The leading-order low-energy constant ${\mathrm{\Delta }}_{\mathrm{mix}}$ in mixed-action chiral perturbation theory is calculated using $2+1+1$-flavor gauge ensembles with HISQ fermions and a tadpole-improved Symanzik gauge action at four lattice spacings $a\in [0.048,0.111]\mathrm{fm}$. By comparing our results to those from different actions and a $2+1$-flavor case, We find that the fermion action has the dominant impact, the gauge action has a secondary but measurable effect, and the contribution from charm quark loops is negligible within our current uncertainties.

Ground-state energy and matrix elements are reconstructed from correlators in lattice QCD by diagonalizing transfer matrix $\widehat{\mathcal{T}}$ within the Krylov subspace spanned by ${\widehat{\mathcal{T}}}^n|\chi ⟩$, where $|\chi ⟩$ is a state generated by an interpolating field on the lattice. In numerical applications, this strategy is spoiled by statistical noise. To circumvent the problem, we introduce a low-rank approximation based on a singular-value decomposition of a matrix made of the correlators. The associated bias is eliminated by an extrapolation to the limit of vanishing variance of energy eigenvalues. The strategy is tested using a set of mock data as well as real data of $K$ and $D_s$ meson correlators.

We scrutinize neutrino magnetic dipole portals of sterile neutrinos in the mass range of 0.1–50 MeV through the nuclear and electron recoils at neutrino scattering experiments. For the $e$-flavor dipole portal, we show that Dresden-II can provide leading constraints for $m_N\lesssim 0.5\mathrm{MeV}$, setting aside unresolved theoretical uncertainties. For the $\mu$-flavor case, we employ a two-dimensional fitting method which could utilize the timing structure measurement of the full dataset collected by the CsI[Na] scintillation detector. With such, we demonstrate that the COHERENT experiment can probe a wide unique parameter region for $m_N$ in the range of 10–40 MeV. Exclusion regions for $\tau$-flavor dipole portal based on latest measurements of the solar neutrino from dark matter direct detection experiments are also presented.

Accurate measurement of the cosmogenic muon-induced neutron yield is crucial for constraining a significant background in a wide range of low-energy physics searches. Although previous underground experiments have measured this yield across various cosmogenic muon energies, $\mathrm{SNO}+$ is uniquely positioned due to its exposure to one of the highest average cosmogenic muon energies at 364 GeV. Using ultrapure water, we have determined a neutron yield of $Y_n=(3.38_{-0.30}^{+0.23})\times {10}^{-4}{\mathrm{cm}}^2{\mathrm{g}}^{-1}{\mu }^{-1}$ at $\mathrm{SNO}+$. Comparison with simulations demonstrates clear agreement with the fluka neutron production model, highlighting discrepancies with the widely used geant4 model. Furthermore, this measurement reveals a lower cosmogenic neutron yield than that observed by the SNO experiment, which used heavy water under identical muon flux conditions. This result provides new evidence that nuclear structure and target material composition significantly influence neutron production by cosmogenic muons, offering fresh insight with important implications for the design and background modeling of future underground experiments.

Black holes (BHs) with synchronized bosonic hair challenge the Kerr paradigm, linking superradiance from ultralight fields—creating gravitational atoms—to bosonic stars across parameter space. In the “very hairy” regime, where a small horizon lies inside a bosonic star containing most of the energy, they deviate sharply from Kerr, but their dynamics remain unexplored. We show that for such solutions the horizon gets naturally ejected from the center of its scalar environment and observe a similar dynamics in a cousin model of BHs with resonant scalar hair, albeit with a different fate. This dynamical splitting is likely to be generic for sufficiently hairy BHs in the broader class of models with synchronized or resonant hair, but possible exceptions may exist.

The recently proposed swampland cobordism conjecture predicts the existence of new nonsupersymmetric objects which supplement the spectrum of low-energy gravitational effective field theories. In this paper, we study a subset of these defects related to the Gliozzi-Scherk-Olive projection on the string worldsheet. These include the predicted domain wall between type IIA and IIB superstring theories and the newly discovered R7-brane. We study these defects in two different ways: via long-string probes and target-space effective field theory. We find that the R7-brane can be identified with a collapsed cylindrical configuration of the IIA/IIB wall, and further, that the R7-brane is stable, in contrast to previous expectations. Moreover, we argue that BPS D-branes pulled across the IIA/IIB wall become non-BPS D-branes, which we identify with fluxbrane configurations. We show that the non-BPS D-branes of either type II theory are charged under a ${\mathbb{Z}}_2$ remnant of the Ramond-Ramond potentials of the other, which we identify with the mod 2 reduction of the Ramond-Ramond fluxes. Similar considerations provide a complementary perspective on the heterotic $\mathfrak{so}(32)$ S-duals of known non-BPS 7- and 8-branes in type I string theory.

Multi-invariants are local-unitary invariants of state replicas introduced as potential probes of multipartite entanglement and correlations in quantum many-body systems. In this paper, we investigate two multi-invariants for tripartite pure states, namely multientropy and dihedral invariant. We compute the (genuine) multientropy for Lifshitz ground states and obtain its analytical continuation to noninteger values of Rényi index. We show that the genuine multientropy can be expressed in terms of mutual information and logarithmic negativity, a relation that also holds for stabilizer states. For general tripartite pure states, we demonstrate that dihedral invariants are related to Rényi reflected entropies. In particular, we show that the dihedral permutations of replicas are equivalent to the reflected construction, or alternatively to the realignment of density matrices.

It was recently shown that, in a binary coalescence, the greybody factor of the remnant black hole modulates the postmerger ringdown signal. In this work, we demonstrate that a simple four-parameter model based on the greybody factor accurately reproduces the frequency-domain amplitude of a large set of comparable-mass, aligned-spin numerical relativity waveforms from the SXS catalog, achieving mismatches of order $\mathcal{O}({10}^{-5})$ and improving existing models by roughly 2 orders of magnitude. We also identify the optimal initial frequency for applying the model in the frequency domain and provide analytical fits of the model parameters in terms of the progenitor masses and aligned spins. Our results pave the way for new consistency tests of the ringdown phase, complementary to traditional black hole spectroscopy.

Rotating hairy black holes (RHBHs) are axisymmetric equilibrium solutions of the Einstein-Klein-Gordon equations, consisting of a spinning black hole surrounded by a toroidal distribution of complex scalar field. Despite their potential astrophysical relevance, the stability of these configurations—naturally expected to form through superradiant growth of light bosonic fields—remains uncertain. In this work, we investigate the stability of RHBHs by performing fully nonlinear numerical evolutions of several configurations that differ in the relative mass contribution of the scalar-field torus. We find that configurations in which the scalar-field mass is subdominant compared to the black hole mass remain stable throughout the evolution, at least on timescales of order $\mu t>1600$, where $\mu$ is the scalar-field mass. These configurations might therefore be stable, with possible superradiant instabilities developing only on much longer timescales $\mu t\sim {10}^{11}$, according to previous linear stability analyses. In contrast, when the scalar-field mass dominates, the system develops an instability in a much shorter timescale around $\mu t\sim \mathcal{O}(100)$, similar to the nonaxisymmetric instability observed in rotating boson stars. Given the expected upper limits on scalar-field mass growth achievable through superradiance, our results suggest that rotating hairy black holes formed predominantly via this mechanism are likely to remain stable, at least up to the onset of the superradiant instability.

We show that the Starobinsky inflation model based on $R^2$ gravity has a special feature that provides a unique scalaron-two-graviton vertex with a coupling proportional to $1/M_P$. In this model, stochastic gravitational waves are produced when the scalaron, which is the massive scalar mode of the metric, decays into gravitons during reheating. This decay is accompanied by the decay of the scalaron into matter as well through a similar coupling, providing an efficient reheating. The stochastic gravitational waves thus produced have a characteristic strain $h_c\sim {10}^{-35}–{10}^{-34}$ in the frequency range ${10}^6–{10}^{12}\mathrm{Hz}$, which makes them accessible to resonant cavity searches for graviton-to-photon conversions. The detection of these high frequency gravitational waves would be a significant step in experimentally testing the Starobinsky inflation model.

In the cosmological Robertson-Walker geometry required of the cosmological principle both the Weyl tensor $C^{\mu \lambda \nu \kappa }$ and the Bach tensor $W^{\mu \nu }=[2{\nabla }_{\kappa }{\nabla }_{\lambda }-R_{\lambda \kappa }]C^{\mu \lambda \nu \kappa }$ vanish. In general, in perturbations around the cosmological background neither of the fluctuating $\delta C^{\mu \lambda \nu \kappa }$ or $\delta W^{\mu \nu }$ would vanish. However, it is possible for $\delta W^{\mu \nu }$ to vanish even as $\delta C^{\mu \lambda \nu \kappa }$ does not. In this paper we construct an explicit model in which this is the case. The model consists of a three-tensor gravitational wave fluctuating around a background with a constant negative three-curvature. The model is exactly solvable and consists purely of geometric quantities with no matter fields at all (i.e., $G^{\mu \nu }=0$, $\delta G^{\mu \nu }=0$, $W^{\mu \nu }=0$, $\delta W^{\mu \nu }=0$, where $G^{\mu \nu }$ is the Einstein tensor). The model can thus be created out of nothing, with creating a universe from nothing thus being an alternative principle to the cosmological principle. The fluctuating gravitational wave contributes to the temperature anisotropy in the cosmic microwave background and the $B$ mode polarization tensor in a calculable manner, one for which we provide a simple analytic way of treating spatial modes that is based on the use of a spatial mode addition theorem. In addition, we provide a treatment of the anisotropy that is based on the connection of bandwidth limited functions to signal processing theory, a treatment that is new to the literature. Classically by “nothing” we mean that there are no $T^{\mu \nu }$ or $\delta T^{\mu \nu }$ matter field terms. Quantum mechanically by “nothing” we mean that all fields other than the gravitational field are in a negative energy mode vacuum state, with the only occupied positive energy modes being graviton modes. These positive energy graviton modes can then excite negative energy particles out of the vacuum into positive energy states, to thus produce “something” with $\delta W_{\mu \nu }\ne 0$. As well as using the Bach tensor as a diagnostic, we consider dynamics based on it.

We analyze the latest cosmic microwave background (CMB) constraints on the scalar spectral index $n_s$ and tensor-to-scalar ratio $r$ from Planck 2018, BICEP/Keck 2018, the Atacama Cosmology Telescope Data Release 6 (ACT DR6), and the South Pole Telescope (SPT-3G) data, focusing on their implications for attractor models of inflation. We compare systematically observational bounds with theoretical predictions for both E-model ($\alpha$-Starobinsky) and T-model potentials. The observational constraints accommodate E-models with $\alpha \lesssim 25$, with the canonical Starobinsky model ($\alpha =1$) predicting $n_s=0.958–0.963$ for reheating temperatures between $100-{10}^{10}\mathrm{GeV}$, in good agreement with Planck 2018 data and within the 95% CL region determined by the Planck-ACT-SPT combination, but below the 95% confidence region of the Planck-ACT-DESI combination. Higher reheating temperatures from near-instantaneous reheating improve the compatibility. T-models predict slightly lower $n_s$ values (0.956–0.961), in some tension with Planck 2018 data, and we find an upper limit of $\alpha \lesssim 11$ in these models. We extend our analysis to generalized $\alpha$-attractors with monomial potentials $V(\phi )\propto {\phi }^k$ near the minimum, demonstrating that models with $k\ge 6$ naturally predict $n_s\simeq 0.965–0.968$ for typical number of $e$-folds, in better agreement with the ACT DR6 data. We also consider deformed E- and T-models, which allow significantly higher values of $n_s$ for low values of $\alpha \simeq 1$.

Fermi Large Area Telescope observations of gamma-ray pulsars can be used to build a pulsar timing array (PTA) experiment to search for gravitational wave (GW) signals at nanohertz frequencies. At those frequencies, the dominant signal is expected to be a stochastic gravitational wave background (GWB) produced by the incoherent superposition of the quasimonochromatic GW emissions from a population of supermassive black hole binaries. While the radio PTAs have recently announced compelling evidence for a GWB signal with a power law spectrum of strain amplitude $\approx 2–3\times {10}^{-15}$ (at the frequency of $1{\mathrm{yr}}^{-1}$), in 2022, an analysis of 12.5 years of Fermi data for 35 pulsars led to an upper limit of $1\times {10}^{-14}$ for the GWB amplitude. The analysis was carried out on times of arrival obtained by folding from six months up to one year of photon observations. A photon-by-photon approach was also tested to infer constraints on the GWB amplitude from individual pulsars, but without accounting for the cross-pulsar correlations that a GWB would induce. Here, we reanalyze the same dataset using a regularized likelihood method that correctly models cross-pulsar correlations directly from the photons, while additionally marginalizing over the uncertain pulse profile shape. While the two methods are not expected to have significant differences in sensitivity, we prove through simulations of gamma-ray PTA datasets that the photon-by-photon method for GWB recoveries is, statistically, more robust. The resulting upper limit obtained for the GWB strain amplitude is $1.2\times {10}^{-14}$, indicating that the improved method yields a consistent result with the previous analyses.

The final-parsec problem has long posed a central challenge in understanding the merger of supermassive black hole binaries. In this paper, we investigate a scenario in which a dark scalar or vector field is sourced by eccentric binaries, leading to accelerated mergers through additional dipole radiation and thereby extending the range of masses for which the binary can merge within a Hubble time. The Newtonian-order radiation fluxes from an eccentric charged Keplerian binary are derived using general results for localized periodic sources in flat spacetime. We find that dipole radiation, although insufficient to fully resolve the final-parsec problem, can alter the low-frequency spectrum of the stochastic gravitational wave background from supermassive black hole binary inspirals. We construct a simplified model for the spectrum and perform a Bayesian analysis using the current pulsar timing array data.

A novel experiment is introduced to detect photon-axion conversion independent of the dark-matter hypothesis in a broad mass-range called WISP Interferometer (WINTER). The setup consists of a free-space Mach-Zehnder-type interferometer incorporating an external magnetic field and vacuum in one of the arms, where photon-axion mixing occurs via the Primakoff effect and is detected through changes in amplitude. The expected axion-induced signal is then modulated by polarization changes. The experiment is designed to integrate a Fabry-Pérot cavity with a finesse of ${10}^5$ that will be operated in a vacuum environment, significantly enhancing the sensitivity. It is projected to reach the Dine-Fischler-Srednicki-Zhitnitsky theoretical line with photon-axion coupling sensitivities down to $g_{a\gamma \gamma }\simeq 3.7\times {10}^{-14}{\mathrm{GeV}}^{-1}$ for axion masses up to 380 μeV.

In order to improve the performance of the x-ray pulsar timing system and further refine the pulsar time series analysis process, we propose a Hankel-singular value decomposition (SVD) principal modal vector energy-fusion based phase delay estimation method for x-ray pulsar. First, the pulsar profile signal is subjected to Hankel embedding and singular value decomposition. The principal modal vector in the structured subspace is extracted from the one-dimensional profile signal, effectively suppressing redundant components such as observation noise. Secondly, cross-spectral analysis is performed on the standard and folded profiles in the main modal domain. Combining the phase ratio method, the phase difference of each frequency component is analytically solved. By utilizing the frequency-domain phase continuity, the resolution limitation caused by discrete search in the time domain is overcome, achieving subsampling level phase delay estimation below the sampling interval. Finally, combining the frequency energy distribution characteristics of each order, we propose a fusion strategy based on cross-spectral energy constraints, using spectral amplitude to construct weights. The phase shifts of each order are weighted and adjusted to further improve estimation accuracy. Meanwhile, we conduct ablation tests, computational complexity analysis, and influencing factor analysis on the proposed method. Furthermore, we perform ground-based experimental tests using actual observation data from the NICER and XPANV-1 satellites. The results show that compared to cross-correlation estimation and maximum likelihood estimation, our method improves estimation accuracy by 26.18% and 42.72%, respectively, and improves estimation stability by 16.91% and 43.88%, respectively. The proposed method has advantages such as high estimation accuracy, strong estimation stability, and subsampling level phase estimation resolution, providing important support for the development of high-precision pulsar timing.

Hyperon-antihyperon pairs produced from electron-positron annihilations provide a promising platform for exploring quantum-information properties in particle physics. In this work, we analyze quantum steering and quantum discord in hyperon-antihyperon systems produced from $e^{+}{e}^{-}$ annihilations, based on the $X$-shaped spin density matrix reconstructed via quantum state tomography. We show that the behaviors of these correlations differ from those observed in elementary particle-antiparticle systems such as top quarks and $\tau$ leptons, owing to the polarization effects specific to hyperon decays. From the results, we examine the hierarchy of quantum correlations in hyperon-antihyperon systems, $\mathrm{Bell}\mathrm{nonlocality}\subset \mathrm{steering}\subset \mathrm{entanglement}\subset \mathrm{discord}$. We also discuss the role of experimental loopholes and the impact of quantum decoherence in collider-based studies of quantum correlations.

In bound systems whose constituent particles are heavier than the electron, the dominant radiative correction to energy levels is given by light-fermion (electronic) vacuum polarization. In consequence, relativistic and recoil corrections to the one-loop vacuum-polarization correction are phenomenologically relevant. Here, we generalize the treatment, previously accomplished for systems with orbiting muons, to bound systems of constituents with more general spins: spin-0, spin-$1/2$, and spin-1. We discuss the application of our more general expressions to various systems of interest, including spinless systems (pionium), muonic hydrogen and deuterium, and devote special attention to the excited non-$S$ states of deuteronium, the bound system of a deuteron and its antiparticle. The obtained energy corrections are of order ${\alpha }^5{m}_r$, where $\alpha$ is the fine-structure constant and $m_r$ is the reduced mass.

We clarify selection rules of conjugacy classes of several finite discrete groups where we deal with both gauged and ungauged cases. We find that the selection rules enjoy finite Abelian or non-Abelian discrete symmetries originating from the inner and/or outer automorphism of underlying discrete groups. Since the selection rules of conjugacy classes do not obey conventional grouplike selection rules, they open up new coupling selection rules of fields which are labeled by the conjugacy classes.

We investigate a dark sector coupled to the Standard Model through a kinetically mixed dark photon $U$ associated with a new $U(1{)}^{\prime }$ gauge symmetry. Kinetic mixing, parametrized by $ϵ$, induces an effective coupling to the electromagnetic current, while the dark photon interacts with a stable dark matter (DM) particle $\chi$ through a dark gauge coupling $g_{\chi }$, defining a four-dimensional parameter space $(m_U,ϵ,m_{\chi },g_{\chi })$. Our analysis is based on the parton-hadron-string dynamics (PHSD) transport approach, extended to include dark photon production and decay into dileptons ($U\to e^{+}{e}^{-}$). In PHSD, dark photons are produced in high-energy collisions through Dalitz decays of light mesons (${\pi }^0,\eta ,{\eta }^{\prime },\omega$), delta resonances ($\mathrm{\Delta }\to NU$), direct vector meson decays ($\rho ,\omega ,\varphi \to U$), kaon decays ($K^{+}\to {\pi }^{+}U$), and $q\overline{q}\to U$ annihilation. Building on previous PHSD benchmarks against dilepton data, we extract upper limits on ${ϵ}^2(m_U,m_{\chi },{\alpha }_{\chi })$ in both the visible regime ($m_U<2m_{\chi }$), where $U\to e^{+}{e}^{-}$ dominates, and the invisible regime ($m_U>2m_{\chi }$), where $U\to \chi \overline{\chi }$ is kinematically open and suppresses the dilepton branching fraction. Cosmological and astrophysical constraints are incorporated in two complementary ways. First, we compute the velocity-dependent self-interaction cross section $\sigma /m_{\chi }$ for Yukawa-Mediated self-interacting dark matter and confront it with bounds from dwarf galaxies, galaxy groups, and clusters. Second, we determine thermal relic target curves by computing the relic abundance and requiring ${\mathrm{\Omega }}_{\mathrm{DM}}{h}^2\simeq 0.12$, consistent with Planck measurements of the cosmic microwave background. Combining PHSD limits on ${ϵ}^2$ with relic density and self-interaction requirements, we exclude regions of the $(m_{\chi },m_U)$ plane for each DM realization (Dirac fermion, Majorana fermion, or complex scalar) and identify benchmark scenarios in which heavy-ion, cosmological, and astrophysical constraints are simultaneously satisfied.