The Belle II experiment and other ongoing and projected lepton facilities are expected to greatly enhance the sensitivity to the electric dipole moment (EDM) and anomalous magnetic moment ($g-2$) for the tau lepton, making it timely to explore models that predict these observables. In this work, we study a class of models in which the tau mass is generated radiatively. As a result, sizable EDM and $g-2$ of the tau lepton arise as a natural consequence of the radiative mass generation mechanism at the electroweak scale. We present two benchmark models with different hypercharge assignments. The first model contains neutral fermions and charged scalars. We find that the model can predict a large signal of the tau EDM, $d_{\tau }=\mathcal{O}({10}^{-19})e\mathrm{cm}$, and $g-2$, $a_{\tau }=\mathcal{O}({10}^{-5})$, which are within the reach of future updates of their measurements. In contrast, the second model, containing a charged fermion and neutral scalars, yields a similar magnitude but different sign for $g-2$, and predicts a comparatively smaller EDM signal. Our models serve as well-motivated benchmarks for new physics scenarios in which radiative tau mass generation leads to sizable tau dipole moments.

We investigate the hard exclusive photoproduction of photon-meson pairs at leading twist and leading order in perturbative QCD and focus on pseudoscalar mesons $\mathrm{M}\in \{{\pi }^{\pm },{\pi }^0,\eta ,{\eta }^{\prime }\}$. Compact analytical expressions are obtained for the amplitudes involving quark generalized parton distributions, with the two-gluon components of the $\eta$ and ${\eta }^{\prime }$ distribution amplitudes included. The numerical analysis is performed in the moderate-$\xi$ region, where valence-quark generalized parton distributions are expected to be important. In this region, we find a strong impact of the pion-pole term in $\gamma {\pi }^{\pm }$ production and a non-negligible effect for neutral mesons. We also observe a marked dependence of $\gamma {\eta }^{\prime }$ photoproduction on two-gluon contributions. This process offers enhanced sensitivity to the shape of the generalized parton distributions already at leading order, while the tested dependence on the meson distribution amplitude and the renormalization scale introduces further theoretical uncertainties, the latter emphasizing the need for next-to-leading-order corrections. Our results provide a concise analytical framework and a numerical baseline for future studies.

We present constraints on low-mass dark matter electron scattering and absorption interactions using a SuperCDMS high-voltage eV-resolution (HVeV) detector. Data were taken underground in the NEXUS facility located at Fermilab with an overburden of 225 meters of water equivalent. The experiment benefits from the minimizing of luminescence from the printed circuit boards in the detector holder used in all previous HVeV studies. A blind analysis of $6.1\mathrm{g}·\mathrm{days}$ of exposure produces exclusion limits for dark matter-electron scattering cross sections for masses as low as $1\mathrm{MeV}/c^2$, as well as on the photon-dark photon mixing parameter and the coupling constant between axionlike particles and electrons for particles with masses $>1.2\mathrm{eV}/c^2$ probed via absorption processes.

We propose an experiment to test the nonclassicality of the gravitational interaction. We consider two optomechanical systems that are perfectly isolated, except for a weak gravitational coupling. If a suitable resonance condition is satisfied, an optical signal can be transmitted from one system to the other over a narrow frequency band, a phenomenon that we call gravitationally induced transparency. In this framework, the challenging problem of testing the quantum nature of gravity is mapped to the easier task of determining the nonclassicality of the gravitationally induced optical channel: If the optical channel is not entanglement-breaking, then gravity must have a quantum nature. This approach is applicable without making any assumption on the (currently unknown) correct model of gravity in the quantum regime. In the second part of this work, we model gravity as a quadratic Hamiltonian interaction (e.g., a weak Newtonian force), resulting in a Gaussian thermal attenuator channel between the two systems. Depending on the strength of thermal noise, the system presents a sharp transition from an entanglement-breaking to a nonclassical channel capable not only of entanglement preservation but also of asymptotically perfect quantum communication.

The Euclidean path integral approach to quantum gravity is conventionally formulated in terms of the Einstein-Hilbert-York-Gibbons-Hawking action, which requires suitable subtractions to produce the correct black hole partition function. However, there is a unique, canonical teleparallel reformulation which reproduces the same results without subtractions or other ambiguities. This is verified in the case of a black hole with or without an electric or a magnetic charge and in a background with or without a cosmological constant. Moreover, a new quasilocal prescription is proposed and tested, where the black hole partition function is determined solely by the horizon boundary term, yielding the correct Helmholtz free energy without counterterms.

The $U(1)$ $CP$-violating phase which arises below chiral symmetry breaking in a non-Abelian gauge theory is “secretly” the magnetic dual of the flux of a $U(1)$ 4-form gauge field. Thus, the discharge of this 4-form flux by Schwinger production of charged membranes reduces the total $CP$-violating phase toward zero. This can safely restore $CP$ symmetry to within the observational limits, ${\theta }_{\cancel{\mathtt{CP}}}\lesssim {10}^{-10}$, while also satisfying all limits from cosmology, when the charge and the tension of the gauge field sources are in the $\lesssim \mathrm{keV}$ range.

We present a novel determination of the down-to-up quark composition ratio using the forward-backward asymmetry observed in the proton-proton collisions at the LHC. This method offers unique insights into the flavor-specific difference between down and up quarks, which are difficult to isolate in traditional cross-section measurements due to the inherent mixing of contributions from both flavors. In this study, we systematically measure the down-to-up quark ratio over a broad momentum fraction ($x$) range of 0.01 to 0.1, utilizing the sensitivity of the forward-backward asymmetry to quark-level couplings. Our findings reveal significant deviations in both the value and $x$ dependence of this ratio compared to predictions from current parton distribution functions. These discrepancies highlight potential limitations in existing parton distribution function parametrization and emphasize the importance of flavor-separated measurements for advancing our understanding of proton structure.

Although discovered more than sixty years ago, direct measurement of the $K^{*}(892)\to K\pi$ branching fractions is a formidable challenge that has not been attempted. Typically they are assumed to obey the isospin limit in hundreds of particle data measurements. We show that an abundance of recent amplitude analyses and other data, however, enables recovery of the ratios $\mathcal{B}(K^{*+}\to K^{+}{\pi }^0)/\mathcal{B}(K^{*+}\to K_S^0{\pi }^{+})$ and $4\mathcal{B}(K^{*0}\to K_S^0{\pi }^0)/\mathcal{B}(K^{*0}\to K^{+}{\pi }^{-})$ at $\sim 5\%$ precision.

We analyze the physical properties of an analytical, nonsingular quantum-corrected black hole solution recently derived in a minisuperspace model for unimodular gravity under the assumption of unitarity in unimodular time. We show that the metric corrections compared to the classical Schwarzschild solutions only depend on a single new parameter, corresponding to a minimal radius where a black hole-white hole transition occurs. While these corrections substantially alter the structure of the spacetime near this minimal radius, they fall off rapidly toward infinity, and we show in various examples how physical properties of the exterior spacetime are very close to those of the Schwarzschild solution. We derive the maximal analytic extension of the initial solution, which corresponds to an infinite sequence of Kruskal spacetimes connected via black-to-white hole transitions, and compare with some other proposals for nonsingular black hole metrics. The metric violates the achronal averaged null energy condition, which indicates that we are capturing physics beyond the semiclassical approximation. Finally, we include some thoughts on how to go beyond the simple eternal black hole-white hole model presented here.

We present evidence for a spatially modulated instability within the deconfined quark-gluon plasma phase of QCD, based on robust predictions from holographic models. In these models, which are accurately fitted to lattice data, the instability is driven by the Chern-Simons term mandated by the flavor anomalies of QCD. Such an instability occurs universally across holographic models at surprisingly low densities, within the crossover region amenable to lattice and experimental studies, therefore inviting further explorations of inhomogeneous phases in this region.

In this study, we investigate the effect of energy-momentum squared gravity (EMSG) on the curvature of neutron stars (NSs) by using three relativistic mean-field (RMF) equations of state (EOSs) and three hadron–quark phase transition (HQPT) EOSs. Neutron stars, with their extreme densities and strong gravitational fields, provide an ideal laboratory for testing general relativity (GR) in the high-curvature regime and for exploring possible deviations via modified gravity. EMSG extends GR by including nonlinear terms involving the energy-momentum tensor, characterized by a coupling parameter $\alpha$. We focus on the Kretschmann, Ricci, and Weyl curvature scalars, analyzing their dependence on baryon density and radial coordinate for varying values of $\alpha$. Our results indicate that EMSG can significantly alter the curvature profiles of neutron stars. In particular, the magnitude of both Weyl and Kretschmann scalars increases (decreases) for a positive (negative) EMSG parameter, with the former exhibiting a larger dependence. Similarly, the surface curvature (SC) is notably affected by $\alpha$. Interestingly, we further observe distinct discontinuities in the curvature profiles at hadron-quark phase transitions, especially in the soft and intermediate HQPT models. These signatures may provide observable imprints of exotic core phases in neutron stars.

In this work, we develop the modified Teukolsky formalism that describes the gravitational wave (GW) radiation from a point mass orbiting around a perturbed Schwarzschild black hole. This perturbation of the background spacetime induces a secular change in the orbital phase of the point mass. In turn, this causes a modification in the GW flux, which can be used to probe the background spacetime. We explicitly apply this formalism to a bumpy Schwarzschild spacetime as a proof of principle. The results pave the way for the description of extreme mass-ratio inspirals in generic perturbed Kerr spacetime in future developments.

We report the existence of two exotic compact objects in the leading relativistic model of modified Newtonian dynamics, namely æther-scalar-tensor theory. This model is consistent with precision cosmology and gravitational wave constraints on tensor speed. Black hole mimickers could subtly change observations: gravitational waves from their mergers might show unusual echoes or altered ringdown patterns, and images of their horizon-scale shadows might be slightly different from those of a true black hole. Shapiro-free lenses are massless objects that deflect light without any gravitational time delay, producing distinctive lensing events. These predictions connect to ongoing and future gravitational-wave searches, horizon-scale imaging, and time-domain lensing surveys.

Gravitational lensing is a powerful probe of cosmology and astrophysics. With the prospect of the first strongly lensed gravitational waves on the horizon, we highlight an opportunity to test fundamental physics. In this work, we assume a nonzero mass for the graviton, which leads to gravitational waves following timelike geodesics instead of null geodesics. We derive standard gravitational lensing equations, such as the scattering angle, the time delay between different images, and the magnification, which normally rely on the assumption of null geodesics. We show that a single strongly lensed multimessenger event is enough to constrain the graviton mass to $m<3\times {10}^{-23}\mathrm{eV}/{\mathrm{c}}^2$. Notably this constraint is independent of the lens model, of the waveform model, and of cosmology. Additionally, we explore magnification of images and find that they offer at least 3 orders of magnitude weaker bounds than the time delay, and have a dependence on the correct modeling of the lens and cosmology.

Black holes in four-dimensional, asymptotically flat general relativity have vanishing static tidal Love numbers (TLNs), a property tied to a hidden symmetry of the perturbation equations. Within the Konoplya-Rezzolla-Zhidenko (KRZ) parametrization, a subclass of spacetimes was previously shown to admit such ladder symmetry, which enforces the absence of static scalar TLNs. In this work, we introduce parametric deformations to such ladder-symmetric spacetimes and analyze the resultant linear tidal response. Using the parametrized formalism for TLNs, we show that any deviation from a ladder-symmetric background leads to nonzero static scalar TLNs. This establishes ladder symmetry as a necessary, as well as sufficient condition for the vanishing of static TLNs in static, spherically symmetric black holes and in rotating black holes of the KRZ class.

We study the gravitational microlensing of various static and spherically symmetric nonsingular black holes (and horizonless, nonsingular compact objects of similar size). For pointlike sources we extend the parametrized post-Newtonian lensing framework to fourth order, whereas for extended sources we develop a ray tracing approach via a simple radiative transfer model. Modelling nonrelativistic proper motion of the lens in front of a background star we record the apparent brightness as a function of time, resulting in a photometric lightcurve. Taking the star radius to smaller values, our numerical results approach the theoretical predictions for pointlike sources. Compared to the Schwarzschild metric in an otherwise unmodified lensing geometry, we find that nonsingular black hole models (and their horizonless, nonsingular counterparts) both at finite size and for point lenses tend to feature larger magnifications in microlensing lightcurves.

We present a complete computation of the scalar power spectrum in the inflation without inflaton (IWI) framework, where the inflationary expansion is driven solely by a de Sitter (dS) background and scalar fluctuations arise as second-order effects sourced by tensor perturbations. By explicitly deriving and numerically integrating the full second-order kernel of the Einstein equations, we obtain a scale-invariant scalar spectrum without invoking a fundamental scalar field. In this framework, the amplitude of the scalar fluctuations is directly linked to the scale of inflation. More precisely, we show that matching the observed level of scalar fluctuations ${\mathrm{\Delta }}_{\mathcal{\varphi }}^2(k_{*})\approx {10}^{-9}$ at cosmic microwave background scales fixes the inflationary energy scale $H_{\inf }$ as a function of the number of observed e-folds $N_{\mathrm{obs}}$. For $N_{\mathrm{obs}}\simeq 30–60$, we find $H_{\inf }\simeq 5\times {10}^{13}\mathrm{GeV}–2\times {10}^{10}\mathrm{GeV}$, corresponding to a tensor-to-scalar ratio $r\simeq 0.01–5\times {10}^{-9}$. In particular, requiring consistency with instantaneous reheating, we predict a number of e-foldings $\mathcal{O}(50)$ and an inflationary scale $H_{\inf }\simeq {10}^{11}\mathrm{GeV}$. We also incorporate in our framework the quantum break time of the dS state, and we show that it imposes an upper bound on the number of particle species. Specifically, using laboratory constraints on the number of species limits the duration of inflation to $N_{\mathrm{obs}}\lesssim 126$ e-folds. These results establish the IWI scenario as a predictive and falsifiable alternative to standard inflaton-driven models, linking the observed amplitude of primordial fluctuations directly to the quantum nature and finite lifetime of dS space.

The exponential-tail behaviors of the probability density function (PDF) of the primordial curvature perturbation are confirmed in the mild-waterfall variants of hybrid inflation with the use of the stochastic formalism of inflation. On top of these tails, effective upper bounds on the curvature perturbation are also observed, corresponding to the exact hilltop trajectory during the waterfall phase. We find that in the model where the leading and higher-order terms in the expansion of the inflaton potential around the critical point are fine-tuned to balance, this upper bound can be significantly reduced, even smaller than the primordial black hole (PBH) threshold, as a more novel perturbation-reduction mechanism than the one proposed by Tada and Yamada. It makes PBH formation much more difficult compared to the Gaussian or exponential-tail approximation. We also introduce Johnson’s $S_U$ distribution as a useful fitting function for the PDF, which reveals a nonlinear mapping between the Gaussian field and the curvature perturbation.

Current cosmological data seem to show that dark energy is evolving in time and that it possibly crossed the phantom divide in the past. So far the only theories that lead to such a behavior involve a nontrivial coupling between dark energy, in the form of a scalar field, and the gravitational or matter sector. We show that there is another possibility involving both a nontrivial kinetic sector in a cubic Galileon theory and a scalar field potential that breaks the Galileon shift symmetry, which can lead to a similar phenomenology on large scales. We perform a full Bayesian analysis using the latest cosmological data, including DESI DR2 baryonic acoustic oscillation measurements, type Ia SNe measurements from DESY5, Union3, and Pantheon+, and cosmic microwave background data from Planck and ACT. We find that it is statistically strongly favored over a universe dominated by a cosmological constant (with a Bayes factor of $\log B\simeq 6.5$). Yet, as with other nonminimally coupled theories, it has severe ancillary gravitational effects. These can be mitigated to some extent, but as with other viable theories, the penalty is ever more elaborate scalar field models of dark energy.