We investigate the domain in which a semiclassical gravitational Wentzel–Kramers–Brillouin (WKB) flow can serve as a quantitatively controlled temporal reference for subordinate quantum degrees of freedom. Rather than introducing WKB time at the outset, we formulate the Born-Oppenheimer adiabatic condition directly on gravitational configuration space using the Hamilton-Jacobi vector field. This separates adiabatic control from the local WKB validity of the gravitational branch and from the sharpness of the candidate reference against quantum fluctuations. For a single selected semiclassical branch, these requirements define the validity domain ${\mathcal{D}}_t={\mathcal{D}}_{\mathrm{WKB}}\cap {\mathcal{D}}_{\mathrm{ad}}\cap {\mathcal{D}}_{\text{sharp}},$ with an additional decoherence condition when coherent branches coexist. In a closed Friedmann-Robertson-Walker (FRW) minisuperspace coupled to a homogeneous massive scalar mode, the distinction is explicit: approaching the gravitational turning point from the oscillatory region, the ordinary WKB control parameter diverges while the configuration-space adiabatic parameter tends to zero. A uniform Airy treatment of the turning point removes the formal WKB divergence while preserving the inequivalence: the corresponding local control parameter remains of order unity, whereas the configuration-space adiabatic parameter is parametrically suppressed as $O(M^{-1/3})$. Thus Born-Oppenheimer adiabaticity and gravitational WKB validity define inequivalent domains even within the simplest minisuperspace model. We conclude that the existence of an oscillatory semiclassical branch is not sufficient for a reliable WKB temporal description: semiclassical temporal reliability is instead determined by the overlap of the validity domains supporting the reference flow.

We constrain Einstein-æther gravity—a Lorentz-violating extension of general relativity in which a dynamical, unit timelike vector field selects a preferred frame—using updated high-precision pulsar timing observations of PSR $\mathrm{J}1738+0333$ from the European Pulsar Timing Array second data release and the North American Nanohertz Observatory for Gravitational Waves 9-year release, in combination with times of arrival from Arecibo, Green Bank, Nançay, Parkes, and Westerbork. Our method accounts for both conservative and dissipative first post-Newtonian corrections arising from Lorentz violation; here, we apply it to PSR $\mathrm{J}1738+0333$ using the Bayesian timing pipeline Vela to process the full time-of-arrival data set. We sample the joint posterior over binary component masses, post-Keplerian parameters, and center-of-mass velocity components, and then apply a resampling scheme to propagate posteriors into robust constraints on the fundamental theory parameters, obtaining the most stringent strong-field bounds on the Einstein-æther coupling constants from a single binary pulsar system to date.

It has been shown that the thermodynamics of frame-invariant scalar-tensor gravity admits an Einstein-frame-like invariant representation, in which the scalar sector is minimally coupled and behaves as a perfect fluid with vanishing temperature. We show that this is not the only invariant thermodynamic organization available. Using instead the invariant matter metric, we construct a Jordan-frame-like invariant representation in which matter is minimally coupled and the gravitational action takes the Brans-Dicke-Bergmann-Wagoner form with invariant fields $\mathrm{\Psi }={\mathcal{I}}_1^{-1}$, $\mathcal{U}(\mathrm{\Psi })$, and ${\omega }_{\mathrm{inv}}(\mathrm{\Psi })$. In this representation, the metric field equations retain the Hessian sector characteristic of Jordan-frame scalar-tensor gravity. A $1+3$ decomposition of the corresponding effective stress tensor yields nonvanishing heat flux and anisotropic stress in a generic congruence. In the $\mathrm{\Psi }$-comoving frame, the usual first-order thermodynamic identifications are recovered in invariant form, including $K_{\mathrm{J}}{T}_{\mathrm{J}}=-\dot{\mathrm{\Psi }}/({\kappa }^2\mathrm{\Psi })$ and ${\eta }_{\mathrm{J}}=\dot{\mathrm{\Psi }}/(2{\kappa }^2\mathrm{\Psi })$, with the bulk channel obtained in homogeneous and isotropic sectors. Thus, frame-invariant scalar-tensor thermodynamics is not intrinsically restricted to an Einstein-frame-like perfect-fluid description: it also admits a Jordan-frame-like invariant formulation in which the effective imperfect-fluid interpretation is manifest.

Cosmological inference using a population of binary black-hole mergers, combined with a galaxy catalog, presents an exciting opportunity for precision cosmology with the possibility of resolving the Hubble tension. However, the accuracy of these measurements heavily relies on the quality of the model used to infer the binary parameters, including the model of the gravitational-wave signal. We use state-of-the-art quasicircular, multipolar, spin-precessing waveform models, including mode asymmetries, to explore the impact of inaccurate modeling in measuring the Hubble-Lemaître constant for the upcoming and future ground-based gravitational-wave observatories. We diagnose the presence of inaccuracies within a hierarchical population-analysis framework, without a priori knowing the true value of the parameter, by assessing the consistency of the distribution of individual posteriors in relation to their measurement errors. Our findings indicate that even a small high-mass, spin-precessing subpopulation—comprising as little as 2% of the population generating the events observed by the LIGO-Virgo-KAGRA Collaboration so far—can result in an unreliable measurement of the Hubble-Lemaître constant in the upcoming observing runs of these detectors, with even more pronounced effects expected in future facilities on the ground. Crucially, we find systematic biases across a wide range of waveform models, rather than for only a specific signal-template pair.

It has been observed that the Universe is permeated by the cosmic photon background, ranging from radio waves to gamma rays. We investigate the conversion of the photon background into gravitons in the presence of background magnetic fields in the Milky Way Galaxy and in blazar jets. We find that the resulting graviton background is dominated by the contribution generated in blazar jets. Importantly, this graviton background constitutes a graviton floor for high-frequency gravitational wave detectors searching for new physics, analogous to the neutrino floor.

$g$ mode resonances in eccentric binary neutron star systems are potential probes of internal stratification, superfluidity, composition gradients, and the equation of state. Although such weak dynamical tidal signatures are unlikely to be resolved with current detector sensitivities, third generation observations may make them accessible, in which case identifying the weak resonant phase shift would provide information beyond the bulk adiabatic tidal deformability. We build a four class dataset in an eccentric harmonic framework, containing point particle, adiabatic tide, resonant $g$ mode, and pure noise samples, and use Einstein Telescope (ET) and Cosmic Explorer (CE) detector data to test whether this weak resonant phase signature can be identified from noisy time domain strain. The ET, CE, and $\mathrm{ET}+\mathrm{CE}$ deep learning models reach accuracies of 0.650, 0.809, and 0.875, respectively. On the same simulated samples, the matched filtering method reaches lower accuracies of 0.534, 0.703, and 0.718. This result arises from the fact that the resonant correction manifests as a weak phase morphology difference superimposed on the adiabatic tidal background, whereas matched filtering is sensitive only to the overall similarity. Hence, in the presence of weak phase differences, the neural network employed for the classification task is better able to learn these local phase and morphology features from the complete time domain strain segment. The results indicate that joint third generation observations improve the identifiability of weak internal mode phase information.

We conduct an investigation into the possible correlation between very-high-energy (VHE, $E>0.1\mathrm{TeV}$) gamma-ray sources, as identified by the Large High Altitude Air Shower Observatory (LHAASO), and high-energy neutrino events captured by the IceCube Neutrino Observatory. For this analysis, we utilize the First LHAASO catalog, which comprises 90 VHE gamma-ray sources, and the IceCube Event Catalog of Alert Tracks (IceCat-1), which includes 348 tracklike neutrino events. Through Monte Carlo simulations, we assess the correlations between the neutrino events and LHAASO sources, achieving the best $p$-values of 0.237, 0.312, and 0.115, respectively, for all LHAASO sources, KM2A sources, and WCDA sources. These findings imply that the spatial coincidence between LHAASO sources and neutrino alerts is relatively weak. Furthermore, under the assumption that gamma rays are exclusively generated through hadronic interactions, we estimate the most optimistic theoretical neutrino fluxes from LHAASO sources and compare them with the IceCube observed fluxes. The results indicate that the majority of these sources are improbable counterparts to the detected neutrinos. In conclusion, LHAASO sources could be potential galactic neutrino emitters but currently do not exhibit compelling evidence, thereby underscoring the necessity for elevated sensitivity levels in forthcoming detection instruments like IceCube-Gen2.

Neutrino flavor conversion profoundly impacts the explosion mechanism and multimessenger emission of core-collapse supernovae. Yet, state-of-the-art hydrodynamic simulations of neutrino-dense astrophysical environments cannot account for neutrino quantum kinetics, necessitating subgrid schemes to model the impact of neutrino self-interaction on the quasisteady flavor configuration. We present semianalytic approximations for the outcomes of both slow and fast flavor conversions in quasihomogeneous systems with periodic boundary conditions. Independent of the mass ordering, our ansatz demonstrates excellent agreement with multiangle and multienergy solutions of the neutrino kinetic equations across a wide range of representative (anti)neutrino distributions.

We investigate a novel type of asymmetric dark matter (ADM) model in which the dark matter asymmetry and the baryon asymmetry in our Universe (BAU) are produced simultaneously via low-scale spontaneous leptogenesis, where the mass scale of right-handed neutrino is much lower than the Davidson–Ibarra bound $M_1\ll {10}^9\mathrm{GeV}$. In our scenario, both asymmetries are predominantly sourced by a dynamical $CP$ phase, namely, the Majoron. Its kinetic misalignment provides a sufficiently large, time-dependent effective $CP$ phase, allowing efficient asymmetry production even for low-scale right-handed neutrinos. In our framework, the sources of $CP$ violation responsible for the BAU and ADM are correlated with each other, leading to a predictive relation for the dark matter mass. In particular, when the dark matter asymmetry reaches its equilibrium value before freeze-out, the dark matter mass is typically predicted to lie in the range $\mathcal{O}(0.1)\mathrm{GeV}\lesssim m_{\chi }\lesssim \mathcal{O}(100)\mathrm{GeV}$, which lies within the sensitivity of direct detection experiments. On the other hand, if the dark matter asymmetry does not reach its equilibrium value due to weak coupling, the allowed mass range extends over a broader interval, $\mathcal{O}(0.1)\mathrm{GeV}\lesssim m_{\chi }\lesssim \mathcal{O}(10)\mathrm{TeV}$.

The unification of quantum theory and general relativity suggests the existence of a minimal measurable length, leading to a generalized uncertainty principle (GUP) and an energy-dependent vacuum group velocity. Testing these effects with macroscopic objects typically encounters the “soccer-ball problem,” where applying Planck-scale deformations to the total momentum predicts observationally ruled-out velocity deviations. We adopt the prescription, natural in quantum field theory, in which the GUP modifies single-mode commutators, and verify by explicit calculation that the macroscopic group velocity of a multimode coherent pulse reduces to the single-photon GUP velocity evaluated at the central wavelength, multiplied by the classical Gaussian-beam factor, with no dependence on the total pulse energy. The energy–momentum relation $E=pc$ itself is unmodified; the deformation enters through the velocity–momentum relation and is equivalent to a modified dispersion relation in the wave vector, with a quadratic coefficient that depends on which of the two variables is used. The soccer-ball problem—which arises only when the GUP is applied to the center-of-mass momentum of a composite system—is therefore absent for coherent light, and macroscopic petawatt pulses probe the same parameter space as single high-energy photons. Building on this framework, we propose a two-color vacuum chronoscopy experiment using a short-pulse petawatt laser and its high-harmonic generation. By systematically varying the macroscopic beam waist, our setup separates Planck-scale kinematic shifts from classical diffraction delays, establishing a controlled, source-independent terrestrial methodology whose sensitivity we assess against current astrophysical bounds and against the dominant waist-independent systematics that limit it, residual-gas dispersion and the harmonic birth-time offset.

Precision atomic spectroscopy provides a sensitive probe of physics beyond the Standard Model. A recently reported $9\sigma$ theory-experiment discrepancy in the ionization energy of metastable helium has motivated the hypothesis of a new boson mediating exotic electron-electron interactions. Using a general sign-consistency analysis of the induced energy shifts, we show that the sign requirement alone excludes vector-vector and pseudoscalar-pseudoscalar interactions as possible explanations of the anomaly. Incorporating existing constraints together with independent limits obtained in this work further excludes axial-vector scenarios. Within the single-boson framework considered in this work, only a narrowly constrained scalar-mediated interaction remains viable. The remaining parameter space could be probed in several different ways—for example, by modest improvements in the determination of the electron gyromagnetic ratio.

Modified dispersion relations arising in Lorentz-violating effective field theories alter the propagation of free particles and lead to observable deviations from standard relativistic kinematics. We show that, under regularity and nondegeneracy conditions, such kinematical modifications naturally induce local pseudo-Finsler geometric structures governing the free-particle propagation. The pseudo-Finsler framework provides a geometric interpretation of Lorentz invariance violation effects, encoding them in branch-dependent structures on spacetime. The construction is illustrated in the massive sectors of the standard model extension, where modified dispersion relations define local pseudo-Finsler geometries determined by the particle species acting as a spacetime probe. In this setting, we therefore construct a perturbative proof of the Kostelecký conjecture in all the physical massive subsectors of the standard model extension.

A quantitative investigation into the modification of ground-state field structures in two-color QCD (${\mathrm{QC}}_2\mathrm{D}$) is presented at finite chemical potential. Using lattice simulations with Wilson gauge and fermion actions, we explore the chromo-electromagnetic field strengths under varying matter densities. To ensure accurate measurements, we develop and calibrate two highly improved topological charge operators and evaluate four gradient flow actions. Our results reveal a finite-volume crossover in the regime of the anticipated phase boundary at $\mu =m_{\pi }/2$, with both chromoelectric and chromomagnetic field strengths suppressed before recovering and exceeding vacuum values at higher chemical potentials. We find the difference between the squared chromoelectric and chromomagnetic field strengths, $E^2-B^2$, to increase in magnitude monotonically with increasing chemical potential. At $a\mu =0.7$, we find an 11% suppression of $E^2$, a relatively small effect. A systematic analysis using sigmoid fits of lattice simulations in the crossover regime is performed to confirm the critical chemical potential obtained from the field structure is in agreement with the phase boundary at $m_{\pi }/2$. These findings provide new insight into non-Abelian ground-state vacuum field structures and offer a foundation for future studies in real QCD.

We demonstrate the use of the gradient flow combined with the short flow-time expansion ($\mathrm{GF}+\mathrm{SFTX}$) as a renormalization procedure for four-quark operator matrix elements and associated bag parameters relevant to neutral heavy-meson mixing ($\mathrm{\Delta }Q=2$) and heavy-meson lifetimes ($\mathrm{\Delta }Q=0$). Using six RBC/UKQCD $2+1$-flavor domain-wall fermion ensembles, we calculate for a charm-strange system with physical quark masses flowed bag parameters and match them to the $\overline{\mathrm{MS}}$ scheme using perturbative SFTX coefficients up to next-to-next-to-leading order in QCD. We employ a multiscale matching strategy and a renormalization-group improved flow-time evolution which allows for a reliable estimate of systematic uncertainties. For a fictitious neutral $D_s$ meson, we obtain the $\mathrm{\Delta }Q=2$ $\overline{\mathrm{MS}}$ bag parameter ${\mathcal{B}}_1^{\overline{\mathrm{MS}}}(3\mathrm{GeV})=0.7673(123)$, consistent with existing short-distance $D^0$ mixing determinations. For the $\mathrm{\Delta }Q=0$ lifetime-ratio operator basis, we find the $\overline{\mathrm{MS}}$ results $B_1^{\overline{\mathrm{MS}}}(3\mathrm{GeV})=1.0524(97)$, $B_2^{\overline{\mathrm{MS}}}(3\mathrm{GeV})=0.9621(71)$, ${\epsilon }_1^{\overline{\mathrm{MS}}}(3\mathrm{GeV})=-0.2275(76)$, and ${\epsilon }_2^{\overline{\mathrm{MS}}}(3\mathrm{GeV})=-0.0005(8)$. We provide conversion formulae to reexpress these results for an arbitrary choice of evanescent operators. These results demonstrate that $\mathrm{GF}+\mathrm{SFTX}$ can deliver precise determinations of dimension-six four-quark operators and establish a framework for future lattice computations including more complex operator bases, where the challenge of power-divergent mixing is shifted to the continuum and handled in the SFTX.

The quantum simulation of topological phases in $(2+1)\mathrm{D}$ quantum electrodynamics with Wilson fermions provides a promising route toward realizing topological phenomena in near-term lattice experiments. We show that the commonly used staggered-fermion discretizations in Hamiltonian gauge theories possesses an exact time-reversal symmetry, which forbids the emergence of nontrivial topological phases and has led to confusion in the existing literature. In this work, we resolve this obstacle by systematically analyzing fermion discretization effects in $(2+1)\mathrm{D}$ lattice Hamiltonians of fermions coupled to U(1) gauge fields that satisfy Gauss’s law. We show that Wilson fermions, already in the minimal one-flavor theory, naturally enable topological regimes with nonzero Chern numbers, and that the two-flavor extension at finite chemical potential further enriches the accessible topological structure. We develop gauge-invariant diagnostics of topological response, including many-body Chern numbers and current correlators that remain robust probes at weak coupling. Finally, through extensive exact diagonalization calculations across both flavor settings, we characterize the spectrum, correlators, and topological invariants, providing a concrete foundation for near-term quantum simulations of topological phases in lattice field theories. The implications of this work for quantum simulations of lattice field theory are analyzed in a joint submission [S. Bharadwaj et al., Companion letter, Phys. Rev. Lett. 137, 191604 (2026).].

Searches for QCD axions with masses in the $\mathrm{n}\mathrm{eV}/c^2$ mass range are strongly motivated by new physics at the grand unified theory (GUT) scale and by well-motivated preinflationary axion symmetry breaking scales. This parameter space is challenging to probe due to the small axion-photon couplings, which typically require large, high-field magnets with substantial stored energy. In this paper, we propose a new experimental geometry based on a narrow-bore, segmented solenoid that optimizes the collection of the axion-induced signal using LC resonators outside the high-field region of the magnet bore. This alternative optimization significantly reduces the required stored magnetic energy while preserving sensitivity, thus enabling a near-term experiment in the 30–200 MHz ($120-830\mathrm{n}\mathrm{eV}/c^2$) range, with a cost-effective, staged scaling to a GUT-scale experiment in the 100 kHz–30 MHz ($0.4-120\mathrm{n}\mathrm{eV}/c^2$) range.

Using an $e^{+}{e}^{-}$ sample of $20.3{\mathrm{fb}}^{-1}$ collected at a center-of-mass energy $\sqrt{s}=3.773\mathrm{GeV}$ with the BESIII detector, we report measurements of several four-body hadronic decays of $D$ mesons. All studied decay modes are dominated by Cabibbo-favored amplitudes. The absolute branching fractions are determined to be $\mathcal{B}(D^0\to K_S^0{K}_S^0{K}_S^0{\pi }^0)=({7.8}_{-2.0}^{+2.3}\pm 1.5)\times {10}^{-5}$, $\mathcal{B}(D^0\to K_S^0{K}^{+}{K}^{-}{\pi }^0)=({18.4}_{-2.5}^{+2.6}\pm 2.4)\times {10}^{-5}$, $\mathcal{B}(D^0\to K_S^0{K}_S^0{K}^{-}{\pi }^{+})=({12.9}_{-1.6}^{+1.7}\pm 1.3)\times {10}^{-5}$, $\mathcal{B}(D^0\to K_S^0{K}_S^0{K}^{+}{\pi }^{-})=({5.7}_{-1.1}^{+1.2}\pm 1.0)\times {10}^{-5}$, $\mathcal{B}(D^0\to K^{+}{K}^{-}{K}^{-}{\pi }^{+})=({17.4}_{-1.7}^{+1.8}\pm 2.2)\times {10}^{-5}$, $\mathcal{B}(D^{+}\to K_S^0{K}_S^0{K}_S^0{\pi }^{+})=({6.0}_{-1.7}^{+2.1}\pm 1.6)\times {10}^{-5}$, and $\mathcal{B}(D^{+}\to K_S^0{K}^{+}{K}^{-}{\pi }^{+})=({13.8}_{-2.2}^{+2.4}\pm 2.5)\times {10}^{-5}$. Furthermore, significant $\varphi$ signals are found in the decay channels involving a $K^{+}{K}^{-}$ pair, and their fractions are determined as $\mathcal{B}(D^0\to \varphi K_S^0{\pi }^0)/\mathcal{B}(D^0\to K_S^0{K}^{+}{K}^{-}{\pi }^0)=(61_{-14}^{+15}\pm 10)\%$, $\mathcal{B}(D^0\to \varphi K^{-}{\pi }^{+})/\mathcal{B}(D^0\to K^{+}{K}^{-}{K}^{-}{\pi }^{+})=(71_{-10}^{+10}\pm 13)\%$, and $\mathcal{B}(D^{+}\to \varphi K_S^0{\pi }^{+})/\mathcal{B}(D^{+}\to K_S^0{K}^{+}{K}^{-}{\pi }^{+})=(59_{-19}^{+22}\pm 9)\%$. The branching fractions of $D^0\to K_S^0{K}_S^0{K}_S^0{\pi }^0$, $D^0\to K_S^0{K}^{+}{K}^{-}{\pi }^0$, and $D^{+}\to K_S^0{K}_S^0{K}_S^0{\pi }^{+}$ are measured for the first time, and those of $D^0\to K_S^0{K}_S^0{K}^{-}{\pi }^{+}$, $D^0\to K_S^0{K}_S^0{K}^{+}{\pi }^{-}$, $D^0\to K^{+}{K}^{-}{K}^{-}{\pi }^{+}$, $D^0\to \varphi K^{-}{\pi }^{+}$, and $D^{+}\to K_S^0{K}^{+}{K}^{-}{\pi }^{+}$ are measured with improved precision. The first uncertainties are statistical and the second are systematic.

We consider the entropic force in matrix theory. We find the gravity in bulk can be emergent from the entropic force.

Polymer quantization program applied in loop quantum gravity/cosmology leads to nonseparable Hilbert spaces. Commonly, one sidesteps this problem by singling out and working with a separable superselection sector. This is, however, often no longer accessible in more involved models beyond isotropic ones. In an alternative approach, one builds a separable Hilbert space as an integral over all available sectors. Here, we test the dynamics following from the latter on the example of a flat isotropic universe admitting a negative cosmological constant and a massless scalar field. There, numerical evolution of (initially) semiclassical states shows that there is no relevant difference in their long-term semiclassicality properties, in comparison to those in a single-sector approach. Further, the older (problem-specific) numerical methods are compared against an application of more common and more efficient standard tools (eigen library).

We construct finite-tension non-Abelian vortex solutions in a renormalizable ($3+1$)-dimensional $SO(3)$ gauge theory Higgsed to the tetrahedral group $A_4$ by a Higgs field in the spin-3 representation. Since the vacuum manifold is $SO(3)/A_4$, the vortices are characterized by the non-Abelian fundamental group ${\pi }_1(SO(3)/A_4)\simeq {\tilde{A}}_4$, the binary tetrahedral group. We obtain explicit axisymmetric vortex solutions carrying holonomies corresponding to the order-two and order-three conjugacy classes of $A_4$, determine their tensions numerically, and show that they exhibit type-I, type-II, and Bogomol’nyi-Prasad-Sommerfield-like behavior depending on the Higgs and gauge boson mass ratios. The vortices are classified by conjugacy classes of ${\tilde{A}}_4$, while their infrared descriptions are labeled by conjugacy classes of $A_4$. We further demonstrate that the smooth finite-tension vortices reduce in the infrared to Gukov-Witten surface operators of the $A_4$ discrete gauge theory, thereby establishing a finite-energy ultraviolet completion of noninvertible defects in a renormalizable gauge-Higgs theory.