The time until black-hole formation in a binary neutron-star (NS) merger contains invaluable information about the nuclear equation of state (EOS) but has thus far been difficult to measure. We propose a new way to constrain the merger remnant’s NS lifetime, which is based on the tendency of the NS-remnant neutrino-driven winds to enrich the ejected material with helium. Based on the He i $\lambda 1083.3\mathrm{nm}$ line, we show that the feature around 800–1200 nm in AT2017gfo at 4.4 days seems inconsistent with a helium mass fraction of $X_{\mathrm{He}}\gtrsim 0.05$ in the polar ejecta. Our recent neutrino-hydrodynamic simulations of merger remnants are only compatible with this limit if the NS remnant collapses within 20–30 ms. Such a short lifetime implies that the total binary mass of GW170817, $M_{\mathrm{tot}}$, lay close to the threshold binary mass for direct gravitational collapse, $M_{\text{thres}}$, for which we estimate $M_{\text{thres}}\lesssim 2.93M_{\odot }$. This upper bound on $M_{\text{thres}}$ yields upper limits on the radii and maximum mass of cold, nonrotating NSs, which rule out simultaneously large values for both quantities. In combination with causality arguments, this result implies a maximum NS mass of $M_{\max }\lesssim 2.3M_{\odot }$. We include an updated constraint yielding lower limits on NS radii from a previous argument that the remnant did not promptly collapse, which is independent of the consideration of the helium content. The combination of all limits constrains the radii of $1.6M_{\odot }$ NSs to about $12\pm 1\mathrm{km}$ for $M_{\max }=2.0M_{\odot }$ and $11.5\pm 1\mathrm{km}$ for $M_{\max }=2.15M_{\odot }$. This $\sim 2\mathrm{km}$ allowable range tightens significantly for $M_{\max }$ above $\approx 2.15M_{\odot }$. This rules out a significant number of current EOS models. The short NS lifetime also implies that a black-hole torus, not a highly magnetized NS, was the central engine powering the relativistic jet of GRB170817A. Our work motivates future developments to further corroborate and improve uncertainties in our chain of arguments regarding non-local-thermodynamic-equilibrium spectral modeling, helium production in merger outflows, and the dependence of the remnant lifetime on the binary mass, with the potential to tighten our constraints from existing data and in particular from future events. This novel method may provide a powerful tool to get a handle on the poorly constrained remnant lifetime, the still debated central engine of short gamma-ray bursts, and the high-density EOS.

The dynamics and instability of the magnetized jets connected to jet acceleration are complicated and are not yet well understood. Quasiperiodic oscillations (QPOs) as special timing features in black hole systems can directly probe dynamics and structure of accreting and outflow materials. Recently, GHz-band radio polarization oscillations in a stellar-mass black hole are reported, and the physical origin is unclear. We propose that the QPOs in both radio flux and linear polarization will be connected to kink instability in relativistic magnetized jets. The simulations are performed to fit the observed curves of radio flux and linear polarization modulations, in addition, the kink instability model well explains the anticorrelation between flux and linear polarization. These polarized QPOs provide evidence for kink stability in relativistic jets, a phenomenon of significant theoretical importance for understanding the magnetic field configuration near the black hole, as well as for particle acceleration in jets.

Multiple models have been suggested over the years to explain the structure and support of accretion disks around supermassive black holes—from the standard thin thermal-pressure-dominated $\alpha$-disk model to more recent models that describe geometrically thicker radiation or magnetic or turbulence-dominated disks. In any case, objects embedded in the disk (e.g. compact objects, stars, gas, dust) can undergo gravitational and hydrodynamic interactions with each other leading to interesting processes such as binary interaction/capture, gravitational wave merger events, dynamical friction, accretion, gap opening, etc. It has long been argued that disks of active galactic nuclei (AGN) can enhance the rates for many of these events; however, almost all of that analysis has assumed specific thin-disk models (with aspect ratios $H/R\lesssim 0.01$). We show here that the rates for processes such as these that are mediated by gravitational cross sections has a very strong inverse dependence on the thickness $H/R$ (scaling as steeply as $(H/R{)}^{-8}$), and $H/R$ can vary in the outer disk (where these processes are often invoked) by factors $\gtrsim 1000$ depending on the assumed source of pressure support in the disk. This predicts rates that can be lower by tens of orders-of-magnitude in some models, demonstrating that it is critical to account for disk parameters such as aspect ratio and different sources of disk pressure when computing any meaningful predictions for these rates. For instance, if magnetic pressure is important in the outer disk, as suggested in recent work, capture rates would be suppressed by factors $\sim {10}^{10}–{10}^{20}$ compared to previous studies where magnetic pressure was ignored.

The ionization of dense molecular clouds offers a powerful and robust probe of dark matter models that produce UV or x-ray photons via annihilation or decay. Using this novel observable, we derive competitive constraints on dark matter in the mass range from 30 eV to 1 keV. In particular, we set the strongest existing limits on axionlike dark matter in the 30–100 eV range. We also present sensitivity projections demonstrating the significant potential of this approach. These constraints can be substantially improved with targeted observations of molecular clouds near the Galactic Center and above the Galactic plane as well as with a more accurate modeling of cosmic-ray ionization and refined gas density estimates from dust extinction maps. Our results establish molecular cloud ionization as one of the most sensitive tools for probing sub-keV dark matter.

Matching theoretical predictions to experimental data remains a central challenge in hadron spectroscopy. In particular, the identification of new hadronic states is difficult, as exotic signals near threshold can arise from a variety of physical mechanisms. A key diagnostic in this context is the pole structure of the scattering amplitude, but different configurations can produce similar signatures. The mapping between pole configurations and line shapes is especially ambiguous near the mass threshold, where analytic control is limited. In this work, we introduce an uncertainty-aware machine learning approach for classifying pole structures in $S$-matrix elements. Our method is based on an ensemble of classifier chains that provide both epistemic and aleatoric uncertainty estimates. We apply a rejection criterion based on predictive uncertainty, achieving a validation accuracy of nearly 95% while discarding only a small fraction of high-uncertainty predictions. Trained on synthetic data with known pole structures, the model generalizes to previously unseen experimental data, including enhancements associated with the $P_{c\overline{c}}(4312{)}^{+}$ state observed by LHCb. In this, we infer a four-pole structure, representing the presence of a genuine compact pentaquark in the presence of a higher channel virtual state pole with nonvanishing width. While evaluated on this particular state, our framework is broadly applicable to other candidate hadronic states and offers a scalable tool for pole structure inference in scattering amplitudes.

Motivated by systematic observations of $B_c$ decays at LHCb, we analyze $B_c^{+}\to J/\psi (A,T)$ decays [where $A$ denotes axial-vector mesons $a_1(1260{)}^{+}$, $b_1(1235{)}^{+}$, and $T$ denotes tensor mesons $a_2(1320{)}^{+}$, $K_2^{*}(1430{)}^{+}$] within the perturbative QCD (pQCD) factorization framework. The framework employs light-cone distribution amplitudes to regulate nonperturbative dynamics, utilizing Sudakov suppression to control endpoint divergences. Our predictions indicate branching ratios of ${10}^{-3}–{10}^{-2}$ for $B_c^{+}\to J/\psi A$ and ${10}^{-5}–{10}^{-4}$ for $B_c^{+}\to J/\psi T$ decays, which seem to be in the reach of future experiments. We also provide predictions for the polarization fractions of these decays. Based on quark helicity analysis, the longitudinal polarization amplitudes are expected to dominate the branching ratios.

As a strong candidate for new physics beyond the Standard Model, the exotic charged gauge boson $W^{\prime }$ has attracted extensive research interest. In this work, we investigate the interactions of the $W^{\prime }$ boson at the electron-proton colliders. The process $e^{-}u\to {\nu }_{e}d$ and $e^{-}u\to e^{\pm }jjj$ with $t$-channel $W^{\prime }$ exchange are studied. The polarization of the initial-state electrons has a significant impact on the cross section of the studied process, while the angular distribution of the final-state leptons serves as an important observable for the interactions of the $W^{\prime }$ boson. In some specific regions of the parameter space, the detectable mass range for the $W^{\prime }$ boson can reach around 10 TeV, and the coupling strength can achieve a precision of approximately 1% relative to the interaction strength of the Standard Model. Especially, $e^{-}u\to e^{+}jjj$ process is forbidden within the Standard Model, which would constitute important evidence in the search for the left-right symmetric model.

We consider an extension to the Standard Model (SM) with four new fields, including scalar($S$), spinor (${\psi }^{1,2}$), and vector($V_{\mu }$), under a new $U(1)$ gauge group in the hidden sector. The scalar particle interacts with the SM Higgs particle and is an intermediary between the dark and the SM parts. Our dark matter (DM) candidate is the spinor particle. We show that the model successfully explains the relic density of the DM in the universe and evades the strong bounds from direct detection experiments while respecting the theoretical constraints and the vacuum stability conditions. In addition, we study the hierarchy problem within the Veltman approach by solving the renormalization group equations at one-loop. We demonstrate that the addition of the new fields contributes to the Veltman parameters, which, in turn, results in satisfying the Veltman conditions much lower than the Planck scale. For our DM model, we find one representative point in the viable parameter space which satisfies also the Veltman conditions at $\mathrm{\Lambda }=1\mathrm{TeV}$. Therefore, the presence of the extra particle solves the fine-tuning problem of the Higgs mass.

We present the first principle calculation of charmed baryon decay constants employing $2+1$ flavor gauge ensembles with lattice spacings ranging from 0.05 to 0.1 fm and pion masses between 136 and 310 MeV. Under SU(3) flavor symmetry, we construct the charmed baryon interpolating operators and compute the corresponding hadronic matrix elements to extract the bare decay constants for each ensemble. The nonperturbative renormalization is performed via the symmetric momentum-subtraction (SMOM) scheme. After performing systematic chiral and continuum extrapolations, we obtain the decay constants with a precision of 8%–16% from first principles. We further determine several ratios of decay constants among different charmed baryons, for which renormalization factors and part of the systematic uncertainties largely cancel, providing a cleaner probe of SU(3) flavor symmetry breaking. These ratios offer a quantitative, first-principles characterization of the SU(3)-breaking pattern in the charmed baryon sector.

We present a systematic decomposition of QCD splitting functions into scalar dipole radiators and pure splitting remainders up to second order in the strong coupling. The individual components contain terms that are formally subleading in soft or collinear scaling parameters, but well understood and universal due to their origin in scalar QCD. The multipole radiator functions which we derive share essential features of the known double-soft and one-loop soft gluon currents, and are not based on kinematical approximations.

In this paper, we employ chiral effective field theory to study the process of electron-positron annihilation into four pions in the low energy region within $E_{\mathrm{c}.\mathrm{m}.}\le 0.6\mathrm{GeV}$. The prediction of the cross section is obtained through $SU(3)$ chiral perturbation theory up to the next-to-leading order, which is smaller than the experimental data in the energy region [0.6–0.65] GeV, though the data has only a few points and poor statistics. Then, the resonance chiral theory is applied to include the resonance contribution, with the lightest scalars and vectors written in the effective Lagrangians. A series of relevant decay widths and the masses of the vectors are studied to fix the unknown couplings. The resonance contribution should be one order larger than that of the chiral perturbation theory but still one to two orders smaller than the data. The significant discrepancy urged the new experimental measurements to give more guidance. We also compute the leading order hadronic vacuum polarization contribution from the four pion channels to the anomalous magnetic moment of the muon, $(g-2{)}_{\mu }$. In the energy range from threshold up to 0.6 GeV within resonance chiral theory, the contributions are $a_{\mu }=(0.680\pm 0.062)\times {10}^{-16}$ and $a_{\mu }=(0.597\pm 0.058)\times {10}^{-16}$ for the processes of $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^{-}$, ${\pi }^0{\pi }^0{\pi }^{+}{\pi }^{-}$, respectively.

In light of recent precision measurements from BESIII, we reanalyze the $D,D_s\to {\eta }^{(\prime )}$ transition form factors using quantum chromodynamics (QCD) light-cone sum rules, incorporating high-twist contributions and well-established next-to-leading-order QCD corrections. Our analysis confirms the chiral enhancement effect arising from twist-3 light-cone distribution amplitudes of the pseudoscalar mesons, and demonstrates a rapid convergence of the operator product expansion. The resulting high-accuracy form factors enable us to determine the optimal $\eta -{\eta }^{\prime }$ mixing parameters from the precise experimental data for the $D,D_s\to {\eta }^{(\prime )}{\ell }^{+}{\nu }_{\ell }$ (with $\ell =e$, $\mu$) differential decay rates. We find that the BESIII data strongly favor a set of mixing parameters, characterized by small decay constants and a large mixing angle, in the quark flavor basis. Notably, the light-cone-sum-rule predictions for the decays $D\to {\eta }^{(\prime )}{\ell }^{+}{\nu }_{\ell }$, induced by weak $c\to d$ current, reach a precision comparable to the BESIII experimental results. Nevertheless, further refined measurements and more accurate form-factor determinations will be essential to scrutinize the potential role of gluonic components in charmed meson semileptonic decays.

We develop and implement a new hybrid waveform model for quasicircular inspirals with a spinning primary and nonspinning secondary, excluding the merger and ringdown. This model, which is a core component of the more extensive WaSABI-C model, consistently assembles all available first-order self-force and post-Newtonian results through a hybridization procedure without any tuning to numerical relativity, making it particularly suited for intermediate to extreme mass ratios. For almost all masses and primary spins, the resulting hybrid model significantly improves the faithfulness of both post-Newtonian and adiabatic self-force waveforms considered separately. We provide detailed comparisons with 50 simulations from the SXS catalog with mass ratios ranging from 1 to 15 and primary spins ranging from $-0.8$ to 0.8. The hybrid model improves the median mismatch against numerical relativity waveforms by a factor of 2000 with respect to adiabatic waveforms and 40 with respect to post-Newtonian waveforms. The mismatches are comparable to those obtained from the SEOBNRv5EHM model in the quasicircular limit over most of the parameter space covered by numerical relativity simulations.

Recent progress in gravitational self-force theory has led to the development of a first postadiabatic (1PA) waveform model for nonspinning, quasicircular compact binaries [Phys. Rev. Lett. 130, 241402 (2023)]. In this paper, we extend that model to allow for a slowly spinning primary black hole and a generic, precessing spin on the secondary object, restricting to the case of small misalignment between the primary spin and the orbital angular momentum. We demonstrate excellent agreement between our waveforms and fully nonlinear numerical relativity simulations for mass ratios $q\gtrsim 5$ and primary spins $|{\chi }_1|\lesssim 0.1$ and arbitrary secondary spin ${\chi }_2\lesssim 1$. In particular we present the resummed 1PAT1R waveform model, which significantly improves the accuracy of the original 1PAT1 waveforms for comparable masses and increasing primary spin. Our models are publicly available in the wasabi package.

In the coming decades, as the low-frequency sensitivity of detectors improves, the time that gravitational-wave signals remain in the sensitive band will increase, leading to new challenges in analyzing data, namely nonstationary noise and data gaps. Time-frequency (wavelet) methods can efficiently handle nonstationary noise, but data gaps still lead to spectral leakage due to the finite length of the wavelet filters. It was previously shown that Bayesian data augmentation—“gap filling”—could mitigate spectral leakage in frequency domain analyses, but the computational cost associated with the matrix operations needed in that approach is prohibitive. Here we present a new, computationally efficient approach to Bayesian data augmentation in the time-frequency domain that avoids repeated, costly matrix operations. We show that our approach efficiently solves the problem of data gaps in simulated Laser Interferometer Space Antenna (LISA) data and can be smoothly integrated into the LISA Global Fit. The same approach can also be used for future third-generation ground-based interferometers.

We present a fully Bayesian framework for time delay inference and stationarity tests in quasar light curves using marginalized Gaussian processes. The model separates a deterministic, nonstationary drift (piecewise linear mean) from stationary stochastic variability (Matérn and Spectral Mixture kernels), and jointly models multiple images with per-image microlensing. Bayesian evidence and parameter posteriors are obtained via nested sampling and marginalized over model choices. Applied to the quasars WFI J2033–4723, B $1608+656$, and HE 0435–1223, we find strong evidence for nonstationarity in B $1608+656$ and HE 0435–1223, while WFI J2033–4723 is consistent with stationarity. The stochastic component favors an Markovian exponential kernel for B $1608+656$ and a non-Markovian Matérn-$\frac{3}{2}$ kernel for WFI J2033–4723 and HE 0435–1223. Multilength-scale Spectral Mixture kernels are disfavored. Time delays are shown to be robust to model assumptions and consistent with prior work within the error. We further identify and mitigate a likelihood pathology which biases toward large delays, providing a practical nested sampling convergence protocol.

Ultralight dark matter may couple quadratically to Standard Model particles. Such quadratic interactions give rise to both coherent and stochastic signals in pulsar timing array (PTA) observations. In this work, we characterize these signals, including the effects of dark matter propagation in a finite-density medium, and assess the sensitivity of current and upcoming PTA observations to their detection. For coherent signals, we find that the sensitivity of current PTA observations competes with and sometimes exceeds that of other probes, such as equivalence principle tests and atomic clocks. For stochastic signals, we find that PTA sensitivities underperform equivalence principle constraints for both existing and upcoming PTA datasets.

We study the influence of positrons on the outer crusts of neutron stars and the interiors of white dwarfs, introducing them as a novel component in both the composition of matter and in transport processes. We solve a system of coupled Boltzmann kinetic equations for the electron and positron distribution functions in the relaxation-time approximation, taking into account electron-ion, positron-ion, and electron-positron collisions. The relevant scattering matrix elements are calculated from one-plasmon exchange diagrams, with in-medium polarization tensors derived within the hard-thermal-loop effective theory. Numerical results are obtained for matter composed of carbon, iron, and helium nuclei. We find that the conductivity rises with temperature, following a power law $\sigma \propto T^4$ in the semidegenerate regime and $\sigma \propto T$ in the nondegenerate regime, due to the intense creation of thermal electron-positron pairs and the resulting collisions among them. These results highlight the importance of including positrons in the transport properties of heated, dense astrophysical plasmas.

We present a systematic calculation of the axial charges and magnetic moments for the decuplet of hidden-charm molecular pentaquarks within the framework of the constituent quark model. Our findings reveal that the axial charges of these states are comparable in magnitude to that of the nucleon. Furthermore, we find that their magnetic moments obey a set of sum rules which hold for states sharing the same spin-flavor configuration, even in the presence of SU(3) flavor symmetry breaking. These results provide crucial insights into the internal structure and dynamics of multiquark hadrons, offering valuable guidance for future experimental and theoretical investigations, ${\mu }_{P_{\psi }^{\mathrm{\Delta }+}}-{\mu }_{P_{\psi }^{\mathrm{\Delta }0}}+{\mu }_{P_{\psi s}^{\mathrm{\Sigma }-}}-{\mu }_{P_{\psi s}^{\mathrm{\Sigma }+}}+{\mu }_{P_{\psi ss}^{N0}}-{\mu }_{P_{\psi ss}^{N-}}=0,{\mu }_{P_{\psi }^{\mathrm{\Delta }++}}+{\mu }_{P_{\psi }^{\mathrm{\Delta }-}}+{\mu }_{P_{\psi sss}^{\mathrm{\Lambda }-}}=3{\mu }_{P_{\psi s}^{\mathrm{\Sigma }0}}$.