For both theoretical and phenomenological studies, it is important to analyze the function types of Feynman integrals. The phenomenon of genus drop between different representations of hyperelliptic Feynman integrals was discussed in [1]. In this paper, we reformulate the extra-involution mechanism of [1] as a special case of an unramified double covering between algebraic curves, and show that this covering mechanism also explains genus drops accompanied by a curve-type change from nonhyperelliptic to hyperelliptic for a class of three-loop Feynman diagrams. We also demonstrate that within a specific framework, the origin of the discrete spacetime symmetry that leads to the genus drop in hyperelliptic cases is manifest. This work also points out that there exist nonhyperelliptic Feynman integrals that exhibit no apparent genus drop.

Inspired by the latest BESIII measurement of the $\mathrm{\Lambda }(1520)\to \gamma {\mathrm{\Sigma }}^0$ radiative decay, we systematically study the decays $\mathrm{\Lambda }(1520)\to \gamma \mathrm{\Lambda }({\mathrm{\Sigma }}^0)$ within the chiral unitary approach, where the $\mathrm{\Lambda }(1520)$ is treated as a dynamically generated resonance from meson-baryon interactions. Compared with previous chiral unitary studies, we adopt dimensional regularization for $S$-wave loop integrals to preserve gauge invariance and, for the first time, include Feynman diagrams with photon coupling to intermediate baryons. Our calculated partial decay width $\mathrm{\Gamma }(\mathrm{\Lambda }(1520)\to \gamma {\mathrm{\Sigma }}^0)$ agrees well with the new BESIII data, whereas the predicted $\mathrm{\Gamma }(\mathrm{\Lambda }(1520)\to \gamma \mathrm{\Lambda })$ is considerably smaller than the CLAS experimental result. By comparing our results with predictions from various quark models, together with an analysis of the $\mathrm{\Lambda }(1520)$ compositeness, we discuss the internal nature of the $\mathrm{\Lambda }(1520)$ resonance, highlight its complex component structure, and stress the need for more refined theoretical frameworks and further experimental measurements.

We study the cosmology and observational probes of majoron dark matter in a high-scale seesaw framework with spontaneously broken lepton number. Right-handed neutrinos naturally generate light neutrino masses and can realize thermal leptogenesis, while the associated majoron is a light pseudo-Nambu-Goldstone boson that can be cosmologically stable and serve as a viable dark matter candidate for sub-MeV masses. We analyze both preinflationary and postinflationary histories of lepton number breaking. In the preinflationary scenario, majoron dark matter is produced by misalignment and constrained by CMB isocurvature. In the postinflationary scenario, the majoron abundance receives nonthermal contributions from spatially averaged misalignment, majoron radiation from global cosmic strings, and the collapse of the string-domain wall network, as well as a thermally produced component. This scenario can also be probed by future searches for the stochastic gravitational wave background produced by cosmic strings. We map the viable majoron dark matter parameter space and examine complementary probes from x-ray and soft $\gamma$-ray searches for majoron decays to photons, black hole superradiance, and Lyman-$\alpha$ forest observations. These results demonstrate that majoron dark matter offers a distinctive cosmological probe of high-scale lepton number breaking and thermal leptogenesis.

We demonstrate that TeV-scale heavy neutral leptons (HNLs) responsible for inverse-seesaw neutrino mass generation can simultaneously fix the cosmological abundance and decay properties of dark matter (DM). The spontaneous breaking of lepton number gives rise to a pseudo-Nambu-Goldstone boson that serves as a light DM candidate, whose mass originates from a small explicit symmetry-breaking term. The same HNLs that generate neutrino masses produce the DM via freeze-in and mediate its decay into neutrinos, leading to a tight correlation among neutrino masses, DM relic abundance, and DM lifetime. For collider-accessible TeV-scale HNLs, the observed relic density and lifetime constraints point to sub-GeV DM, yielding observable neutrino signals at JUNO and next-generation detectors such as Hyper-Kamiokande and DUNE. This framework establishes a predictive and experimentally testable link between neutrino mass generation and DM.

We deploy quantum chromodynamics in light-front quantization (and gauge), discretized and truncated in both Fock and momentum spaces with a particle-register encoding suited for quantum simulation; we show for the first time how to calculate fragmentation functions, a problem heretofore untractable in general from ab initio approaches. We provide a classical-simulator-based proof of concept by computing the charm-to-charmonium fragmentation, $c\to J/\psi$, in a simplified setup, an interesting case where we can (reasonably) compare with the known 1993 perturbative evaluation (and a more recent one at next-to-leading order) within nonrelativistic QCD.

We analyze the mixing between the ${\pi }^0$ meson and the photon in the presence of a strong uniform magnetic field, in the context of a two-flavor Nambu-Jona-Lasinio model. It is shown that only one specific photon polarization state can get mixed with the ${\pi }^0$ state, a fact that can be understood on general grounds. For magnetic fields with values up to $1{\mathrm{GeV}}^2/e$, it is found that the effect of the mixing on the pion mass and pion-quark couplings is relatively small (below a level of 15%), which is at variance with previous results reported in the literature.

A precision measurement of the $W$-boson production cross section is performed using the $W\to \mu \nu$ decay channel, based on a sample of proton-proton collision data collected by the LHCb experiment at $\sqrt{s}=13\mathrm{TeV}$ and corresponding to an integrated luminosity of $5.1{\mathrm{fb}}^{-1}$. The cross section is measured for muons with transverse momentum between 25 and 55 GeV and pseudorapidity between 2.0 and 4.5. The total production cross sections of $W$ bosons are measured to be ${\sigma }_{W^{+}\to {\mu }^{+}\nu }=1754.2\pm 1.5\pm 11.8\pm 35.1\mathrm{pb}$ ${\sigma }_{W^{-}\to {\mu }^{-}\overline{\nu }}=1178.1\pm 1.3\pm 9.7\pm 23.6\mathrm{pb}$ where uncertainties are statistical, systematic, and due to the luminosity determination, respectively. Differential distributions $\mathrm{d}{\sigma }_{W^{\pm }\to {\mu }^{\pm }\nu }/\mathrm{d}{\eta }^{{\mu }^{\pm }}$ are also presented. The total and differential cross sections are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. This measurement is significantly more precise than previous results in this kinematic regime.

We study duality-invariant higher-derivative corrections to the charged black hole geometry in two-dimensional heterotic string theory. We illustrate how the conventional perturbative approach to determine the corrected geometry breaks down. Using a nonperturbative (in ${\alpha }^{\prime }$) parametrization of the solution, we find the corrected charge-to-mass ratio for extremal black holes. We remark on the results in relation to the weak gravity conjecture. We also consider the entropy of the extremal black hole within the attractor mechanism and find that the two-derivative entropy is not renormalized to any order. We make comments on interpretations of the results and their extension to near-extremal black holes.

In this work we explore the relation between orbifold singularities and higher form symmetries. Using the geometric engineering dictionary, we argue that the discrete higher symmetries of 5D SCFTs constructed from M theory on a noncompact Calabi-Yau threefold can be related to a quantum symmetry of the associated BPS quiver. Through unorbifolding the quantum symmetry we obtain a new theory without higher form symmetry, providing a notion of “minimality” for a theory. This procedure is carried out via algebraic manipulations of the BPS/McKay quiver describing the crepant resolution of the singular geometry. This technique can also be reverted and thus, starting from any “minimal” theory, one can orbifold it and generate new theories with the desired higher form symmetries. We test our technology on classes of 5D SCFTs that arise from M-theory geometric engineering on Calabi-Yau threefolds that are nontoric noncomplete intersections, which have historically been challenging to tackle.

We perform a first-principles canonical quantization of a massive vector field, often referred to as the Proca field, in a Schwarzschild spacetime background. While scalar, fermionic, and electromagnetic fields are well studied in this context, the Proca field requires a more nuanced treatment because of the physical nature of the longitudinal polarization mode and the constrained dynamics of the field variables. By implementing the Dirac bracket formalism to treat the constraints inherent in the Proca action, we derive a consistent framework for the commutator algebra of creation and annihilation operators. Following this construction, we define the usual Boulware, Unruh, and Hartle-Hawking vacua. Using the Unruh vacuum, we derive and analyze the Hawking spectrum of the Proca field. Furthermore, we numerically evaluate the Proca condensate constructed from the two-point correlation function $⟨A_{\mu }(x)A_{\nu }(x^{\prime })⟩$, defined on all three vacuum states. We find that the condensate becomes significant near the boundary of the future horizon. Our results highlight the interplay among the different polarization modes and the significance of the Proca mass in quantum observables.

We investigate formulations of quantum field theories whose kinetic terms involve fractional or continuous powers of the d’Alembert operator. The primary requirements are perturbative unitarity and a well-defined classical limit with a finite number of initial conditions. A direct approach consists of continuing the correlation functions from Euclidean space to Minkowski spacetime using the fakeon prescription for the fractional part of the power. Alternative formulations arise through decomposition, in which the fractional part is represented as a continuum of ordinary fakeons. These options are infinite in number and yield inequivalent Minkowskian theories with the same Euclidean counterpart. We demonstrate these features at tree level and for bubble diagrams. We also point out potential pitfalls in the calculations. Finally, we show how to treat continuous powers of covariant d’Alembertians in fractional gauge and gravity theories. The Ward and Cutkosky identities hold in all formulations.

We consider a movable conducting plate of finite mass, between two fixed ones, whose mechanical degrees of freedom are treated quantum-mechanically and bound to its equilibrium position by a harmonic potential. The movable wall is thus subjected to quantum fluctuations of its position. This creates a system of two subcavities separated by the movable fluctuating plate, and two massless one-dimensional scalar fields, one in each subcavity. This system is described by an appropriate generalization of the Law Hamiltonian. The presence of the movable wall yields an effective plate-fields interaction, as well as an effective interaction between the field modes. We obtain, at the second order in perturbation theory, the ground state of the interacting system and the reduced density operator of the fields in each subcavity by tracing out the wall’s degrees of freedom. We calculate the entanglement between two field modes, one in each cavity, by evaluating analytically the negativity; we then also evaluate numerically the total multimode negativity. Our results show that in both cases the fields in the two subcavities are entangled, in contrast to the case in which the wall is fixed in space. We discuss the amount of the field entanglement present as a function of relevant physical parameters of the system such as the mass and oscillation frequency of the movable wall, its distance from the fixed walls and the frequencies of the field modes considered.

Time-dependent tidal interactions during the late inspiral of binary neutron stars encode valuable information about neutron-star structure, but systematically extending the familiar Newtonian mode-sum picture into full general relativity is nontrivial. In this paper, we develop a practical relativistic implementation of mode-sum tidal response for nonrotating neutron stars in Regge-Wheeler gauge. Using near-zone boundary conditions, we systematically define the interior tidal field, the relativistic overlap integrals, and the corresponding mode amplitudes. The good is that the dominant $f$-mode contribution is remarkably robust, reproducing the direct matching calculation to within $\sim 3\%$ across the equations of state we consider. The bad is that the operator governing mode inner product is not positive definite on the full Regge-Wheeler-gauge function space, so the relativistic mode sum truncated at $\mathcal{O}({\omega }^2)$ is not expected to strictly converge to the direct matching solution. The subtle is that the tidal field inside the star is not unique, although this ambiguity has only a limited impact on the dominant $f$-mode response for the classes of extensions studied here. Our results establish the practical utility of relativistic mode-sum approximations while making clear that their predictive power comes from a controlled low-mode description rather than from a formally convergent strong-field expansion.

Accurate modeling of gravitational-wave signals is essential for reliable inference of compact-binary source parameters, particularly for future space-based detectors operating in the milli- and deci-Hertz bands. In this work, we systematically investigate the parameter-estimation biases induced by neglecting orbital eccentricity when analyzing eccentric compact-binary coalescences with quasicircular waveform templates. Focusing on the deci-Hertz detector B-DECIGO and the milli-Hertz detector LISA, we model eccentric inspiral signals using a frequency-domain waveform that incorporates eccentricity-induced higher harmonics and the time-dependent response of spaceborne detectors. We quantify systematic biases in the chirp mass, symmetric mass ratio, and luminosity distance using both Bayesian inference and the Fisher-Cutler-Vallisneri (FCV) formalism, and assess their significance relative to statistical uncertainties. By constructing mock gravitational-wave catalogs spanning stellar-mass and massive black-hole binaries, we identify critical initial eccentricities at which systematic errors become comparable to statistical errors. We find that, for B-DECIGO, adopting a one-year observation period with $f_{\min }=0.1\mathrm{Hz}$, even very small eccentricities, $e_0\sim {10}^{-4}–{10}^{-3}$ at 0.1 Hz, can lead to significant biases, whereas for LISA, adopting a five-year observation period with $f_{\min }={10}^{-4}\mathrm{Hz}$, such effects typically arise at larger eccentricities, $e_0\sim {10}^{-2}–{10}^{-1}$ at ${10}^{-4}\mathrm{Hz}$, due to the smaller number of in-band cycles. Comparisons between FCV predictions and full Bayesian analyses show good agreement over most of the initial eccentricity range, but diverge at high eccentricity, where Bayesian inference is required. Our results highlight the necessity of incorporating eccentricity in waveform models for future space-based gravitational-wave observations.

The increasing scope and breadth of gravitational wave detectors is providing the opportunity to explore new parameters in gravitational-wave astronomy. Eccentricity and spin-precession are two key observables to infer the origin of a gravitational wave (GW) source. The interpretation of GW source parameters can be plagued by degeneracy, such as the well-known degeneracy between mass and spin. As the field has explored new parameters, questions have been raised about possible degeneracies between eccentricity and spin-precession. Although some state-of-the-art models now include these effects individually, models that incorporate spin-precession and eccentricity are only in their infancy. Until models faithfully cover the complete parameter space of compact binary coalescence, our ability to correctly measure the source parameters and infer the formation of the binary is compromised. Here, we present a study of the distinguishability of these two key parameters in heavy binary black hole systems. We study merger-ringdown dominated systems with detector-frame total masses ranging between $200-300M_{\odot }$ and mass ratio ranging between 1–3. Our work finds that there is indeed a degeneracy between eccentricity and spin-precession; however, it is a highly localized effect. We find that the misidentified eccentricity estimates get worse as the detector-frame total mass increases from $200M_{\odot }$ to $300M_{\odot }$, corresponding to progressively shorter signals in the detector band. Additionally, this misidentification is highly sensitive to the inclination angle of the source system. We provide quantifiable estimates of the potency of this degeneracy in addition to identifying some of the regions of parameter space where this degeneracy exists.

A common task in physics and astronomy is studying which of the competing hypotheses the data prefer. This is usually done by computing the Bayes factor between the two hypotheses and either interpreting it in terms of the posterior odds or as a ranking statistic for a frequentist p-value test. Here, we describe a relationship between the Bayes factor and its distributions under the two competing hypotheses, called the Bayes factor–Bayes factor (B-B) relationship, expressed as a diagnostic plot. Using examples from gravitational wave (GW) astronomy, we demonstrate how the B-B plot can validate the accuracy of Bayes factor calculations. The B-B relationship may also be useful for estimating background distributions of the Bayes factor at low computational cost, even analytically in some cases. We apply this technique in the context of wave-optics lensing of GWs, extrapolating the background distribution from GWTC4 to put a rough bound of $\lesssim 4.1\sigma$ on the statistical significance of the lensing hypothesis of GW231123.

We present imrphenomxhm_nsbh and seobnrv5hm_rom_nrtidalv3_nsbh, the first two frequency-domain models for gravitational-wave signals from quasicircular, aligned-spin neutron star-black hole binaries including higher-order modes beyond the dominant quadrupole. We also present imrphenomxphm_nsbh, an extension of the former model to the spin-precessing case. These models incorporate tidal effects in the gravitational-wave phasing and amplitude using a higher-mode extension of the NRTidalv3 model as well as dedicated amplitude models calibrated to numerical-relativity simulations of neutron star-black hole mergers. We test the performance and validity of the new models by comparing them to numerical-relativity simulations and other existing models for these systems. Finally, we perform parameter estimation studies. The new models show clear improvements over their predecessors in analyses of simulated signals while yielding results consistent with the literature when applied to real events from the GWTC-3 and GWTC-4 catalogs.

Chaos in extreme mass ratio inspirals is often thought to require unrealistically large secondary spins, making its astrophysical relevance uncertain. However, we find that chaos persists across the astrophysically realistic spin range for a spinning secondary orbiting a Schwarzschild black hole. This nonintegrable dynamics leaves clear signatures in the emitted gravitational waves. Nearby regular and chaotic trajectories can remain similar in the time domain and retain broadly aligned dominant spectral peaks, yet chaotic signals develop a much less discrete frequency-domain structure with dense interpeak power. Furthermore, we introduce a local spectral-flatness measure and find it to be several hundred times larger for the chaotic signal than for the neighboring regular signals. Finally, a change in the secondary spin by as little as 1% of its maximal physically allowed value can drive the system from regular to chaotic motion and produce distinctive detector-level waveforms.

We study the loss of hyperbolicity of perturbation equations for black hole solutions of scalar Gauss-Bonnet gravity. We consider a class of coupling functions allowing for static black hole solutions with arbitrary small masses. For masses below a minimum value, such solutions become unphysical, because the perturbation equations become elliptic; this arguably corresponds to the loss of validity of the effective field theory. We analyze the dependence of this minimum mass on the parameters of the theory, finding that with an appropriate choice of the coupling function, such mass can be chosen arbitrarily small. However, this does not correspond to larger deviations from general relativity, since observable quantities like the black hole scalar charge are bounded by above.

We investigate gravity-induced entanglement between the output optical fields of two red-detuned pulsed optomechanical systems with their masses coupled by mutual gravitational interaction. For each individual system, the optomechanical interaction realizes a beam-splitter state swap between an incident optical pulse and its mechanical mode. Using two rectangular pulses for each system—the first to imprint a nonclassical state on the mechanical modes and the second to read the gravitationally generated entanglement back onto the outgoing light—we show that the amount of entanglement can be amplified by preparing the input in a squeezed or Fock state. However, the threshold for entanglement generation is set by the competition between the gravitational coupling and thermal decoherence, $g_G>2{\gamma }_m{N}_{\mathrm{th}}$, and cannot be lowered by any choice of input state. We prove this bound for two-mode Gaussian inputs and show that it continues to hold for Fock-state inputs. We further analyze how imperfect detection modifies the threshold and identify the entanglement-annihilating and entanglement-breaking regimes, which are set by the thermal decoherence accumulated over the interaction time, independent of the gravitational coupling.