We reformulate the stellar structure equations in the language of dynamical systems and show that the maximum mass of stellar sequences arises from the existence of a fixed point in the relativistic regime. In an appropriate representation of the Tolman-Oppenheimer-Volkoff equations, this fixed point becomes manifest and is directly associated with the turnover of the mass-radius curve. The existence of a fixed point implies an effective reduction in dimensionality near the onset of instability, which provides a simple explanation for several equation of state–insensitive relations and predicts new ones. In the weakly relativistic limit, we identify a complementary universal structure shared by stellar sequences at their maximum mass, which we term the “compressible limit,” and derive distinct universal relations governing the maximum mass in the Newtonian and post-Newtonian regimes. Combining these theoretical results with current astrophysical constraints, we show that the $\mathrm{J}0740+6620$ pulsar is unlikely to lie near the Tolman-Oppenheimer-Volkoff maximum mass unless the equation of state exhibits a strong first-order phase transition at densities just above its central density.

Black holes with resonant hair are static, spherical, electrically charged solutions of the Einstein-Maxwell-(gauged-)scalar system. Scalar self-interactions are mandatory for their existence. Initial dynamical studies restricted to spherical symmetry suggested stability; more recently, fully nonspherical dynamical studies revealed instabilities, at least for a particular class of self-interactions. Here, we provide a more detailed study of this instability together with a different decay channel, depending on the chosen solutions. Moreover, considering a second model, we provide evidence that the instabilities may be generic for different classes of self-interactions. We conclude these solutions are dynamically unstable and split into a bosonic lump and a bald black hole (via fission) or implode to the latter (via absorption). In both cases, the nonspherical dynamics seems to be key.

In previous works, matter trapping surfaces (MTS) were defined as hypersurfaces separating cosmologically expanding regions of spacetime from regions where collapse can take place independently. In the present work we examine the MTS, for the restriction to spherical dust plus $\mathrm{\Lambda }$, proving that it actually is a characteristic surface of the Cauchy problem (generated by its characteristic curves), which opens the possibility for infinite solutions. This translate as the MTS being a boundary between arbitrarily independent solutions, reminiscent of the Birkhoff theorem effects. This property is illustrated with combinations of three examples containing MTSs and $\mathrm{\Lambda }$ ($\mathrm{\Lambda }\mathrm{CDM}$, Schwarzschild–de Sitter, $\mathrm{\Lambda }+$Lemaître–Tolman–Bondi: $\mathrm{\Lambda }\mathrm{LTB}$—i.e., the inhomogeneous, spherically symmetric $\mathrm{\Lambda }\mathrm{CDM}$). The $\mathrm{\Lambda }\mathrm{LTB}$ model presents a static, stable MTS for the first time.

Spectral-siren cosmology constrains the Hubble constant $H_0$ using gravitational-wave observations of compact-binary coalescences. The method combines luminosity distances inferred from the waveform with redshift information statistically encoded in population features of the source-frame mass spectrum. Because the detector measures redshifted masses, structure in the intrinsic mass distribution acts as an internal “ruler,” making the inference sensitive to assumptions about the population model. In particular, redshift evolution of the mass spectrum is widely discussed as a potential systematic for $H_0$ measurements. We revisit spectral-siren constraints with the GWTC-4.0 binary black hole catalog, explicitly allowing the main mass scales of a standard parametric mass model to evolve with redshift. We find no compelling evidence for evolution at current sensitivity. Allowing evolution produces a modest, nonstatistically significant shift of the $H_0$ posterior toward lower values, which we interpret with targeted posterior and event-level diagnostics. Importantly, the associated systematic uncertainty is subdominant to that induced by alternative redshift-independent descriptions of the mass spectrum, such as the number of spectral features and the functional form used to model them. Our results indicate that, at current sensitivity, spectral-siren constraints on $H_0$ are robust to redshift evolution of the mass spectrum within the flexibility explored here. Using injection studies, we show that this mild $H_0$ shift is reproduced when a nonevolving underlying population is analyzed with an evolving model, consistent with an overflexible population description at the present signal-to-noise. The sign and magnitude of the shift can, however, depend on detector sensitivity and redshift reach as the population features become increasingly constrained directly by the data, motivating targeted diagnostics for future catalogs.

The Laser Interferometer Space Antenna is expected to observe gravitational waves from massive black hole binaries across cosmic time. Many are anticipated to be detectable hours to weeks before coalescence. We present a fast algorithm for the premerger detection and preliminary characterization of such binaries. The method performs a search for excess power with a chirping time-frequency morphology in short-time Fourier transform spectrograms. By tiling the time-frequency plane with slices defined by the quadrupole frequency evolution, we define a signal significance relative to a fitted background distribution of instrumental noise and Galactic foreground. Individual search triggers are followed by a coherence tracker that groups triggers consistent with the same physical signal over time. Doing so, our analysis provides progressively refined estimates of the chirp mass and coalescence time. We validate our algorithm on the SangriaHM LISA Data Challenge dataset, successfully detecting all 15 injected massive black hole binaries; 14 of them hours to weeks before merger, while one is only detected after the binary coalescence. The algorithm yields chirp mass relative errors below 3% for high-SNR sources and coalescence time uncertainties of up to a few hours. With a computational cost of less than a second to process a 10-day data segment on a single core, our approach is suitable for generating real-time alerts, triggering protected observational periods, and providing informative priors for Bayesian parameter estimation.

We present the results of directed searches for continuous gravitational waves from unknown neutron stars in five Milky Way globular clusters. We carry out these searches in the LIGO data from the first eight months of the fourth LIGO-Virgo-KAGRA observing run using the weave semicoherent program, which sums matched-filter detection-statistic values over many time segments spanning the observation period. No gravitational wave signal is detected in the search band of 20–475 Hz. Injections of simulated continuous wave signals in the data indicate that we achieve the most sensitive results to date across most of the explored parameter space volume, obtaining median 95% confidence level upper limits as low as $\sim 4.2\times {10}^{-26}$ near 282 Hz for NGC 6397. We also derive upper limits on neutron star ellipticity and $r$-mode amplitudes, reaching $\lesssim {10}^{-5}$ and $\lesssim {10}^{-3}$, respectively, at frequencies above 200 Hz.

Mellin-Barnes (MB) integrals appear in various branches of physics and mathematics and are, in particular, used as a standard tool for evaluating multiloop, multiscale Feynman integrals both analytically and numerically. Recent geometric approaches based on conic hulls and triangulations provide a systematic framework for computing multiple MB integrals in terms of multivariate series. These approaches have so far been limited to MB integrals whose integrands are ratios of products of Euler’s gamma functions only. However, in Feynman integral calculus, MB integrals with polygamma functions naturally arise, for instance, after resolving singularities in the dimensional-regularization parameter $\epsilon$ and expanding the MB integrand in powers of $\epsilon$, as done by the public codes mb.m and mbresolve.m. In this paper, we extend the conic hull and triangulation methods to the computation of MB integrals having polygamma functions in their integrand. We show that the arguments of polygamma functions can be treated in a similar way to the arguments of gamma functions when applying the conic hull and triangulation techniques to identify poles that would contribute to different series solutions. However, since the singularity structure of the polygamma function is different from that of the gamma function, we propose two different ways to compute MB integrals involving polygamma functions, depending on whether the MB integral has straight or nonstraight contours. We have implemented these algorithms in an updated version of the Mathematica package mbconichulls.wl, and we illustrate their use with a set of examples from Feynman integral calculus.

We provide a complete first-principles based discussion of quantum tunneling out of initial states carrying a conserved Noether charge. Our main result is a simple, unambiguous Euclidean-time prescription for the calculation of tunneling rates out of such states. By relying on a combination of the direct approach and the steadyon framework for the evaluation of real-time path integrals, our derivation offers full transparency of its underlying assumptions, and is independent of any ad hoc generalizations. This strategy also offers a simple explanation for the emergence of complex saddle points for such systems, justifying techniques postulated by earlier works. Our analysis furthermore offers the first results for initial states with both a conserved Noether charge and a nontrivial energy. We first illustrate the main conceptual points of our analysis for the simple example of a point particle in two spatial dimensions carrying a conserved angular momentum. Then, we generalize our results to the case of multiple dimensions and an arbitrary conserved Noether charge, providing an easy-to-implement prescription for the calculation of the tunneling rate. We furthermore apply our results to the example of a complex scalar field subject to a global $U(1)$-symmetry with associated charge. These results provide a reliable foundation for the calculation of tunneling rates in applications in finite-density and charge-asymmetric systems.

We investigate thermal photon emission from magnetized quark-gluon plasma (QGP) within ($1+1$)-dimensional relativistic magnetohydrodynamics (MHD), systematically incorporating magnetic susceptibility ${\chi }_m$—encompassing both constant and lattice-QCD-derived temperature-dependent ${\chi }_m(T)$ parametrizations—and weak-field quantum corrections to quark distribution functions $f_{\mathrm{EM}}$. Employing the Pu-Bjorken MHD framework, we calculate photon production rates from Compton scattering, $q\overline{q}$ annihilation, bremsstrahlung, and annihilation with rescattering, and integrate these over the QGP spacetime evolution to obtain transverse momentum ($p_T$) spectra. Our results demonstrate that photon yields are predominantly governed by the initial magnetic field strength and its temporal decay profile, with ${\chi }_m$ exerting negligible influence in the explored parameter space. In contrast, the weak-field correction $f_{\mathrm{EM}}$ induces a distinct enhancement in thermal photon production at intermediate $p_T$. This work establishes a rigorous theoretical framework for quantifying electromagnetic observables in magnetized QGP and provides the foundation for future dissipative MHD studies incorporating spin-magnetization dynamics.

We explore the sensitivity of the Sudbury Neutrino Observatory (SNO) experiment to light dark matter particles $\chi$ with spin-dependent interactions with nucleons. We show that the pair-production of MeV scale dark matter is possible in heavy water (CANDU (Canada Deuterium Uranium)) reactors via $\mathrm{D}(n,\chi \overline{\chi }){}^3\mathrm{He}$, and calculate the expected rate within the simplest models of $\chi$-nucleon interactions. Owing to a sizable $Q$-value for this reaction, a large fraction of dark matter (DM) particles produced this way are above the threshold for deuteron disintegration, $\mathrm{D}(\chi ,\chi )np$, which adds to the SNO neutral current signal. Evaluating the CANDU-to-SNO scheme for the production and detection of DM, we derive novel constraints for the $\chi$-nucleon spin-dependent cross sections, showing that cross sections above ${\sigma }_{\chi p}\sim {10}^{-33}{\mathrm{cm}}^2$ are generally excluded if $m_{\chi }\le 1.5\mathrm{MeV}$. An isospin-mirror reaction will occur in the Sun, and for the kinematically allowed region it excludes a portion of parameter space with cross sections on the order ${10}^{-37}{\mathrm{cm}}^2$. We also evaluate the potential sensitivity of small “near” detectors placed in close proximity to a CANDU reactor to search for a coherent nuclear recoil, finding subdominant sensitivity.

A formalism for radiative correction calculations in exclusive $\eta$ electroproduction on the proton is presented, extending the treatment developed for the pion channel. The exclurad code is used in the radiative correction procedure with EtaMAID-2023 multipole amplitudes. The cross-section correction factor $\delta$ varies by up to $\sim 30\%$ across the resonance region $W=1.49–2.0\mathrm{GeV}$ at $E_{\mathrm{beam}}=6.535\mathrm{GeV}$, with a local maximum near $W\simeq 1.66\mathrm{GeV}$ driven by the $S_{11}(1535)$ and $S_{11}(1650)$ resonances. The beam-spin asymmetry is suppressed by 15%–25% at the same kinematics. Numerical results covering $Q^2=0.3–4.0{\mathrm{GeV}}^2$ and the full angular range are provided for kinematics relevant to CLAS12 experiments at Jefferson Lab.

We perform a new global QCD analysis of unpolarized parton distribution functions (PDFs) in the nucleon from proton, deuteron, and $A=3$ data, including recent measurements of ${}^3\mathrm{He}/D$ and ${}^3\mathrm{H}/D$ cross section ratios from the MARATHON experiment at Jefferson Lab. Simultaneously inferring the PDFs and nucleon off-shell corrections allows both to be determined consistently, without theoretical assumptions about the isospin dependence of nuclear effects. The analysis provides strong evidence for the need of nucleon off-shell corrections to describe the $A=3$ data, with large isoscalar and a suggestion of nonzero isovector contributions in $A\le 3$ nuclei. We find that the extracted EMC ratios of nuclear to nucleon structure functions for $A=2$ and 3 differ from those naively extrapolated from heavy nuclei down to low $A$.

Corrections to vacuum black hole solutions of general relativity (GR) are considered in an effective field theory (EFT) framework, perturbatively in EFT coefficients, focusing on the Schwarzschild solution of GR. We find dominant corrections to the Schwarzschild metric in all orders in the derivative expansion far away from the horizon. These corrections can be summed up in a closed form through EFT coefficients up to all orders in derivatives and to the second order in curvature. It occurs that such a summation is convergent only for localizable theories, making a direct connection between the graviton scattering amplitudes properties and the applicability of a perturbative treatment of an EFT of gravity. We further apply our results to logarithmic form factors which appear in the one-loop effective action for GR in four dimensions. We find out that the corresponding corrections to the Schwarzschild metric are stronger than those from the tree-level EFT operators. The developed framework can be extended to account for the corrections to the other black hole solutions in GR, such as the Kerr metric.

We present a complementary approach to the standard Vasiliev framework for nonlinear higher-spin interactions in four dimensions, aimed at identifying their minimally nonlocal form. Our proposal introduces a generating system for higher-spin vertices at the level of classical equations, which we refer to as irregular, in contrast to the regular case described by Vasiliev. This system extends the recently proposed equations for (anti)holomorphic interactions by incorporating the mixed sector. Its perturbative series encompasses the entire (anti)holomorphic sector in the leading order, with vertices related to powers of the complex parity-breaking parameter $\eta$ or $\overline{\eta }$. The subsequent corrections facilitate the mixing of the two sectors, with vertices carrying mixed powers of $\eta$ and $\overline{\eta }$. Consistency relies on the nonlinear algebraic constraint, which is shown to be satisfied, at least, in the quadratic and cubic approximations. As a result, the previously discussed (anti)holomorphic interactions in the literature can be systematically extended to generate vertices of the form ${\eta }^N{\overline{\eta }}^k$ and their conjugate, at least for $k\le 2$ and any $N$. As a byproduct of our analysis, we also identify the new higher-spin structure dualities.

We investigate the dynamics of asymmetric binaries in extensions of general relativity (GR) featuring a massless scalar field nonminimally coupled to gravity, focusing on the interplay between eccentricity and inclination in fully generic bound orbits. Building on an effective field theory framework tailored to extreme- and intermediate-mass-ratio inspirals, we compute scalar-field perturbations using a new arbitrary-precision c++ code capable of evolving perturbations along generic Kerr geodesics, storm. We investigate the complete set of scalar fluxes at infinity and through the horizon across the relevant parameter space and analyze their harmonic structure as a function of orbital geometry and black-hole spin. Our results advance ongoing efforts to construct accurate waveform models for asymmetric binaries beyond GR and lay the groundwork for precision tests of fundamental physics with next-generation gravitational-wave detectors.

We study the plunge and merger of a nonspinning particle falling into a Kerr black hole following an eccentric planar inspiral. The dynamics is driven by an effective-one-body radiation reaction and the corresponding numerical inspiral-merger-ringdown waveforms are obtained by solving the Teukolsky equation with the $2+1$ time-domain code teukode. We then analyze in detail the plunge and merger phases, modeling the merger-ringdown waveform using closed-form Ansätze. Crucially, our modeling starts from a point closely related to the light-ring crossing, rather than from the amplitude peaks. This choice allows us to neglect the impact of the relativistic anomaly at the separatrix crossing and to extend the modeling to high spins and high eccentricities. We model all the multipoles with $m\ge 1$ up to $\ell =4$, as well as the (2, 0), (5, 5), (5, 4), and (5, 3) modes, including spherical-spheroidal mode mixing and the beating between corotating and counterrotating quasinormal modes. The postmerger waveform model is then employed to complete an effective-one-body inspiral-plunge waveform, thus providing a complete description. Our model, built using ellipticlike configurations for the merger-ringdown phase, naturally extends to dynamical capture scenarios without any further modification. Finally, we provide insights into the extension of this framework to generic mass ratios, arguing that a time closely related to the inflection point of the (2, 2) waveform frequency could be used as anchoring point for the ringdown modeling.

We study the scalar and Dirac perturbations of quantum-corrected black holes with cosmological constant. Using two different methods (WKB and double-null characteristic integration) we compute the quasinormal modes (QNMs) of de Sitter and anti–de Sitter solutions considering linear field perturbations in the background geometry. In the limit of general relativity black holes, our methods demonstrate good convergence with the available results in literature. In the presence of an extra quantum parameter, we verify that all perturbations are stable evolving in towers of quasinormal oscillations. We scrutinize the spectra of both dS and AdS solutions studying the influence of that extra parameter in the frequencies.

We present realistic forecasts for the constraining power of the Nancy Grace Roman Space Telescope on fundamental cosmological parameters, with particular emphasis on the absolute neutrino mass scale, using full-shape analyses of the galaxy power spectrum. We analyze simulated light cone mock catalogs of $\mathrm{H}\alpha$ emission-line galaxies spanning the redshift range $0.5<z<2$ over $2400{\mathrm{deg}}^2$, designed to reproduce the expected properties of the Roman High Latitude Wide Area Spectroscopic Survey. We perform parameter inference on the galaxy power spectrum multipoles using two complementary theoretical frameworks: a model-dependent approach based on the effective field theory of large-scale structure (EFT of LSS) within $\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$), and a model-independent phenomenological approach that makes no assumptions about the background cosmological model. In the $\mathrm{\Lambda }\mathrm{CDM}$ analysis, we find $m_{\nu }<0.380(0.162)\mathrm{eV}$ at 95(68)% CL using big bang nucleosynthesis (BBN) prior and a broad prior on $n_s$, which tightens to $m_{\nu }<0.276(0.121)\mathrm{eV}$ when Planck priors on ${\omega }_b$, ${\omega }_{\mathrm{cdm}}$, and $n_s$ are added. Our forecasts show that Roman can additionally constrain $H_0$, ${\mathrm{\Omega }}_m$, and ${\sigma }_8$ with precisions of 1.3%, 4.3%, and 2.9% in line with stage IV galaxy survey measurements and forecasts. In the model-independent analysis, we demonstrate that the phenomenological model can robustly recover unbiased measurements of the angular diameter distance, the Hubble parameter, and the growth of structure across all redshift bins, in the same range of scales as the EFT model, and obtain $m_{\nu }<0.63(0.36)\mathrm{eV}$ at 95(68)% CL when Planck priors are included.

There is mounting evidence from multiple cosmological probes that dark energy may be dynamical, with an equation of state that evolves over cosmic time. While this evidence is typically quantified using the Chevallier-Polarski-Linder (CPL) parametrization, based on a linear expansion of $w(a)$ in the scale factor, nonparametric reconstructions frequently suggest nonlinear features, particularly at late times. In this work, we investigate four minimal one-parameter models of dark energy with nonlinear dependence on the scale factor. These models are constrained using cosmic microwave background data from Planck, lensing reconstruction from Planck and ACT-DR6, baryon acoustic oscillation measurements from DESI-DR2, and three type Ia supernovae (SNe) samples (PantheonPlus, DESY5, and Union3), considered independently. Although our conclusions depend on the choice of SNe sample, we consistently find a preference, as measured by the chi-squared statistic and the Bayesian evidence, for these dynamical dark energy models over the standard $\mathrm{\Lambda }\mathrm{CDM}$ (cold dark matter) model. Notably, with the PantheonPlus dataset, one model shows strong Bayesian evidence ($\mathrm{\Delta }\ln B\simeq 4.5$) over CPL, favoring an equation of state that peaks near $a\simeq 0.7$ and oscillates near the present day. These results highlight the impact of SNe selection and contribute to the growing collection of evidence for late-time deviations from $\mathrm{\Lambda }\mathrm{CDM}$.

We investigate quantum entanglement and Bell-inequality violation in top-antitop pair production at future lepton colliders such as the International Linear Collider and multi-TeV muon colliders. Within the Standard Model (SM), the process proceeds through $s$-channel $\gamma$ and $Z$ exchange and exhibits characteristic spin-correlation patterns that encode a nontrivial amount of entanglement. We then examine how these features are modified in several well-motivated extensions of the SM; (i) a neutral scalar mediator that couples to charged leptons and top quarks via Yukawa interactions and contributes as an additional $s$-channel exchange, (ii) the minimal gauged $U(1{)}_{B-L}$ model, which introduces a new neutral gauge boson $Z^{\prime }$ coupling vectorially to SM fermions, and (iii) a Randall-Sundrum scenario, in which the exchange of massive Kaluza-Klein gravitons arising from a warped extra dimension induces additional spin-dependent interactions. For all cases, we evaluate quantum-information observables including the entanglement marker, the concurrence, and the maximal Clauser-Horne-Shimony-Holt parameter, and study their dependence on the center-of-mass energy, scattering angle, and model parameters. We find that, relative to the SM expectation, the entanglement is typically reduced in the scalar-mediator scenario, while sizable deviations can arise in the $U(1{)}_{B-L}$ and Randall-Sundrum cases for phenomenologically relevant regions of parameter space. These results demonstrate the potential of quantum-information observables as sensitive probes of new particles and their interaction patterns in future lepton colliders.