We propose Bell-type inequalities by constructing flavor operators associated with mass identification, flavor change, and charged-current weak mixing which arise from fundamental interactions in the Standard Model. We treat these interactions as measurement settings in a gedanken experiment. For entangled two-particle states, the measurement outcomes of these flavor operators exhibit correlations that violate a Bell-type inequality under the stated assumptions, showing that our result probes contextuality and incompatibility of interaction-defined observables. We discuss how the predicted correlation patterns may be probed with experimental data, clarifying the scope and limitations of Bell-type reasoning in particle physics.

Superallowed ($0^{+}\to 0^{+}$) beta decays currently provide the most precise extraction of quark mixing in the Standard Model. Their interpretation as a measurement of $|V_{ud}|$ relies on a reliable first-principles computation of QED radiative corrections expressed as a series in $Z\alpha$ and $\alpha$. In this work, we provide the first model-independent result for two-loop, $O(Z{\alpha }^2)$, long-distance radiative corrections where the nuclei are treated as heavy pointlike particles. We use renormalization group analysis to obtain new results at $O(Z{\alpha }^3)$ for the coefficient of double logarithms in the ratio of the maximal beta energy to the inverse nuclear size, $E_m/R^{-1}$. We use the Kinoshita-Lee-Nauenberg theorem to obtain new results at $O(Z^2{\alpha }^3)$ for the coefficient of logarithms in the ratio of maximal beta energy to the electron mass, $\log (2E_m/m)$. We identify a structure-dependent, and, therefore, short-distance, contribution to the traditional $Z{\alpha }^2$ correction that should be revisited. We provide the first comprehensive update to the long-distance corrections in almost 40 years and comment on the impact of our findings for extractions of $|V_{ud}|$. We find that shifts in the long-distance corrections are $2.5\times$ larger than past estimates of their uncertainty, $1.5\times$ larger than the statistical uncertainty from the combined fit of superallowed decays, and about $1/2$ the size of estimated systematic error, which stems dominantly from nuclear structure effects.

Detection of entanglement through the Newtonian potential has been claimed to support the existence of gravitons, by extrapolating to a thought experiment which demonstrates that complementarity and causality would be in conflict unless quantum fluctuations exist. We critically assess this consistency argument using scalar field models. We show that whether complementarity or no-signaling is violated when quantum fluctuations are neglected, depends on how this approximation is taken, while in both cases entanglement is generated locally in spacetime. We clarify that the correct reading of the paradox requires making a clear distinction between two notions of causality violation: Newtonian action-at-a-distance and quantum mechanical signaling at spacelike separation; the latter is pertinent while the former is not. We conclude that the thought experiment (a) does not add to the epistemological relevance of entanglement through Newtonian potentials (b) lends support for the existence of gravitons, if retardation effects are detected in entanglement through gravity.

We provide a detailed analysis of the nontwisting subcase of the large class of type D black holes with a nonaligned electromagnetic field, presented recently in H. Ovcharenko and J. Podolský [Phys. Rev. D 112, 064076 (2025)]. We show that such exact solutions split into two main subclasses that (after a suitable reparametrization) can be interpreted as either the uncharged Schwarzschild or C-metric in the external Bertotti-Robinson (BR) spacetime with geometry ${\mathrm{AdS}}_2\times {\mathrm{S}}_2$, or as the charged Reissner-Nordström black hole accelerating in the external BR electromagnetic field. The distinction between these two subclasses is determined by the parameter $r_0$ that encodes relations between the external Maxwell field (given by the nonaligned components of the Faraday tensor ${\mathrm{\Phi }}_0$, ${\mathrm{\Phi }}_2$) and the Maxwell field created by the charge of the black hole (given by the aligned component ${\mathrm{\Phi }}_1$). Namely, if $r_0=0$ then the electromagnetic field is fully determined by ${\mathrm{\Phi }}_0={\mathrm{\Phi }}_2$, and one gets the C-metric in the BR universe (including also the nonaccelerating Schwarzschild-BR black hole). But if $r_0\ne 0$ then the electromagnetic field is independently determined by both the external BR field and the field of a black hole itself, and this can be interpreted as the Reissner-Nordström black hole accelerating in the Bertotti-Robinson spacetime. Even though such an interpretation of the spacetime family is quite simple, it contains a lot of subtleties (e.g. the no-charge limit of the RN-BR spacetime, the nontrivial dependence on the signs of the mass and charge of a black hole, extreme black holes, and others) which we carefully investigate in this work. We also show the explicit relation to solutions previously found by Van den Bergh and Carminati, and we discuss the connection to the Alekseev-Garcia and Alexeev solutions.

We derive the Hamiltonian for general semiclassical 2D dilaton gravity, beginning with the complete action including the Polyakov action and Gibbons-Hawking-York boundary term. The value of the Hamiltonian yields a generalized Brown-York quasilocal mass function, and the Arnowitt-Deser-Misner and Bondi masses are obtained in the appropriate limits. The Bondi mass is equal to the classical mass plus a correction term given by the transformation between initial and final inertial frames. We test the expression for the Bondi mass in the Russo-Susskind-Thorlacius model, which can be treated analytically, and in several other models numerically. We find it is monotonically decreasing and remains positive throughout the evaporation process for asymptotically flat black holes.

The Galactic diffuse gamma-ray emission is conventionally modeled as the product of cosmic-ray interactions with the interstellar medium. However, the cumulative contribution of stellar atmospheres acting as hadronic interaction targets remains an unexplored multimessenger background. In this work, we present the first systematic evaluation of this stellar diffuse emission by coupling MESA stellar evolution profiles and magnetic-field-modulated cosmic-ray transport with a 3D Galactic population synthesis framework. We find that the cumulative stellar contribution to the Galactic diffuse gamma-ray flux is negligible at 1 TeV, and the associated diffuse neutrino flux ($\sim {10}^{-17}\mathrm{TeV}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$) remains orders of magnitude below current IceCube limits. Nevertheless, at ultrahigh energies ($>10\mathrm{TeV}$), this emission establishes an irreducible local background that overtakes the strongly attenuated extragalactic isotropic gamma-ray background. Our results demonstrate that the Galactic stellar ensemble is a strictly subdominant background, indicating that stellar subtraction templates are not required for identifying Galactic PeVatrons or constraining dark matter annihilation.

Observations of supermassive black holes (SMBHs) at high redshifts challenge standard seeding scenarios. We examine a dissipative self-interacting dark matter (dSIDM) model in which gravothermal collapse leads to the formation of massive BH seeds ab initio. We utilize a semianalytical framework to predict properties of the dSIDM-seeded SMBH population. Billion solar mass quasars are reproduced along with low-mass faint active galactic nuclei (known as little red dots) with SMBH-to-galaxy stellar mass ratios consistent with recent James Webb Space Telescope observations. To match the abundance of the observed bright quasars, a subpercent-level duty cycle is suggested, implying a large population of dormant SMBHs. The gravitational wave (GW) signals from mergers of these massive SMBHs can be detected by LISA while remaining within the NANOGrav constraints on the GW background. These results provide testable signatures of DM-driven SMBH formation, offering a pathway to probe hidden-sector physics through SMBH and GW observables.

We develop an accurate simulation-based inference framework for high-mass ($\gtrsim {10}^7{\mathrm{M}}_{\odot }$) black-hole binaries observable by LISA. The method is implemented within the dingo gravitational-wave parameter-estimation code, extending its application from ground-based detectors to the LISA band. We train a normalizing-flow model using aligned-spin higher-mode waveform models and a low-frequency approximation of the detector response at fixed reference time. After sampling, we importance sample to the true posterior based on the underlying likelihood and prior. We validate performance on simulated signals spanning the signal-to-noise regimes relevant for LISA observations and benchmark our new dingo implementation against standard methods. We report robust agreement in the inferred posterior distributions up to signal-to-noise ratios of $\sim 500$. At higher signal-to-noise ratios of $\sim 1000$, we observe a reduction in sampling efficiency, while still yielding unbiased and tightly localized posteriors that can be used as a starting point for follow-up with traditional methods. The trained flow can generate 20 thousand posterior samples in less than a minute, establishing dingo as a promising neural inference framework for rapid full-parameter estimation of massive black-hole binaries in the LISA band. The proposed approach allows for straightforward generalizations, including a time-dependent detector response, nonstationary noise artifacts such as gaps and glitches, and low-latency parameter estimations.

We present a search for gravitational waves from inspiraling, planetary-mass ultracompact binaries using data from the first part of the fourth observing run of LIGO, Virgo, and KAGRA. Finding no evidence of such systems, we determine the maximum distance reach for such objects and their merger rate densities. Then, we identify classes of primordial black hole mass distributions for which these rate limits can be translated into relevant constraints on the mass distribution of primordial black holes, assuming that they are all composed of dark matter, in the mass range $[{10}^{-6},{10}^{-3}]M_{\odot }$. Our constraints for the class of primordial black hole mass distribution functions $f(m)$ we consider reach down to $f(m)\sim 0.1$. They are consistent with existing microlensing results in the planetary-mass range, provide a complementary probe to subsolar mass objects, and are publicly available [1].

The evolution of the vacuum state in a time-dependent external electric field of arbitrary polarization is investigated within a nonperturbative framework of quantum kinetic equations (QKEs). In our previous work [Phys. Rev. Res. 6, 043009 (2024)], a revised version of the QKEs was derived by using an adiabatic basis constructed from one-particle Hamiltonian eigenfunctions in a spatially homogeneous electric field. In this study, we present an extensive analysis of these equations with particular emphasis on observable quantities. The focus of the present work is therefore not on a rederivation of asymptotic pair-production spectra for special pulses, but on a self-contained construction of basis-independent observables and their renormalization in a matrix-valued QKE formulation valid for arbitrary polarization. Specifically, we compute momentum-resolved particle yields, the induced electron-positron current, the energy-momentum tensor, and the angular-momentum tensor. In the linear-polarization limit these observables reduce to known QKE expressions; here they are constructed explicitly for the corrected QKE system at arbitrary polarization, with circularly polarized fields included as a special case. We also discuss in detail the charge-renormalization procedure required to remove logarithmic divergences. It is shown that our results are consistent with the previous findings obtained via the Dirac-Heisenberg-Wigner formalism. Our analysis provides a firmer theoretical basis for investigations of nonperturbative effects in strong electric fields.

We calculate the terrestrial, astrophysical, and cosmological constraints on a light vector boson that couples to an arbitrary combination of the electromagnetic and $B-L$ currents of the Standard Model. The dark photon and a vector boson coupling to $B-L$ are special cases of our generalized flavor-universal anomaly-free vector boson, requiring just one additional parameter (the “dark mixing angle” corresponding to the linear combination of the electromagnetic and $B-L$ currents) beyond that of the overall coupling strength and the vector boson mass, where we focus on the range 1 MeV to 60 GeV We perform a detailed investigation of a unique combination where the vector boson couplings to electrically charged leptons and protons are highly suppressed: the “chargephobic dark photon.” A chargephobic vector boson is very weakly constrained by current terrestrial experiments including beam dumps and collider experiments, since they rely on couplings to electrons and protons. Instead, neutrino scattering experiments (such as COHERENT), astrophysical sources (supernova emission), and cosmology ($\mathrm{\Delta }{N}_{\mathrm{eff}}$) provide the strongest constraints due to the nonzero couplings of the chargephobic vector boson to neutrinos and neutrons. Indeed, we find that supernova emission and $\mathrm{\Delta }{N}_{\mathrm{eff}}$ provide constraints throughout the space of dark mixing angles, demonstrating their importance to provide model-independent constraints. For nearly all of the parameter space, a chargephobic vector boson is the most weakly constrained anomaly-free vector boson that couples to flavor-independent or flavor-dependent combinations of Standard Model currents. Finally, we highlight the importance of future experiments, including SHiP, that are able to probe new regions of the chargephobic parameter space due to the significantly improved detector capabilities.

The simplified template cross section (STXS) program has become the standard interface between Higgs measurements and global fits, but its fixed one-dimensional boundaries are not guaranteed to align with the phase-space directions to which the Standard Model effective field theory (SMEFT) is most sensitive. We propose a machine-learning-inspired extension of STXS in which supervised classifiers are used only at the design stage to identify simple, publishable phase-space boundaries. Using associated Higgs production, $pp\to ZH$, as a case study and a benchmark momentum-dependent bosonic SMEFT deformation, we show that the relevant signal-background separation is well captured by a linear boundary in the $(p_T^Z,m_{ZH})$ plane. We construct such boundaries with a linear support vector machine and with a deep-neural-network-assisted distillation procedure, and compare them directly with the standard STXS $p_T^Z$ bins through a common single-region Asimov-significance analysis. In this proof-of-concept setup, the machine-learning-inspired regions systematically outperform the corresponding STXS regions, with the largest gains appearing in the boosted regime where SMEFT effects are concentrated. The final observable remains a simple linear cut, preserving the transparency and experimental portability that make STXS useful.

The doubly charmed tetraquark $T_{cc}$ was reported by the LHCb experiment in 2022 and a lot of theoretical studies have been conducted. The small binding energy measured from the $D^{*+}{D}^0$ threshold indicates that $T_{cc}$ is a $D{D}^{*}$ molecule. On the other hand, the superflavor symmetry, which relates heavy antiquarks to heavy diquarks, provides a useful framework for predicting the existence of partner exotic hadrons associated with $T_{cc}$. By replacing ${\overline{D}}^{(*)}$ with ${\mathrm{\Xi }}_{cc}^{(*)}$ within this symmetry, ${\overline{D}}^{(*)}{\mathrm{\Xi }}_{cc}^{(*)}$ and ${\mathrm{\Xi }}_{cc}^{(*)}{\mathrm{\Xi }}_{cc}^{(*)}$ are expected to form partner structures of $T_{cc}$. In this paper, we investigate bound and resonant states of ${\overline{D}}^{(*)}{\mathrm{\Xi }}_{cc}^{(*)}$ and ${\mathrm{\Xi }}_{cc}^{(*)}{\mathrm{\Xi }}_{cc}^{(*)}$ based on the one boson exchange potential, where $\pi$, $\rho$, $\omega$, and $\sigma$ are considered as bosons. The cutoff parameter and the coupling constants for ${\overline{D}}^{(*)}{\mathrm{\Xi }}_{cc}^{(*)}$ and ${\mathrm{\Xi }}_{cc}^{(*)}{\mathrm{\Xi }}_{cc}^{(*)}$ are taken to be the same as those for $T_{cc}$ due to superflavor symmetry. We also discuss the $\sigma$ coupling constant, which is uncertain, dependence of these mass spectra. A lot of bound and resonant states with some quantum numbers are obtained for each $\sigma$ coupling constant, but these mass spectra depend on the $\sigma$ coupling constant significantly.

We take a step toward a “microscopic” derivation of gauge-string duality. In particular, using mathematical techniques of Strebel differentials and discrete exterior calculus, we obtain bosonic string worldsheet action for string embedded in $\mathrm{d}+1$-dimensional asymptotically anti–de Sitter space from multiloop Feynman graphs of quantum field theory of scalar matrices in d-dimensions in the limit of diverging loop number. Our work is building on the program started by ’t Hooft in 1974, this time including the holographic dimension, which we show to emerge from the continuum of Schwinger parameters of Feynman diagrams.

Codimension-two vortex solutions are important solitonic objects in both quantum field theory and gravity. In this paper, we construct a class of codimension-two Alice-vortex solutions in axio-dilaton gravity, in which monodromy around the vortex enacts the axion transformation $C_0\mapsto -C_0$. In IIB supergravity, this furnishes a class of R7-brane backgrounds of the sort predicted by the swampland cobordism conjecture. Such configurations generically carry an intrinsic dipole moment. We extract additional properties of such branes from scattering probes. These results provide further evidence that the world-volume theory of an R7-brane is an eight-dimensional nonsupersymmetric interacting quantum field theory.

Gibbons and Hawking proposed that the Euclidean gravity path integral with periodic boundary conditions in time computes the thermal partition sum of gravity. As a corollary, they argued that a derivative of the associated free energy with respect to the Euclidean time period computes gravitational entropy. Why is this interpretation correct? That is, why does this path integral compute a trace over the Hilbert space? Here, we show that the quantity computed by the Gibbons-Hawking path integral is equal to an a priori different object—an explicit thermal trace over the Hilbert space spanned by states produced by the Euclidean gravity path integral. This follows in two ways; (a) if the Hilbert space with two boundaries factorizes into a product of two single boundary Hilbert spaces, as we have previously shown, and (b) via explicit resolution of the trace by a spanning basis of states. We similarly show how a replicated Euclidean gravity path integral with a single periodic boundary computes a Hilbert space trace of powers of the density matrix, explaining why this approach computes the entropy of states entangled between two universes.

Radially symmetric non-BPS ’t Hooft-Polyakov monopoles and dyons are constructed as resurgent transseries: infinite sums of exponentially decaying terms, each multiplied by a factorially divergent fluctuation factor. All higher exponential terms are explicitly expressed in terms of the leading order solutions. In the BPS limit all fluctuation terms truncate.

Triple systems have progressively been recognized as ubiquitous in our Universe and provide a good testing ground for wave generation and propagation in nontrivial environments. We study the dynamics of triple systems in a fully nonlinear setting. In particular, we analyze numerical relativity simulations of head-on collisions of black holes in the presence of a companion. We show evidence for Doppler and gravitational redshift in the ringdown, and clear signs of amplification by lensing. In certain cases, we also show the appearance of a second image, with hints of resonant mode excitation. Our results pave the way for the understanding of mergers in the vicinity of massive companions. Even in extreme setups we do not find collapse to black holes from lensed gravitational radiation.

We investigate the frame dependence of the bound on the Lyapunov exponent for charged particles in the dilatonic Reissner-Nordström-anti–de Sitter (AdS) and Kerr-Sen-AdS black hole backgrounds, derived from the Einstein-Maxwell-dilaton theory and the low-energy effective action of heterotic string theory, respectively. A parallel analysis is performed across both the Einstein and string (Jordan) frames to examine the influence of the choice of frame on chaotic behavior. For massless particles, the Lyapunov exponent remains invariant under frame transformations, whereas for massive particles, it exhibits frame dependence owing to its coupling to the dilaton field. Our results demonstrate that the bound on chaos is not frame invariant and depends on the choice of frame. Depending on the various parameters, the bound can be satisfied in the Einstein frame and violated in the string frame, whereas the opposite situation may occur for different parameter values. Numerical computations corroborate the analytical findings and reveal the modifications in the chaotic behavior of string-inspired black holes induced by the dilaton field and the choice of frame.

Gravitational-wave observations of binary neutron star systems can shed light on the currently unknown dense matter equation of state. The equation of state determines a large number of neutron star properties, such as tidal deformability, radius, and quadrupole moment, several of which directly affect the emitted gravitational-wave signals. To reduce the dimensionality when computing gravitational waves and when interpreting observational data, quasiuniversal relations are commonly employed to connect different neutron star properties. However, quasiuniversal relations are not exact, and their use may introduce uncertainty and bias. We explore the potential biases arising from different quasiuniversal relations in the third-generation era: (i) the Love-Q relation connecting the spin-induced quadrupole moment and the tidal deformability, (ii) the relation between the fundamental mode frequency and the tidal deformability, and (iii) the binary Love relation. We find that for the quadrupole relation biases are only present for rapidly rotating systems, for the binary-Love relation induces moderate biases only in the next-to-leading-order tidal parameters, which can, however, propagate into the inferred equation of state at low masses. Regarding fundamental mode frequencies, we find that the employed relation introduces only negligible biases, while waveform systematic effects can become comparatively large. Our results highlight that, while quasiuniversal relations remain a useful tool within gravitational-wave analyses, careful treatment is needed to avoid biases in equation-of-state measurements with next-generation detectors.