A comprehensive analysis of $\pi K\to \pi K$ and $\pi \pi \to K\overline{K}$ amplitudes at large unphysical pion mass for all important partial waves is presented. A set of crossing-symmetric partial-wave hyperbolic dispersion relations is used to describe lattice quantum chromodynamics (QCD) data at $m_{\pi }=391\mathrm{MeV}$. In the present analysis, the amplitudes for the $S$- and $P$-waves are formulated by combining the constraints of analyticity, unitarity, and crossing symmetry, fulfilling Roy-Steiner-type equations. We use these results to investigate the low-lying strange-meson resonances and resolve the instability problem tied to analytic continuation in prior lattice QCD studies based on the $K$-matrix formalism. At $m_{\pi }=391\mathrm{MeV}$, the rigorous Roy-Steiner-type equation approach allows us to determine the $S$-wave scattering lengths, $m_{\pi }{a}_0^{1/2}=(0.92_{-0.28}^{+0.06})$, $m_{\pi }{a}_0^{3/2}=-(0.32_{-0.02}^{+0.05})$, and the $\kappa$ [also known as $K_0^{*}(700)$] pole position, $\sqrt{s_{\kappa }}=(966_{-24}^{+41}-i198_{-17}^{+38})\mathrm{MeV}$. We also provide a detailed analysis of the complex validity domain of the Roy-Steiner-type equations.

We perform a causality analysis on the dispersion relation of hydrodynamics with spin as well as shear and bulk viscosity, including the relaxation times for all these quantities. We find that the interplay of the three relaxational scales, for shear and bulk viscosity as well as polarization, leads to nontrivial effects on the dispersion relation. Unexpectedly, the presence of polarization leads to lower effective viscosity and a longer relaxation time, and the presence of viscosity leads to lower limits as well as upper ones on the group velocity and constraints relating polarization to viscosity relaxation times. We conclude with a qualitative discussion on how these results impact phenomenology, specifically the low effective viscosity in strongly interacting matter as well as shear-vorticity coupling.

We analyze the pole expansion of the two-hadron imaginary-time correlation function. We first explain the general idea that the imaginary-time correlation function is expressed as a sum of the pole terms, the Mittag-Leffler expansion, in terms of the uniformization variable, which makes the S-matrix single-valued. We then derive explicit expressions of the pole expansion for the single-channel ($\rho$ meson) and two-channel [$\mathrm{\Lambda }(1405)$] examples and demonstrate that the pole expansion actually holds employing phenomenological models, the vector-dominance model for the $\rho$ meson and the chiral unitary model for $\mathrm{\Lambda }(1405)$. From this observation we propose the pole expansion as a method to extract information of unstable states such as masses and widths from the two-hadron imaginary-time correlation functions obtained by lattice quantum chromodynamics (QCD) simulations.

We evaluate the pion and kaon transverse momentum dependent parton distribution functions in the instanton liquid model, a model of the QCD vacuum at low resolution. The relevant transverse momentum distributions (TMDs) are factored into a constituent quark distribution times a rapidity dependent soft factor from staple-shaped Wilson lines, for fixed parton longitudinal momentum and transverse separation. The results are evolved to higher rapidities using the Collins-Soper kernel and higher resolution using renormalization group evolution. The comparison to existing extractions of pion TMDs from Drell-Yan data is briefly discussed.

Recently, a number of exotic hadrons have been reported in the experiments, and most of these states lie slightly below the threshold. Therefore, these states are considered to be hadronic molecules composed of mesons or baryons. In 2022, the doubly charmed tetraquark $T_{cc}$ was reported by the LHCb experiment, which is considered to be composed of two heavy quarks and two light antiquarks, and located slightly below the $D{D}^{*}$ threshold. The observation motivates us to study the bound and resonant states of the doubly heavy tetraquarks as two meson systems. We employ the one boson exchange potential as an interaction between two mesons, where one free parameter has been determined to reproduce $T_{cc}$ reported by the LHCb experiment. In our previous work, bound states of $D^{(*)}{D}^{(*)}$ and $B^{(*)}{B}^{(*)}$ molecules were studied, where we respected the heavy quark spin symmetry (HQS). Using the same framework, we study not only bound but also resonant states with $J\le 2$ in this paper. Furthermore, we discuss the HQS partner structures of $T_{cc}$ and $T_{bb}$ obtained in our study by introducing the light cloud basis.

The hadron physics community has been actively debating the interpretation of so-called mechanical properties of hadrons. Nonrelativistic quantum-mechanical systems like the hydrogen atom have been appealed to in these debates as analogies. Since such appeals are likely to continue, it is important to have Galilei-covariant expressions for matrix elements of the energy-momentum tensor. In this work, I obtain Galilei-covariant breakdowns of such matrix elements into mechanical form factors, with a special focus on spin-half states. I additionally study the spatial densities associated with these form factors, using the pilot wave interpretation to guide their breakdown into contributions from internal structure and from quantum-mechanical effects such as wave packet dispersion. For completeness, I also obtain nonrelativistic Breit frame densities.

We present a study of the central exclusive production (CEP) of $\eta$ and ${\eta }^{\prime }(958)$ mesons in diffractive proton-proton collisions at high energies. The amplitudes, including pomeron and $f_{2\mathbb{R}}$ reggeon exchanges, are calculated within the tensor-pomeron model. Absorption effects are also taken into account at the amplitude level. We fit some undetermined model parameters (coupling constants and cutoff parameters in form factors) to the WA102 experimental data and then make predictions for the LHC energy $\sqrt{s}=13\mathrm{TeV}$. Both total cross sections and several differential distributions are presented. For $pp\to pp\eta$, we find an upper limit for the total cross section of $2.5\mathrm{\mu }\mathrm{b}$ for pseudorapidity of the $\eta$ meson $|{\eta }_M|<1$ and $5.6\mathrm{\mu }\mathrm{b}$ for $2<{\eta }_M<5$. For $pp\to pp{\eta }^{\prime }$, we predict the cross section to be in the range of $0.3–0.7\mathrm{\mu }\mathrm{b}$ for pseudorapidity of the ${\eta }^{\prime }$ meson $|{\eta }_M|<1$ and $0.9–2.1\mathrm{\mu }\mathrm{b}$ for $2<{\eta }_M<5$. This opens the possibility to study diffractive production of pseudoscalar mesons in experiments at the LHC. We discuss if there are arguments from SU(3)-flavor symmetry which would forbid pomeron-pomeron fusion giving an $\eta$ meson. In our opinion such arguments do not exist. We also consider CEP of the pseudoscalars $\eta$ and ${\eta }^{\prime }(958)$ and the pseudovector meson $f_1(1285)$ in diffractive proton-proton collisions in a theory with a scalar pomeron. We show that none of these particles can be produced in this way in the scalar-pomeron theory. Thus, experimental observation of any of these particles in the above CEP processes at the LHC would give striking evidence against a scalar character of the pomeron.

Determining the spatial curvature (${\mathrm{\Omega }}_{\mathrm{k}}$) independent of cosmic microwave background observations plays a key role in revealing the physics of the early Universe. The Hubble tension is one of the most serious issues in modern cosmology. We investigate halo catalogs identified from $N$-body simulations at $z=2$ and 3, mimicking high-redshift galaxy surveys. We measure redshift-space correlation functions of halos from the two snapshots. We detect clear features of baryon acoustic oscillations and redshift-space distortions. We find that we can obtain a few percent constraints on both the geometric distances and growth of structure at the distant universe in future surveys. By taking into account the information of the underlying matter power spectrum, we demonstrate that we can also achieve constraint on the Hubble constant $H_0$ with a few percent as well as the spatial curvature with $|{\mathrm{\Omega }}_{\mathrm{k}}|\lesssim 0.1$ by observing galaxies with the number density with ${\overline{n}}_{\mathrm{g}}\simeq {10}^{-4}(h^3{\mathrm{Mpc}}^{-3})$. Our analysis provides a timely forecast for the upcoming spectroscopic surveys, which target emission line galaxy or dusty star-forming galaxy samples.

In a recent work [New chiral structures for baryon number violating nucleon decays, arXiv:2504.14855.] we identified generic baryon-number-violating (BNV) structures containing triple light quarks and achieved their leading-order chiral realizations involving octet pseudoscalars and baryons. Although many two-body nucleon decays into a vector meson have been experimentally searched for and stringently constrained, a consistent theoretical framework for their calculation is still lacking. In this Letter, we fill the gap by implementing chiral matching of all these triple-quark interactions onto hadronic interactions involving octet vector mesons, baryons, and pseudoscalars. This paves the way for a consistent and comprehensive study of all relevant BNV processes. As an illustration of application, we show how degeneracy in the parameter space of Wilson coefficients can be broken by synthesizing experimental constraints on nucleon decays into a vector or pseudoscalar meson when relevant hadronic low-energy constants can be reasonably determined.

Using the subtraction approach, we give the bipartite mixed state entanglement entropy in thermal conformal field ${\text{theory}}_2$. With these entanglement entropies, we examine in detail the holographic duals of different entangling configurations unambiguously. In the thermofield double state, we show an horizon-crossing feature in two-sided entanglement configuration.

We unify the dynamics of massive vector (Proca) fields in Schwarzschild spacetime with supersymmetric gauge theories through the Seiberg-Witten/quasinormal mode (SW/QNM) duality. By mapping Proca perturbations—specifically monopole and odd-parity modes governed by confluent Heun equations—to the quantum Seiberg-Witten curve, we establish a gauge-gravity correspondence. Leveraging instanton counting, we analytically compute QNM and quasibound state frequencies to high precision, resolving spectral properties nonperturbatively. Our results align with numerical benchmarks while extending the SW framework beyond scalar fields.

In this work, we revisit the exact computation of the round sphere partition function of 3d $\mathcal{N}=4$ circular quiver Chern-Simons theories with mass and Fayet-Iliopoulos (FI) deformations. Utilizing the Fermi gas formalism, we derive the large $N$ expansion of the partition function and determine the Airy function structure, parametrized by three functions $C$, $B$, and $A$. We propose a novel closed-form expression for $A$ that incorporates the effects of FI parameters and satisfies various consistency constraints from quiver reductions. As an application, by using an accidental coincidence of the Fermi gas density matrices we extend our results to the squashed sphere partition function of $\mathcal{N}=4$ super Yang-Mills theories with an adjoint hypermultiplet and multiple fundamental hypermultiplets. Our findings provide further evidence for the universality of the Airy function structure in supersymmetric gauge theories of multiple M2-branes.

Gravitational waves from the coalescence of compact objects carry information about their dynamics and the spacetime in regions where they are evolving. In particular, late-time tails and memory effects after the merger are two low-frequency phenomena, not detectable by current instruments, but which can be observed by future detectors. Their low-frequency nature could, in principle, make them more sensitive to larger-scale structures at galactic length scales. We show that indeed there are transient features, such as amplitude changes, in both tails and (linear) memory when the merger occurs while immersed in an astrophysical environment. For realistic galaxies, the environment’s compactness is small enough that the effect is strongly suppressed, but these effects could become relevant for mergers occurring in regions with matter overdensities, like the ones recently observed numerically for wave dark matter. On the other hand, the memory (the difference between the amplitude asymptotically early and late) and asymptotically late decay are independent on the properties of the environment.

We investigate the cosmological impacts of the alternative effective mass function of the modified Mukhanov-Sasaki equation in loop quantum cosmology, which is obtained from the polymerization of the classical mass function derived in the comoving gauge. This alternative effective mass function is distinct from those in the dressed metric and the hybrid approaches and is able to generate a new structure in the primordial power spectrum. After taking the Starobinsky potential and employing a particular polymerization ansatz for the inverse Hubble rate, the effective mass function is characterized by a free parameter $\xi$. When $\xi \ge 0.1$, there appears a wave-packet structure in the region preceding the almost scale invariant regime of the power spectrum and both the location and the height of the wave packet are affected by the choice of $\xi$. For the angular power spectrum, we find $\xi =0.2$ provides a curve practically indistinguishable from the one of $\mathrm{\Lambda }\mathrm{CDM}$ model. Our study presents a concrete example in which the fine structure of the primordial power spectrum sensitively relies on the parameters in the polymerization ansatz.

We investigate the conditions under which a hypersurface becomes null through the use of coordinate transformations. We demonstrate that, in static spacetimes, the correct criterion for a surface to be null is $g_{tt}=0$, rather than $g^{rr}=0$, in agreement with the results of Vollick. We further show that, if a Kruskal-like coordinate exists, the proxy condition $g^{rr}=0$ is equivalent to $g_{tt}=0$ if ${\partial }_r{g}_{tt}\ne 0$ and both $g^{rr}$ and $g_{tt}$ vanish at the same rate near the horizon. Our method extends naturally to axisymmetric stationary spacetimes, for which we demonstrate that the condition $\det (h_{ab})=0$ for the induced metric on a null hypersurface is recovered. By contrast with the induced metric approach, our method provides a physical perspective that connects the general null condition with its underlying relationship to photon geodesics.

Future x-ray missions, such as NICER and LOFT, together with gravitational-wave observations from ground-based detectors, will provide new insights into neutron stars. Interpreting accurate observations in the future will require accurate models of their gravitational fields. In this first paper of a two-part series, we construct the perturbation equations for slowly rotating, isolated, and unmagnetized neutron stars, extending the Hartle-Thorne approximation to seventh order in a slow-rotation expansion. We obtain exact, closed-form, analytical solutions for the exterior metric at each order in spin. From these solutions, we derive expressions for the mass and mass-current scalar multipole moments, $M_{\ell }$ and $S_{\ell }$, respectively, up to seventh order in spin frequency, using two distinct methods. This high-order expansion allows us to calculate second-, fourth-, and sixth-order relative spin corrections to the observed mass and moment of inertia; second- and fourth-order relative spin corrections to the quadrupole and octopole moments; second-order relative spin corrections to the hexadecapole and dotriacontapole moments; and leading-order-in-spin expressions for the hexacontatetrapole and hectoicosaoctapole moments. Going to seventh order in the spin-frequency approximation will enable very precise calculations of x-ray pulse profiles, as well as the I-Love-Q and three-hair relations for slowly rotating neutron stars. These results will be valuable for breaking parameter degeneracies in future multimessenger observations.

The increasing sensitivity of current and upcoming gravitational-wave (GW) detectors poses stringent requirements on the accuracy of the GW models used for data analysis. If these requirements are not met, systematic errors could dominate over statistical uncertainties, hindering our ability to extract astrophysical and cosmological information, and conduct precise tests of general relativity. In this work, we present a novel method to mitigate the impact of waveform-systematic errors, by incorporating and marginalizing over waveform-uncertainty estimates, which are modeled as probability distributions for the numerical-relativity calibration parameters of effective-one-body waveform models. By analyzing simulated GW signals of loud “golden” binary-black-hole systems, we show that our method significantly reduces biases in the recovered parameters, highlighting its potential to improve the robustness of GW parameter estimation with upcoming observing runs and next-generation ground-based facilities, such as the Einstein Telescope and Cosmic Explorer.

We explore the effects of gravitational waves (GWs) on hydrogen’s radio spectral lines, focusing on the ground-state hyperfine transition and radiative transitions in highly excited Rydberg states. To analyze GW impacts on hyperfine structure, we derive Maxwell’s equations in a gravitational-wave background using linearized gravity and the $3+1$ formalism. Our findings reveal that GWs induce energy shifts in hyperfine magnetic substates, modifying the 21 cm line. However, these energy shifts fall well below the detection limits of current radio astronomical instruments. For transitions in highly excited states, which produce radio recombination lines (RRL), the influence of GW manifests itself as spectral broadening, with the fractional linewidth for $\mathrm{H}n\alpha$ scaling as $\mathrm{\Delta }\nu /{\nu }_0\sim n^7{\omega }_{\mathrm{gw}}^{2}h(t)$. This suggests that RRLs could serve as probes for ultra-high-frequency GWs, particularly given that Rydberg atoms in the interstellar medium can reach quantum numbers above $n=100$. As an example of possibly detectable high frequency GW source, We investigate GWs emitted during the inspiral of planetary-mass primordial black hole binaries, where GW-induced broadening in RRLs could exceed natural broadening effects. Additionally, we examine the influence of the recently detected stochastic gravitational-wave background on hydrogen spectral lines.

Classical gravity theory predicts a state-dependent gravitational potential for a quantum test mass, leading to nonlinear Schrödinger-Newton (SN) state evolution that contrasts with quantum gravity. Testing the effect of SN evolution can provide evidence for distinguishing quantum gravity and classical gravity, which is challenging to realize in the stationary optomechanical systems as analyzed in previous works [Yubao Liu, Haixing Miao, Yanbei Chen, and Yiqiu Ma, Semiclassical gravity phenomenology under the causal-conditional quantum measurement prescription, Phys. Rev. D 107, 024004 (2023).; Yubao Liu, Wenjie Zhong, Yanbei Chen, and Yiqiu Ma, Semiclassical gravity phenomenology under the causal-conditional quantum measurement prescription. II. Heisenberg picture and apparent optical entanglement, Phys. Rev. D 111, 062004 (2025).]. This Letter is devoted to analyzing the possibility of capturing the signature of SN theory during the nonstationary evolution of the test mass under the optomechanical measurement, where the second-order moments of a test mass can exhibit a distinctive oscillatory behavior. We show that this feature manifests in the nonstationary noise spectrum of outgoing light as additional peak structures, although resolving these structures in practical experiments requires a larger number of repetitive trials with our sampling parameters, which is cost prohibitive. To address this issue, we further employ statistical inference methods to extract more comprehensive information, thereby reducing the required number of experimental repetitions. Through mock data simulations, we demonstrate that only ten experimental trials of 40 sec each are sufficient to reduce the false alarm rate for distinguishing between the two models to below 1%.

White dwarfs (WDs) can be used as laboratories to test strong gravity and high-density regimes, once their equation of state is not so uncertain as the one of neutron stars. This makes them also a useful tool to constrain dark-matter models. In this work, we study dark matter white dwarfs (DMWD) composed of white dwarf matter admixed with fermionic dark matter in a two-fluid general relativistic framework. Dark matter particles are considered to have masses between 0.1–10 GeV. The equilibrium configurations and stability are derived, showing that the DMWD can be more compact, with masses around $1.3M\odot$ and radii around 500 km. The increasing compactness leads to changes in the fundamental modes of radial oscillations ($\sim 20\%$ for 0.1 GeV DM), which produce detectable shifts in GW frequencies. The interplay between dark matter and normal matter thus provides a compelling avenue for interpreting deviations in observed WD properties and for placing constraints on DM characteristics through astrophysical observations.