We investigate the behavior of the dense and cold (normalized) quantum chromodynamics (QCD) trace anomaly, $\mathrm{\Delta }$, in the interior of twin neutron stars (obtained from several sets of equations of state in agreement with modern compact-star and multimessenger data) satisfying static and dynamic stability conditions. We scan the formed twin-star parameter space in order to look for effects caused by the presence of a strong first-order phase transition connecting hadron and quark phases by means of a Maxwell construction. We found robustly that $\mathrm{\Delta }$ suffers an abrupt decrease around the transition point, even reaching large negative values ($\mathrm{\Delta }\simeq -0.35$), in marked contrast to current studies pointing out a smooth behavior with $\mathrm{\Delta }\gtrsim 0$ at all densities. Besides, we characterize the behavior of the recently defined conformal factor, $d_c$, in the four categories of twin stars for which we perform comparisons with theoretical constraints put, e.g., by Bayesian studies sometimes adjusted to agree with perturbative QCD at high densities. These analyses allow us to hypothesize modifications in the strong QCD coupling in dense nuclear matter with a strong thermodynamic discontinuity.

We examine how plasma excitations affect the heavy-quark diffusion coefficient in $2+1$-dimensional and glasmalike plasmas, akin to the preequilibrium matter describing relativistic heavy-ion collisions at early times. We find that the transport coefficient $2\kappa$ transverse to and ${\kappa }_z$ along the beam direction display a qualitatively different evolution. We attribute this to the underlying excitation spectra of these systems, thus providing evidence for the existence of nonperturbative properties in the spectrum. This is accomplished by first reconstructing the diffusion coefficients using gauge-fixed correlation functions, which accurately reproduces the time evolution of $2\kappa$ and ${\kappa }_z$. We then modify these excitation spectra to study the impact of their nonperturbative features on the transport coefficients. In particular, we find evidence for a novel transport peak in the low-frequency spectrum that is crucial for heavy-quark diffusion. We also demonstrate that gluonic excitations are broad while scalar excitations associated with ${\kappa }_z$ are narrow and strongly enhanced at low momenta. Our findings indicate that the large values and dynamical properties of transport coefficients in the glasma could originate from genuinely nonperturbative features in the spectrum.

We scrutinize the potential of upcoming ultranear reactor neutrino experiments to detect radiative corrections in the elastic neutrino-electron scattering channel, focusing on the JUNO-TAO and CLOUD detectors, which employ advanced scintillator detection technologies. Previous reactor experiments have already constrained the electron neutrino charge radius, which is a neutrino property associated with a certain subset of the total radiative corrections, and have achieved limits that are only about an order of magnitude away from the Standard Model prediction. Our study demonstrates that JUNO-TAO and CLOUD could discover the neutrino charge radius in the near future, considering the established treatment of the charge radius. However, we show that it is necessary to go beyond this standard treatment. By including the complete set of one-loop level radiative corrections, we find a partial cancellation with the charge radius effect, reducing the experimental sensitivity to this quantity. Nevertheless, JUNO-TAO and CLOUD still have the potential to achieve a $5\sigma$ discovery but over longer timescales within a reasonable operational time frame.

This paper explores the renormalization of scale-free quadratic gravity coupled to the bumblebee field and its potential for dynamically breaking Lorentz symmetry. We conduct one-loop renormalization of the model and calculate the associated renormalization group functions. Furthermore, we compute the one-loop effective potential for the bumblebee field, demonstrating that it acquires a nontrivial vacuum expectation value (VEV) through radiative corrections—a phenomenon known as the Coleman-Weinberg mechanism. This spontaneous breaking of scale invariance, driven by the nonzero VEV of the bumblebee field, leads to Lorentz symmetry violation. As a result, the nonminimal coupling between the bumblebee and gravitational fields induces a spontaneous generation of an Einstein-Hilbert term via radiative corrections, suggesting a possible link between the Planck scale and Lorentz violation phenomena.

Thomas-Whitehead (TW) gravity is a gauge theory of gravitation based on projective geometry. The theory maintains projective symmetry through the TW connection, an affine connection over the volume bundle of the spacetime manifold. TW gravity obtains dynamics through Lovelock expansions in the action while preserving general relativity as a weak field limit. In this paper we clarify the process of lifting tensor and spinor fields from spacetime to the volume bundle and demonstrate that a choice of lifting amounts to a gauge fixing condition. This leads to a natural extension of previous work, where we now realize these prior constructions have been restricted to a particular gauge. In pursuit of generality, we also introduce torsion to the TW connection, leading to new dynamics. In particular, the appearance of torsion induces interaction terms involving gravitational coupling with Yang-Mills fields and Dirac spinors. An explicit realization of this is a geometrically sourced chiral mass term arising from the torsion dynamics.

We explore the post-Newtonian dynamics of spinning black hole (BH) binaries in Einstein-scalar-Gauss-Bonnet (ESGB) gravity, a theory that modifies general relativity by introducing a massless scalar field coupled nonminimally to gravity via the Gauss-Bonnet term. By employing an effective field theory (EFT) approach, we extend the Routhian formalism to incorporate spin effects in scalar interactions. In this formalism, we derive for the first time the effective two-body potential for spinning BHs up to the third post-Newtonian (3PN) order in generic ESGB gravity theories. This potential is expressed in terms of the sensitivities of the BHs, which are then obtained through a matching procedure using analytic BH solutions derived here within a slow-rotation approximation, accurate to seventh order in the Gauss-Bonnet coupling and fifth order in the BH spin. We also examine the thermodynamic properties of these rotating solutions, which, as shown in previous work, yield important insights into the inspiral phase evolution in ESGB gravity.

In the vicinity of spacelike singularities, general relativity predicts that the metric behaves, at each point, as a Kasner space which undergoes a series of “Kasner epochs” and “eras” characterized by certain transition rules. The period during which this process takes place defines a “Kasner eon,” which comes to an end when higher-curvature or quantum effects become relevant. When higher-curvature densities are included in the action, spacetime can undergo transitions into additional Kasner eons. During each eon, the metric behaves locally as a Kasner solution to the higher-curvature density controlling the dynamics. In this paper we identify the presence of Kasner eons in the interior of static and spherically symmetric Lovelock gravity black holes. We determine the conditions under which eons occur and study the Kasner metrics which characterize them, as well as the transitions between them. We show that the null energy condition implies a monotonicity property for the effective Kasner exponent at the end of the Einsteinian eon. We also characterize the Kasner solutions of more general higher-curvature theories of gravity. In particular, we observe that the Einstein gravity condition that the sum of the Kasner exponents adds up to 1, ${\sum }_{i=1}^{D-1}{p}_i=1$, admits a universal generalization in the form of a family of Kasner metrics satisfying ${\sum }_{i=1}^{D-1}{p}_i=2n-1$ which exists for any order-$n$ higher-curvature density and in general dimensions.

Renormalization group correction to general relativity (RGGR) proposes a logarithmic running of the gravitational coupling ($G$), resulting in a modified description of gravity. Analogous to the proposal of dark matter (DM), RGGR has the potential to explain the observed kinematics of the galaxies, including the missing mass problem. We, for the first time, based on the galaxy morphological types, investigate the dynamics of a diverse collection of galaxies present in the Spitzer Photometry for Accurate Rotation Curve (SPARC) catalog. We phenomenologically constrain the RGGR model parameter $(\overline{\nu })$ along with the mass-to-light ratio for a sample of 93 SPARC galaxies, selected from four different morphological types, viz. early, spiral, late, and starburst. Our statistical analysis finds RGGR to fit the observed galaxy kinematics consistently. Additionally, we observe that for the galaxies where RGGR and Navarro–Frenk–White (NFW) profile fare equally well. RGGR demonstrates a competitive performance compared to the DM model. The constrained RGGR model parameter also supports the claim that it has a near-linear dependence on the galactic baryonic mass. From our morphology study, we find that the parameter $\overline{\nu }$ decreases from the early-type to the starburst galaxies. Finally, the renormalization group improved gravity is tested against the two established empirical relations for the SPARC catalog, viz., the Radial Acceleration Relation and the Baryonic Tully Fisher relation, and both are found to satisfy consistently. Importantly, these results are found to be nearly independent of the choice of the Bayesian priors on the model parameters.

In this work, we study cosmological spacetime configurations in $f(Q)$ gravity with nonvanishing symmetric teleparallel connections. It is known that the spatially flat, homogeneous, and isotropic connections can be classified into three sets. Focusing on two of those, we explore the stability of cosmological background evolution near the general relativity regime across radiation, matter, dark energy, and geometric dark energy dominated eras. Our results show that for the standard connection set 1 the general relativity regime can be realized in two ways and both exhibit stable behavior throughout all evolutionary epochs. Conversely, for the alternative connection set 2 the trivial general relativity limit is stable, while the nontrivial option exhibits stability during the radiation era and marginal stability during the matter era, but for the dark energy and geometric dark energy eras our results are inconclusive. Furthermore, we discuss the general conditions on the function $f(Q)$ that physically viable models should obey, and point out that for a generic $f(Q)$ the alternative connection sets 2 and 3 are prone to trigger a sudden singularity. This can happen even near the otherwise good looking general relativity regime, as we demonstrate by an explicit numerical example. Hence the alternative configurations could be problematic already on the background level.

Mathematicians have been proposing for some time that the Monge-Ampère equation, a nonlinear generalization of the Poisson equation, where a trace of the Hessian is replaced by its determinant, provides an alternative nonrelativistic description of gravity. The Monge-Ampère equation is an affine invariant, has rich geometric properties, connects to optimal transport theory, and remains bounded at short distances. Monge-Ampère gravity, which uses a slightly different form of the Monge-Ampère equation, naturally emerges through the application of large-deviation principle to a Brownian system of indistinguishable and independent particles. In this work we provide a physical formulation of this mathematical model, study its theoretical viability and confront it with observations. We show that Monge-Ampère gravity cannot replace the Newtonian gravity as it does not withstand the solar-system test. We then show that Monge-Ampère gravity can describe a scalar field, often evoked in modified theories of gravity such as Galileons. We show that Monge-Ampère gravity, as a nonlinear model of a new scalar field, is screened at short distances, and behaves differently from Newtonian gravity above galactic scales but approaches it asymptotically. Finally, we write a relativistic Lagrangian for Monge-Ampère gravity in flat spacetime, which is the field equation of a sum of the Lagrangians of all Galileons. We also show how the Monge-Ampère equation can be obtained from the fully covariant Lagrangian of quartic Galileon in the static limit. The connection between optimal transport theory and modified theories of gravity with second-order field equations, unravelled here, remains a promising domain to further explore.

Gravitational lensing offers unique opportunities to learn about the astrophysical origin of distant sources, the abundance of intervening objects acting as lenses, and gravity and cosmology in general. However, all this information can only be retrieved as long as one can disentangle each effect from the finite number of observables. In the geometric optics regime, typical of electromagnetic radiation, when the wavelength of the lensed signal is small compared to the size of the lens, there are invariance transformations that change the mass of the lens and the source-lens configuration but leave the observables unchanged. Neglecting this “mass-sheet degeneracy” can lead to biased lens parameters or unrealistic low uncertainties, which could then transfer to an incorrect cosmography study. This might be different for gravitational waves as their long wavelengths can be comparable to the lens size and lensing enters into the wave-optics limit. We explore the existence of invariance transformations in the wave-optics regime of gravitational-wave lensing, extending previous work and examining the implications for astrophysical and cosmological studies. We study these invariance transformations using three different methods of increasing level of complexity: template mismatch, Fisher Matrix, and Bayesian parameter estimation. We find that, for a sufficiently loud signal, the degeneracy is partially broken and the lens and cosmological parameters, e.g. $H_0$, can be retrieved independently and unbiased. In current ground-based detectors, though, considering also population studies, a strong constraint on these parameters seems quite remote and the prevailing degeneracy implies a larger uncertainty in the lens model reconstruction. However, with better sensitivity of the third-generation ground-based detectors, a meaningful constraint on $H_0$ is possible to obtain.

The Reggeized pion is expected to provide the main contribution to the forward cross section in light meson photoproduction reactions with charge exchange at high energies. We discuss the Reggeization of pion exchange in charged pion photoproduction with an emphasis on consistency with current conservation. We show that the gauge-invariant amplitude for the exchange of a particle with a generic even spin $J\ge 2$ in the $t$ channel is analytic at $J=0$ and that it can be interpreted in terms of the nucleon electric current. This enables us to reconcile the dynamics in the $s$ and $u$ channel, which involves also nucleon exchanges, with the amplitude expressed in terms of $t$-channel partial waves, as required by Regge theory.

We perform a detailed study of neutrino-electron elastic scattering using the monoenergetic ${}^7\mathrm{Be}$ neutrinos in Borexino, with an emphasis on exploring the differences between the contributions of ${\nu }_e$, ${\nu }_{\mu }$, and ${\nu }_{\tau }$. We find that current data are capable of measuring these components such that the contributions from ${\nu }_{\mu }$ and ${\nu }_{\tau }$ cannot be zero, although distinguishing between them is challenging—the differences stemming from Standard Model radiative corrections are insufficient without significantly more precise measurements. In studying these components, we compare predicted neutrino-electron scattering event rates within the Standard Model (accounting for neutrino oscillations), as well as going beyond the Standard Model in two ways. We allow for nonunitary evolution to modify neutrino oscillations, and find that with a larger exposure ($\sim 30\mathrm{x}$), Borexino may provide relevant information for constraining nonunitarity, and that JUNO may be able to accomplish this with its data collection of ${}^7\mathrm{Be}$ neutrinos. We also consider novel ${\nu }_{\mu }$- and ${\nu }_{\tau }$-electron scattering from a gauged $U(1{)}_{L_{\mu }-L_{\tau }}$ model, showing consistency with previous analyses of Borexino and this scenario, but also demonstrating the impact of uncertainties on Standard Model mixing parameters on these results.

Measurements of the strong-phase difference between $D^0$ and ${\overline{D}}^0\to {\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$ are performed in bins of phase space. The study exploits a sample of quantum-correlated $D\overline{D}$ mesons collected by the BESIII experiment in $e^{+}{e}^{-}$ collisions at a center-of-mass energy of 3.773 GeV, corresponding to an integrated luminosity of $2.93{\mathrm{fb}}^{-1}$. Here, $D$ denotes a neutral charm meson in a superposition of flavor eigenstates. The reported results are valuable for measurements of the $CP$-violating phase $\gamma$ (also denoted ${\varphi }_3$) in $B^{\pm }\to D{K}^{\pm }$, $D\to {\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$ decays, and the binning schemes are designed to provide good statistical sensitivity to this parameter. The expected uncertainty on $\gamma$ arising from the precision of the strong-phase measurements, when applied to very large samples of $B$-meson decays, is around 1.5° or 2°, depending on the binning scheme. The binned strong-phase parameters are combined to give a value of $F_{+}^{4\pi }=0.746\pm 0.010\pm 0.004$ for the $CP$-even fraction of $D^0\to {\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$ decays, which is around 30% more precise than the previous best measurement of this quantity.

The search for low-mass dark matter (DM), which has gained much interest recently, goes in parallel with the identification of new detection channels and the development of suitable detectors. The detection of the resulting small energy depositions is challenging, requiring extremely high sensitivity only achievable by cryogenic thermal detectors, which might be put to the limit. Thus, understanding the processes that can limit the performance of these detectors can be crucial for evaluating the feasibility of the proposed new detection schemes and, eventually, designing the detectors and tuning their performance. In this paper, we focus on a promising detection scheme, the excitation of single optical phonons in polar materials, to evaluate one of the possible and less understood limiting factors of cryogenic thermal detectors, i.e., the phonon dynamics in the target/absorber. We present a detailed theoretical analysis, within an entirely ab initio scheme, of the downconversion and propagation processes undergone by optical phonons, created by the interaction of a low-mass DM particle in an ${\text{Al}}_2{\mathrm{O}}_3$ target, until they reach the interface with a phonon Al collector. After a preliminary methodological survey that reveals the limitations of any relaxation time approximation (RTA)-based method, we develop a beyond-RTA phonon Monte Carlo for three-dimensional materials that allows us to introduce the spatial dimension of the device and address questions about the impact of target size and scattering position. We also analyze the effect of the phonon energy and wave vector, and show that isotopes can, perhaps counterintuitively, result in a larger heat flux by providing transport channels of higher velocities, thus favoring detection. Our results suggest that, though challenging, the direct detection of light DM via athermal phonon generation appears feasible, and phonon downconversion followed by quasiballistic propagation does not appear to be a major bottleneck in terms of reducing the signal.

We consider the running coupling constant in holographic models supported by Einstein-dilaton-Maxwell action for heavy and light quarks. To obtain the dependence of the running coupling constant $\alpha$ on temperature and chemical potential we impose boundary conditions on the dilaton field that depend on the position of the horizon. We use two types of boundary conditions: a simple boundary condition with the dilaton field vanishing at the horizon and a boundary condition that ensures an agreement with lattice calculations of string tension between quarks at zero chemical potential. The location of the first order phase transitions in the $(\mu ,T)$ plane does not depend on the dilaton boundary conditions for light and heavy quarks. At these phase transitions, the function $\alpha$ undergoes jumps depending on temperature and chemical potential. We also show that for the second boundary conditions the running coupling decreases with a temperature increase, and the dependence on temperature and chemical potential both for light and heavy quarks is actually specified in quark-gluon plasma (QGP) phase by functions of one variable, demonstrating in this sense automodel behavior.

In this study, we explore the thermodynamics of heavy quarkonium within the context of a spinning black hole background. Specifically, we analyze the impact of angular momentum on various thermodynamic properties of heavy quarkonium, including interquark distance, free energy, binding energy, entropy, entropic force, and internal energy, based on the thermodynamic relationships. Our results demonstrate that angular momentum diminishes the maximum interquark distance, thereby facilitating quarkonium dissociation. Furthermore, we note that angular momentum suppresses free energy. The analysis of binding energy reveals that angular momentum enhances the dissociation of mesons into free quarks and antiquarks. Additionally, our findings indicate that angular momentum augments entropy and entropic force, thereby accelerating quarkonium dissociation. Angular momentum also increases internal energy at extended interquark distances. Lastly, we observe that the effects of angular momentum on quarkonium are more significant when the axis of the quark pair $Q\overline{Q}$ is perpendicular to the direction of angular momentum.

We introduce the concept of an emergent electric field. This is distinguished from the fundamental one in that the emergent electric field directly appears in observations through the Lorentz force, while the latter enters the phase space as the canonical momentum of the electromagnetic field. In Hamiltonian classical electromagnetism this concept naturally appears after introducing the topological $\theta$ term. Furthermore, we show that in the spherically symmetric model the concept of an emergent electric field allows us to formulate a modified theory of electromagnetism that is otherwise impossible. The relation between the fundamental and the emergent electric fields is derived from the imposition of general covariance of the electromagnetic strength tensor, which is a nontrivial task in the canonical formulation the modified theory is based on. We couple this theory to emergent modified gravity, where a similar distinction between spacetime and gravity is made such that the spacetime, which defines the observable geometry, is an emergent field composed of the fundamental gravitational field. In this more encompassing emergent field theory coupling gravity and electromagnetism, we show that the spherically symmetric model contains a nonsingular black hole solution where not only modified gravity but also modified electromagnetism is crucial for a robust singularity resolution which, as a consequence, excludes the existence of (super)extremal black holes.

Astrophysical compact objects are usually studied using a perfect fluid model. However, in astrophysical processes out of equilibrium, dissipative effects become important to describe the dynamics of the system. In this work we obtain gauge-invariant nonspherical perturbations of a self-gravitating nonperfect fluid in spherical spacetime. We use the Gerlach-Sengupta formalism to work with gauge-invariant metric perturbations and the Gundlach-Martín-García approach to transform the equations of tensor perturbations into scalar equations. We calculate the dynamics of the dissipative contributions, e.g., viscosity and heat flux, using the Müller-Israel-Stewart equations in the gauge-invariant formalism. We obtain a set of field equations for the evolution of matter and metric perturbations in the polar and axial sectors. Specifically, in the former we find two wave equations sourced by the anisotropic contributions, and the evolution of all matter perturbations for radiative modes ($l\ge 2$). In the axial sector, we find one wave equation coupled to the evolution of matter perturbations. Finally, we comment on the contribution of dissipative effects in the lower-order multipoles ($l=0,1$) for both sectors.

Gravitational waves exhibit the unique signature of their spin-2 nature in processes of wave scattering, due to the interaction between spin and a background spacetime. Since the spin effect is more pronounced for longer wavelengths and gravitational waves sourced by binaries have a long wavelength, it may become an important effect in addition to the wave effect. We study the propagation of gravitational waves lensed by a Kerr black hole by numerically solving the Teukolsky equation with a source term of the equal-mass circular binary, taking into account both spin effect and wave effect. We find helicity-dependent small-period oscillation in the power spectrum of the amplification factor in the forward direction and the oscillation is enhanced as spin of a prograde Kerr black hole increases.