) can be the source for all or a part of today’s dark matter density. Inflation provides a mechanism for generating the seeds of PBHs in the presence of a temporal period where the velocity of an inflaton field $\varphi$ rapidly decreases toward 0. We compute the primordial power spectra of curvature perturbations generated during Gauss-Bonnet (GB) corrected Higgs inflation in which the inflaton field has not only a nonminimal coupling to gravity but also a GB coupling. For a scalar-GB coupling exhibiting a rapid change during inflation, we show that curvature perturbations are sufficiently enhanced by the appearance of an effective potential $V_{\mathrm{eff}}(\varphi )$ containing the structures of plateau type, bump type, and their intermediate type. We find that there are parameter spaces in which PBHs can constitute all dark matter for these three types of $V_{\mathrm{eff}}(\varphi )$. In particular, models with bump and intermediate types give rise to primordial scalar and tensor power spectra consistent with the recent Planck data on scales relevant to the observations of the cosmic microwave background. This property is attributed to the fact that the number of e-foldings $\mathrm{\Delta }{N}_c$ acquired around the bump region of $V_{\mathrm{eff}}(\varphi )$ can be as small as a few, in contrast to the plateau type, where $\mathrm{\Delta }{N}_c$ typically exceeds the order of 10.

We investigate how charmonium hadroproduction at fixed-target energies can be used to constrain the gluon distribution in pions. Using nonrelativistic QCD (NRQCD) formulation, the $J/\psi$ and $\psi (2S)$ cross sections as a function of longitudinal momentum fraction $x_F$ from pions and protons colliding with light targets, as well as the $\psi (2S)$ to $J/\psi$ cross section ratios, are included in the analysis. The color-octet long-distance matrix elements are found to have a pronounced dependence on the pion parton distribution functions (PDFs). This study shows that the $x_F$ differential cross sections of pion-induced charmonium production impose strong constraints on the pion’s quark and gluon PDFs. In particular, the pion PDFs with larger gluon densities provide a significantly better description of the data. It is also found that the production of the $\psi (2S)$ state is associated with a larger quark-antiquark contribution, compared with $J/\psi$.

We consider a system of two cavities separated by a reflecting boundary of finite mass that is free to move and bounded to its equilibrium position by a harmonic potential. This yields an effective mirror-field interaction, as well as an effective interaction between the field modes mediated by the movable boundary. Two massless scalar fields are defined in each cavity. We consider the second-order interacting ground state of the system, that contains virtual excitations of both mirror’s degrees of freedom and of the scalar fields. We investigate the correlation functions between field observables in the two cavities and find that the squared scalar fields in the two cavities, in the interacting ground state, are anticorrelated. We discuss the dependence of the correlation on the distance of the two points considered from the mirror’s average position and on its mass and oscillation angular frequency. These results show a sort of communication between the two half-spaces separated by the movable mirror, mediated by its position fluctuations. Observability of this new phenomenon exploiting two- or many-body dispersion interactions between polarizable bodies is discussed. The dependence on a cutoff frequency introduced to regularize the frequency integrations, as well as the case of a real conductor, are also discussed.

The $\rho (1450)$ vector meson (${\rho }^{\prime }$) is becoming increasingly important to properly describe precision observables. We analyze a set of decay modes and cross sections, in the low-energy regime, to determine the role played by this meson. This is done through the extraction of the parameters for its description, in the context of the vector meson dominance model and its effective hadronic interactions, involving the low mass lying hadrons ($\rho$, $\omega$, and $\pi$). In a first step, we determine the parameters of the model from ten decay modes which are insensitive to the ${\rho }^{\prime }$. Then, we consider the $\omega \to 3\pi$ decay and exhibit the need to extend the description, by incorporating the ${\rho }^{\prime }$ and a contact term as prescribed by the Wess-Zumino-Witten anomaly. In a second step, we incorporate the data from the $e^{+}{e}^{-}\to 3\pi$ cross section (as measured by SND, CMD2, BABAR, and BESIII) and then the $e^{+}{e}^{-}\to {\pi }^0{\pi }^0\gamma$ data (as measured by SND and CDM2) to further restrict the ${\rho }^{\prime }$ parameters validity region. As an application of the results, we compute the $e^{+}{e}^{-}\to 4\pi$ cross section for the so-called omega channel, measured by BABAR, and find a good description of the data considering the parameters found. As a byproduct, the coupling between $\rho$, $\omega$, and $\pi$ ($g_{\rho \omega \pi }=11.314\pm 0.383{\mathrm{GeV}}^{-1}$) is found to be consistent with all the relevant observables, upon the inclusion of the ${\rho }^{\prime }$ and the contact term.

We derive a general formula for the replica partition function in the vacuum state for a large class of interacting theories with fermions, with or without gauge fields, using the equal-time formulation on the light front. The result is used to analyze the spatial entanglement of interacting Dirac fermions in two-dimensional QCD. Particular attention is paid to the issues of infrared cutoff dependence and gauge invariance. The Renyi entropy for a single interval is given by the rainbow dressed quark propagator to order $\mathcal{O}(N_c)$. The contributions to order $\mathcal{O}(1)$ are shown to follow from the off-diagonal and off mass-shell mesonic T-matrix, with no contribution to the central charge. The construction is then extended to mesonic states on the light front and shown to probe the moments of the partonic PDFs for large light-front separations. In the vacuum and for small and large intervals, the spatial entanglement entropy following from the Renyi entropy is shown to be in agreement with the Ryu-Takayanagi geometrical entropy using a soft-wall ${\mathrm{AdS}}_3$ model of two-dimensional QCD.

We investigate exclusive electroproduction of ${\pi }^{-}{\mathrm{\Delta }}^{++}$ within the handbag approach in which the helicity amplitudes factorize into generalized parton distributions (GPDs) and hard partonic subprocesses. We define the $p-\mathrm{\Delta }$ transversity GPDs while the helicity nonflip GPDs are taken from the literature. For the numerical estimates of observables we utilize large-$N_C$ results in order to relate a few of the $p-\mathrm{\Delta }$ GPDs to the proton-proton ones and neglect all other GPDs. In the calculation of the twist-2 and twist-3 subprocess amplitudes we take into account quark transverse momenta in combination with Sudakov suppressions. The partial cross sections for ${\gamma }^{*}p\to {\pi }^{-}{\mathrm{\Delta }}^{++}$ are predicted in the large-$N_C$ limit.

Within the Standard Model, we investigate the $CP$ violations and the $K_S^0-K_L^0$ asymmetries in $D^{\pm }\to K^{*}(892{)}^0{\pi }^{\pm }+{\overline{K}}^{*}(892{)}^0{\pi }^{\pm }\to K_{S,L}^0{\pi }^0{\pi }^{\pm }$ decays basing on the factorization-assisted topological-amplitude (FAT) approach and the topological amplitude (TA) approach of Cheng and Chiang [Phys. Rev. D 104, 073003 (2021).]. We find that the $CP$ violations in these decays $A_{CP}^{K_{S,L}^0}$ can exceed the order of ${10}^{-3}$ in the two approaches and consist of three parts: the indirect $CP$ violations in $K^0-{\overline{K}}^0$ mixing $A_{CP,K_{S,L}^0}^{\mathrm{mix}}$, the direct $CP$ violations in charm decays $A_{CP,K_{S,L}^0}^{\mathrm{dir}}$, and the new $CP$ violation effects $A_{CP,K_{S,L}^0}^{\mathrm{int}}$, which are induced from the interference between two tree (Cabibbo-favored and doubly Cabibbo-suppressed) amplitudes with the neutral kaon mixing. The indirect $CP$ violations in $K^0-{\overline{K}}^0$ mixing play a dominant role in $A_{CP}^{K_{S,L}^0}$; the new $CP$ violation effects have a non-negligible contribution to $A_{CP}^{K_{S,L}^0}$. We estimate the numerical results of the $K_S^0-K_L^0$ asymmetries $R_{K_S-K_L}^{D^{\pm }}$ and find that there exists a large difference between the numerical results in the FAT approach and that of the TA approach. We present the numbers of $D^{\pm }$ events-times-efficiency needed to observe the $CP$ violations and the $K_S^0-K_L^0$ asymmetries at the level of 3 standard deviations ($3\sigma$). We also find that if one adopts the values of the decay time parameters $t_0=3.0{\tau }_S$ and $t_1=10.0{\tau }_S$, the new $CP$ violation effect $A_{CP,K_S^0}^{\mathrm{int}}$ would dominate the $CP$ violation in $D^{\pm }\to K^{*}(892{)}^0{\pi }^{\pm }+{\overline{K}}^{*}(892{)}^0{\pi }^{\pm }\to K_S^0{\pi }^0{\pi }^{\pm }$ decays and could be observed with $6.7\times {10}^6$ and $6.5\times {10}^6$ $D^{\pm }$ events-times-efficiency in the FAT approach and the TA approach, respectively. Our results could be tested by the LHCb (Large Hadron Collider beauty), Belle II, and BESIII experiments.

We measure the branching fraction for the Cabibbo-suppressed decay $D^0\to K_S^0{K}_S^0{\pi }^{+}{\pi }^{-}$ and search for $CP$ violation via a measurement of the $CP$ asymmetry $A_{CP}$ as well as the $T$-odd triple-product asymmetry $a_{CP}^T$. We use $922{\mathrm{fb}}^{-1}$ of data recorded by the Belle experiment, which ran at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The branching fraction is measured relative to the Cabibbo-favored normalization channel $D^0\to K_S^0{\pi }^{+}{\pi }^{-}$; the result is $\mathcal{B}(D^0\to K_S^0{K}_S^0{\pi }^{+}{\pi }^{-})=[4.79\pm 0.08(\mathrm{stat})\pm 0.10(\mathrm{syst})\pm 0.31(\mathrm{norm})]\times {10}^{-4}$, where the first uncertainty is statistical, the second is systematic, and the third is from uncertainty in the normalization channel. We also measure $A_{CP}=[-2.51\pm 1.44(\mathrm{stat}{)}_{-0.10}^{+0.11}(\mathrm{syst})]\%$, and $a_{CP}^T=[-1.95\pm 1.42(\mathrm{stat}{)}_{-0.12}^{+0.14}(\mathrm{syst})]\%$. These results show no evidence of $CP$ violation.

Two spatial regions $B$ and $R$ are hyperentangled if the generalized entropy satisfies $S_{\mathrm{gen}}^{B\cup R}<S_{\mathrm{gen}}^R$. If in addition all future (or all past) directed inward null shape deformations of $B$ decrease $S_{\mathrm{gen}}^{B\cup R}$, then we show that the causal development of $B$, with $R$ held fixed, must be incomplete. This result eliminates the null energy condition from the assumptions of a recently proven singularity theorem. Instead, we assume a quantum version of the Bousso bound. Taking $R$ to contain the Hawking radiation after the Page time, our theorem predicts a singularity in the past causal development of the black hole interior. This is surprising because the classical spacetime is nonsingular in the past. However, one finds that Cauchy slices that are required to contain $R$ do not remain in the semiclassical regime. The quantum singularities predicted by our theorem are an obstruction to further semiclassical evolution, generalizing the singularities of classical general relativity.

The rate of particle creation in a resonantly oscillating cavity is known to be approximately constant at large evolution times. Employing the Schwinger-Keldysh diagrammatic technique, we show that nonlinear interactions generate nonzero quantum averages and significantly enhance this rate. To illustrate this phenomenon, we consider a massless scalar field with a quartic interaction in a one-dimensional cavity with perfectly reflecting walls oscillating at twice the fundamental frequency.

Metric descriptions of gravitation, among them general relativity as today’s established theory, are founded on assumptions summarized by the Einstein equivalence principle (EEP). Its violation would hint at unknown physics and could be a leverage for the development of quantum gravity. Atomic clocks are excellent systems to probe aspects of EEP connected to (proper) time and have evolved into a working horse for tests of local position invariance (LPI). Even though the operational definition of time requires localized and idealized clocks, quantum systems like atoms allow for spatial superpositions that are inherently delocalized. While quantum experiments have tested other aspects of EEP, no competitive test of LPI has been performed or proposed allowing for an intrinsic delocalization. We extend the concepts for tests of the universality of clock rates (one facet of LPI) to atom interferometry generating delocalized quantum clocks. The proposed test depends on proper time with a favorable scaling and is, in contrast to fountain clocks, robust against initial conditions and recoil effects. It enables optical frequencies so that the projected sensitivity exceeds the one of state-of-the-art localized clocks. These results extend our notion of time, detached from classical and localized philosophies.

A topological approach has been successfully used to study the properties of the light ring and the null circular orbit in a generic black hole background. However, for the equatorial timelike circular orbit, quite different from the light ring case, its radius is closely dependent of the energy and angular momentum of a test particle. This fact seems to restrict the extension of the topological treatment to the timelike circular orbit. In this paper, we confirm that the angular momentum does not affect the asymptotic behavior of the constructed vector with its zero points denoting the equatorial timelike circular orbits. As a result, a well-behaved topology to characterize the equatorial timelike circular orbits can be constructed. Our study shows that the total topological number of the timelike circular orbits vanishes for a generic black hole, which is dependent of the energy of the particle. Significantly, it reveals that if the timelike circular orbits exist, they always come in pairs for fixed angular momentum. Meanwhile, the stable and unstable timelike circular orbits have positive or negative winding number. Of particular interest is that the marginally stable circular orbit corresponds to the bifurcation point of the zero point of the constructed vector. Moreover, we also examine the case when the particle energy acts as the control parameter. It is shown that there will be topological phase transition when the value of the particle energy is one. Below this value, the timelike circular orbits always come in pairs for fixed energy. Otherwise, we will have one more unstable timelike circular orbit. Such a topological phase transition actually measures whether there are bounded orbits. We further apply the treatment to the Kerr black hole. All the results given in a generic black hole background are exactly reproduced. These strongly indicate that our topological approach can be generalized to the equatorial timelike circular orbits.

We investigate resonance crossings of a charged body moving around a Kerr black hole immersed in an external homogeneous magnetic field. This system can serve as an electromagnetic analog of a weakly nonintegrable extreme mass ratio inspiral (EMRI). In particular, the presence of the magnetic field renders the conservative part of the system nonintegrable in the Liouville sense, while the electromagnetic self-force causes the charged body to inspiral. By studying the system without the self-force, we show the existence of an approximate Carter-like constant and discuss how resonances grow as a function of the perturbation parameter. Then, we apply the electromagnetic self-force to investigate crossings of these resonances during an inspiral. Averaging the energy and angular momentum losses during crossings allows us to employ an adiabatic approximation for them. We demonstrate that such adiabatic approximation provides results qualitatively equivalent to the instantaneous self-force evolution, which indicates that the adiabatic approximation may describe the resonance crossing with sufficiently accuracy in EMRIs.

It is often said that there is no gravity theory based on local action principles giving rise to firewall black hole solutions. Additionally, Guo and Mathur [Int. J. Mod. Phys. D 31, 2242009 (2022).] have cast doubt on the observability of firewall echoes due to the closed trapped surface produced by a backreaction of macroscopic in-falling wave packets. In this paper, we bring Einstein-Maxwell-Dilaton action as a toy model that serves as counterexample to these assertions. Actions with Maxwell and dilaton fields emerge from several fundamental theories, such as the low energy limit of (super) string theory or Kaluza-Klein compactifications. In these systems, the black hole solution has two curvature singularities. We will show that the outer singularity inside the event horizon can cause significant change to the outside, close to the extremal limit, making a macroscopic reflective barrier near the event horizon that would lead to “observable” gravitational wave echoes in this toy model. Additionally, we also call into question the argument by Guo et al. [J. High Energy Phys. 07 (2018) 162.] claiming that a very small fraction of the backscattered photons will be able to escape back to infinity from the firewall, using these black holes as a counterexample.