As shown by Marunovic and Murkovic [Classical Quantum Gravity 31, 045010 (2014)], nonminimal d-stars, composite structures consisting of a boson star and a global monopole nonminimally coupled to the general relativistic field, can have extremely high gravitational compactness. In a previous paper we demonstrated that these ground-state stationary solutions are sometimes additionally characterized by shells of bosonic matter located far from the center of symmetry [Phys. Rev. D 93, 044022 (2016)]. In order to investigate the question of stability posed by Marunovic and Murkovic, we investigate the stability of several families of d-stars using both numerical simulations and linear perturbation theory. For all families investigated, we find that the most highly compact solutions, along with those solutions exhibiting shells of bosonic matter, are unstable to radial perturbations and are therefore poor candidates for astrophysically relevant black hole mimickers or other highly compact stable objects.

We construct a theory of gravity in which a propagating massive vector field arises from a quadratic curvature invariant. The Einstein-Cartan formulation and a partial suppression of torsion ensure the absence of ghost and strong-coupling problems, as we prove with nonlinear Lagrangian and Hamiltonian analysis. Augmenting general relativity with a propagating torsion vector, our theory provides a purely gravitational origin of Einstein-Proca models and constrains their parameter space. As an outlook to phenomenology, we discuss the gravitational production of fermionic dark matter.

We apply a method (“eLCQ”) to find the asymptotic spectrum of a Hamiltonian from its symmetries to two-dimensional adjoint QCD. Streamlining the approach, we construct a complete set of asymptotic eigenfunctions in all parton sectors and use it in a basis-function approach to find the spectrum of the full theory. We are able to reproduce previous results including the degeneracy of fermionic and bosonic masses at the supersymmetric point, and to understand the properties of the lowest states in the massless theory. The approach taken here is continuous at fixed parton number, and therefore complementary to standard formulations, e.g. discretized light-cone quantization (DLCQ). Despite its limitation to rather small parton numbers, it can be used to test and validate conclusions of other frameworks in an independent way.

Rare decays mediated by $b\to s\nu \overline{\nu }$ transitions have been reported by the Belle II experiment. The branching ratio of the decay $B^{+}\to K^{+}\nu \overline{\nu }$ is found to be enhanced with respect to the standard model value. If taken at face value, the implications are profound; either lepton flavor universality is violated at the (multi)-TeV-scale, or light new physics is involved. This holds in general if $\mathcal{B}(B^{+}\to K^{+}\nu \overline{\nu })$ exceeds $1.2\times {10}^{-5}(1.3\times {10}^{-5})$ at $1\sigma$ ($2\sigma$), which tightens with a decreasing upper limit on $\mathcal{B}(B\to K^{*}\nu \overline{\nu })$, that is in reach of the Belle II experiment. In view of the strong constraints on electron-muon universality violation in $|\mathrm{\Delta }b|=|\mathrm{\Delta }s|=1$ processes, viable explanations are heavy, (5–10)-TeV tree-level new physics mediators that couple only to tau-flavors, or lepton flavor violating ones. In addition, couplings of similar size to both left- and right-handed quarks are generically required, implying nonminimal beyond the standard model sectors which are carefully balanced against flavor constraints. The decay $B_s^0\to \text{invisibles}$ can shed light on whether new physics is light or heavy. In the former case, branching ratios can be as large as ${10}^{-5}$.

We give a general derivation of Ginsparg-Wilson relations for both Dirac and Majorana fermions in any dimension. These relations encode continuous and discrete chiral, parity and time-reversal anomalies and will apply to the various classes of free-fermion topological insulators and superconductors (in the framework of a relativistic quantum field theory in Euclidean spacetime). We show how to formulate the exact symmetries of the lattice action and the relevant index theorems for the anomalies.

The Born cross sections and effective form factors of the process $e^{+}{e}^{-}\to \mathrm{\Lambda }{\overline{\mathrm{\Sigma }}}^0+\mathrm{c}.\mathrm{c}.$ are measured at 14 center-of-mass energy points from 2.3094 to 3.0800 GeV, based on data corresponding to an integrated luminosity of $(478.5\pm 4.8){\mathrm{pb}}^{-1}$ collected with the BESIII detector. A nonzero Born cross section is observed at the center-of-mass energy of 2.3094 GeV with a statistical significance of more than five standard deviations, and the cross sections at other energies are obtained with improved precision compared to earlier measurements from the BABAR Collaboration. The Born cross-section line shape is described better by a shape considering the strong-interaction effects than by a pQCD motivated functional form.

We report measurements of the branching fractions and direct $CP$ asymmetries of the decays $B^0\to K^{+}{\pi }^{-}$, $B^{+}\to K^{+}{\pi }^0$, $B^{+}\to K^0{\pi }^{+}$, and $B^0\to K^0{\pi }^0$, and use these for testing the standard model through an isospin-based sum rule. In addition, we measure the branching fraction and direct $CP$ asymmetry of the decay $B^{+}\to {\pi }^{+}{\pi }^0$ and the branching fraction of the decay $B^0\to {\pi }^{+}{\pi }^{-}$. The data are collected with the belle II detector from $e^{+}{e}^{-}$ collisions at the $\mathrm{\Upsilon }(4S)$ resonance produced by the SuperKEKB asymmetric-energy collider and contain $387\times {10}^6$ bottom-antibottom meson pairs. Signal yields are determined in two-dimensional fits to background-discriminating variables, and range from 500 to 3900 decays, depending on the channel. We obtain $-0.03\pm 0.13\pm 0.04$ for the sum rule in agreement with the standard model expectation of zero and with a precision comparable to the best existing determinations.

We revisit the connection between Hawking radiation and high-frequency dispersions for a Schwarzschild black hole following the work of [R. Brout, S. Massar, R. Parentani and P. Spindel, Phys. Rev. D 52, 4559 (1995)]. After confirming the robustness of Hawking radiation for monotonic dispersion relations, we consider nonmonotonic dispersion relations that deviate from the standard relation only in the trans-Planckian domain. Contrary to the common belief that Hawking radiation is insensitive to UV physics, it turns out that Hawking radiation is subject to significant modifications after the scrambling time. Depending on the UV physics at the singularity, the amplitude of Hawking radiation could diminish after the scrambling time, while the Hawking temperature remains the same. Our finding is thus not contradictory to earlier works regarding the robustness of the Hawking temperature.

A new form of quasiclassical space-time dynamics for constrained systems reveals how quantum effects can be derived systematically from canonical quantization of gravitational systems. These quasiclassical methods lead to additional fields, representing quantum fluctuations and higher moments, that are coupled to the classical metric components. The new fields describe nonadiabatic quantum dynamics and can be interpreted as implicit formulations of nonlocal quantum corrections in a field theory. This field-theory aspect is studied here for the first time, applied to a gravitational system for which a tractable model is constructed. Static solutions for the relevant fields can be obtained in almost closed form. They reveal new properties of potential near-horizon and asymptotic effects in canonical quantum gravity and demonstrate the overall consistency of the formalism.

It is shown that the evolution of an axially and reflection symmetric fluid distribution, satisfying the Tolman condition for thermal equilibrium, is not accompanied by the emission of gravitational radiation. This result, which was conjectured by Bondi many years ago, expresses the irreversibility associated to the emission of gravitational waves. The observational consequences emerging from this result are commented. The resulting models are not only nondissipative and vorticity free, but also shear-free and geodesic, furthermore all their complexity factors vanish.

In this paper we study the gravitational lensing effect for the Schwarzschild solution with holonomy corrections. We use two types of approximation methods to calculate the deflection angle, namely the weak and strong field limits. For the first method, we calculate the deflection angle up to the fifth order of approximation and show the influence of the parameter $\lambda$ (in terms of loop quantum gravity) on it. In addition, we construct expressions for the magnification, the position of the lensed images and the time delay as functions of the coefficients from the deflection angle expansion. We find that $\lambda$ increases the deflection angle. In the strong field limit, we use a logarithmic approximation to compute the deflection angle. We then write four observables, in terms of the coefficients $b_1$, $b_2$, and $u_m$, namely: the asymptotic position approached by a set of images ${\theta }_{\infty }$, the distance between the first image and the others $s$, the ratio between the flux of the first image and the flux of all other images $r_m$, and the time delay between two photons $\mathrm{\Delta }{T}_{2,1}$. We then use the experimental data of the black hole Sagittarius $A^{\star }$ and calculate the observables and the coefficients of the logarithmic expansion. We find that the parameter $\lambda$ increases the deflection angle, the separation between the lensed images and the delay time between them. In contrast, it decreases the brightness of the first image compared to the others.

A cosmological model based on holographic scenarios is formulated in a flat Friedmann-Robertson-Walker universe. To formulate this model, the cosmological horizon is assumed to have a general entropy and a general temperature (including Bekenstein-Hawking entropy and Gibbons-Hawking temperature, respectively). In addition, a holographiclike connection [N. Komatsu, Eur. Phys. J. C 83, 690 (2023)] and Padmanabhan’s holographic equipartition law are assumed for the entropy and temperature, and the Friedmann and acceleration equations are derived from these. The derived Friedmann and acceleration equations include both the entropy and the temperature and are slightly complicated, but can be combined into a single simple equation, corresponding to a similar equation that describes the background evolution of the universe in time-varying $\mathrm{\Lambda }(t)$ cosmologies. The simple equation depends on the entropy but not on the temperature because the temperatures in the Friedmann and acceleration equations cancel each other. These results imply that the holographiclike connection should be consistent with Padmanabhan’s holographic equipartition law through the present model and that the entropy plays a more important role. When the Gibbons-Hawking temperature is used as the temperature, the Friedmann and acceleration equations are found to be equivalent to those for a $\mathrm{\Lambda }(t)$ model. A particular case of the present model is also examined, applying a power-law corrected entropy.

We study the Hartle-Hawking no-boundary proposal in the framework of Hořava-Lifshitz gravity. The former is a prominent hypothesis that describes the quantum creation of the universe, while the latter is a potential theory of quantum gravity that ensures renormalizability and unitarity, at least in the so-called projectable version. For simplicity, we focus on a global universe composed of a set of local universes each of which is closed, homogeneous, and isotropic. Although applying the no-boundary proposal to Hořava-Lifshitz gravity is not straightforward, we demonstrate that the proposal can be formulated within the Hořava-Lifshitz gravity utilizing the Lorentzian path integral formulation of quantum gravity. In projectable Hořava-Lifshitz gravity, the no-boundary wave function of the global universe inevitably contains entanglement between different local universes induced by “dark matter as integration constant.” On the other hand, in the nonprojectable version, the no-boundary wave function of the global universe is simply the direct product of wave functions of each local universe. We then discuss how the no-boundary wave function is formulated under Dirichlet and Robin boundary conditions. For the Dirichlet boundary condition, we point out that its on-shell action diverges due to higher-dimensional operators, but this problem can in principle be ameliorated by taking into account the renormalization group flow. However, utilizing the Picard-Lefschetz theory to identify the relevant critical points and performing the complex lapse integration, we find that only the tunneling wave function can be obtained, as in the case of general relativity. On the other hand, for the Robin boundary condition with a particular imaginary Hubble expansion rate at the initial hypersurface, the no-boundary wave function can be achieved in the Hořava-Lifshitz gravity.

Electromagnetic field confinement due to plasma near accreting black holes can trigger superradiant instabilities at the linear level, limiting the spin of black holes and providing novel astrophysical sources of electromagnetic bursts. However, nonlinear effects might jeopardize the efficiency of the confinement, rending superradiance ineffective. Motivated by understanding nonlinear interactions in this scenario, here we study the full $3+1$ nonlinear dynamics of Maxwell equations in the presence of plasma by focusing on regimes that are seldom explored in standard plasma-physics applications, namely a generic electromagnetic wave of very large amplitude but small frequency propagating in an inhomogeneous, overdense plasma. We show that the plasma transparency effect predicted in certain specific scenarios is not the only possible outcome in the nonlinear regime: plasma blowout due to nonlinear momentum transfer is generically present and allows for significant energy leakage of electromagnetic fields above a certain threshold. We argue that such effect is sufficient to dramatically quench the plasma-driven superradiant instability around black holes even in the most optimistic scenarios.

We investigate the degree to which current ultrahigh-energy cosmic ray observations above the ankle support a common maximum rigidity for all nuclei, often called a Peters cycle, over alternative scenarios for the cosmic ray spectra escaping sources. We show that a Peters cycle is not generally supported by the data when compared with these alternatives for the scenarios studied. We explore the observational signatures of non-Peters cycle scenarios, and the opportunities to explore both ultrahigh-energy cosmic ray source conditions, as well as physics beyond the Standard Model they present.

We introduce a systematic and quantitative methodology for establishing the presence of neutrino oscillatory signals due to the hadron-quark phase transition (PT) in failing core-collapse supernovae from the observed neutrino event rate in water- or ice-based neutrino detectors. The methodology uses a likelihood ratio in the frequency domain as a test-statistic; it is employed for quantitative analysis of neutrino signals without assuming the frequency, amplitude, starting time, and duration of the PT-induced oscillations present in the neutrino events and thus it is suitable for analyzing neutrino signals from a wide variety of numerical simulations. We test the validity of this method by using a core-collapse simulation of a 17 solar-mass star by Zha et al. [Astrophys. J. 911, 74 (2021) ]. Based on this model, we further report the presence of a PT-induced oscillations quantitatively for a core-collapse supernovae out to a distance of $\sim 10\mathrm{kpc}$, $\sim 5\mathrm{kpc}$ for IceCube and to a distance of $\sim 10\mathrm{kpc}$, $\sim 5\mathrm{kpc}$, and $\sim 1\mathrm{kpc}$ for a 0.4 Mt mass water Cherenkov detector. This methodology will aid the investigation of a future galactic supernova and the study of hadron-quark phase in the core of core-collapse supernovae.

We study the effects of the first nontrivial hexaquark, $d^{*}(2380)$, on the equation of state of dense neutron star matter and investigate the consequences of its existence for neutron stars. The matter in the core regions of neutron stars is described using density-dependent relativistic mean-field theory. Our results show that within the parameter spaces examined in our paper, (i) the critical density at which the $d^{*}$ condensate emerges lies between 4 and 5 times the nuclear saturation density, (ii) $d^{*}$ hexaquarks are found to exist only in rather massive neutron stars, (iii) only relatively small fractions of the matter in the core of a massive neutron star may contain hexaquarks.

We consider macroscopic motion of quantum field systems. The Zubarev statistical operator allows us to describe several types of motion of such systems in thermal equilibrium. We formulate the corresponding effective theory on the language of a functional integral. The effective Lagrangian is calculated explicitly for the fermionic systems interacting with dynamical gauge fields. Possible applications to physics of quark-gluon plasma are discussed.

Axion-gluon interaction induces quadratic couplings between the axion and the matter fields. We find that, if the axion is an ultralight dark matter field, it induces small oscillations of the mass of the hadrons as well as other nuclear quantities. As a result, atomic energy levels oscillate. We use currently available atomic spectroscopy data to constrain such axion-gluon coupling. We also project the sensitivities of future experiments, such as ones using molecular and nuclear clock transitions. We show that current and near-future experiments constrain a finely tuned parameter space of axion models. These can compete with or dominate the already-existing constraints from oscillating neutron electric dipole moment and supernova bound, in addition to those expected from near future magnetometer-based experiments. We also briefly discuss the reach of accelerometers and interferometers.