We study rare three- and four-body kaon decays as a probe of light vector and axial-vector bosons coupled to nonconserved currents. We find that searches for $K_L\to {\pi }^0{\pi }^0(X\to e^{+}{e}^{-})$ decays constrain the couplings of light $X$ bosons to light quarks to be as small as $\mathcal{O}({10}^{-5})$. The charged-pion modes $K^{+}\to {\pi }^{+}{\pi }^0(X\to e^{+}{e}^{-})$ and $K_L\to {\pi }^{+}{\pi }^{-}(X\to e^{+}{e}^{-})$ provide weaker limits, but constrain complementary combinations of couplings to the $u$, $d$, and $s$ quarks at the level of $\mathcal{O}({10}^{-4})$. Finally, we also find that double emission of $X$ in $K\to \pi XX$ decays can provide yet additional constraints on the parameter space of light $X$ bosons due to a double $(m_K/m_X{)}^2$ enhancement to the rate. For a 17 MeV boson, these limits add to the known tension between spin-1 bosons coupled to vector and axial-vector currents interpretations of the results of the ATOMKI experiment with meson decay data. Finally, we also comment on negative pion capture on hydrogen and deuterium as a source of light particles and discuss the prospects for testing the 17 MeV boson hypothesis.

This study presents a comparative analysis of a light dark matter (DM) scenario in the minimal supersymmetric Standard Model (MSSM), the $Z_3$-symmetric next-to-minimal supersymmetric Standard Model, and the general next-to-minimal supersymmetric Standard Model (GNMSSM), incorporating constraints from DM relic density, the LUX-ZEPLIN 2024 experiment, Higgs data, and the Large Hadron Collider (LHC). The results suggest that, among the three frameworks, only GNMSSM can naturally accommodate light DM with a mass below 100 GeV. As such, the viable supersymmetry candidate is primarily Singlino-like. One key advantage of the GNMSSM is the effective decoupling between interactions that establish the relic density and those that control direct detection, allowing the model to satisfy all current experimental bounds simultaneously. We further explore two characteristic mass hierarchies in the GNMSSM parameter space, each exhibiting distinct phenomenological behaviors. The first hierarchy, $\tilde{S}<\tilde{B}<\tilde{H}$ (Singlino-Bino-Higgsino), involves a relatively light Bino and allows the Higgsino mass parameter, ${\mu }_{\mathrm{tot}}$, to be as low as about 200 GeV, naturally yielding light DM at tens of GeV. The dominant annihilation channels are then ${\tilde{\chi }}_1^0{\tilde{\chi }}_1^0\to A_s{A}_s$ in the $h_1$ scenario and ${\tilde{\chi }}_1^0{\tilde{\chi }}_1^0\to h_s{A}_s$ in the $h_2$ scenario, where $h_s$ and $A_s$ denote singlet-dominated $CP$-even and $CP$-odd Higgs bosons, respectively. The second hierarchy, $\tilde{S}<\tilde{H}<\tilde{B}$, corresponds to a heavy Bino. In this case, although the DM phenomenology remains qualitatively similar, LHC constraints require ${\mu }_{\mathrm{tot}}\gtrsim 900\mathrm{GeV}$, implying a significant degree of fine-tuning in reproducing the $Z$-boson mass.

Recent Belle II data on $B^{+}\to K^{+}{E}_{\mathrm{miss}}$ show an excess consistent with a two-body decay involving a light invisible particle with mass around 2.1 GeV. We present a UV-complete explanation based on a Higgsed $U(1{)}^{\prime }$ gauge symmetry with a light vector boson $Z^{\prime }$ and a vectorlike top partner, which naturally enhances $b\to s$ transitions. While the minimal model can reproduce the required $B\to K^{(*)}{Z}^{\prime }$ rate, it is excluded by LHCb searches for resonant dimuon decays due to unavoidable loop-induced couplings of $Z^{\prime }$ to charged leptons. We show that a minimal extension with an additional light $U(1{)}^{\prime }$-charged singlet fermion allows $Z^{\prime }$ to decay dominantly invisibly, evades existing constraints coming also from dark photon and collider searches as well as Higgs measurements, and can simultaneously account for the Belle II excess and the observed dark matter abundance through resonant thermal freeze-out.

We present a study using the distillation method to analyze the spectra of nucleon, nucleon-pion, and nucleon-pion-pion states in the positive-parity sector, as well as nucleon and nucleon-pion states in the negative-parity sector. The study uses seven domain-wall fermion ensembles with varying pion masses ($m_{\pi }=139–279\mathrm{MeV}$), lattice spacings ($a^{-1}=1.730\mathrm{GeV}$ and $a^{-1}=2.359\mathrm{GeV}$) and volumes ($m_{\pi }L=3.8–7.5$). To address the large number of contractions in this project, we implemented an algorithm to automate the contraction of nucleon-pion correlation functions that contain an arbitrary number of pions. In the positive-parity sector, we extrapolate the nucleon mass to the physical point. This study demonstrates the effectiveness of the distillation method for baryonic quantities with a focus on multihadronic states and establishes a foundation for future work.

A rigorous analysis is presented for the entanglement spectrum of quantum many-body states possessing a higher-form group-representation symmetry generated by topological Wilson loops, which is generally noninvertible. A general framework based on elementary algebraic topology and category theory is developed to determine the block structure of reduced density matrices for arbitrary bipartite manifolds on which the states are defined. Within this framework, we scrutinize the impact of topology on the entanglement structure for low-dimensional manifolds, including especially the torus, the Klein bottle, and lens spaces. Unlike in the case of 0-form symmetries, the reduced density matrix fragments into area-law-order blocks. By further incorporating gauge invariance, we refine our framework to determine the entanglement structure for topological gauge theories in arbitrary dimensions. In particular, in two dimensions, it is shown for the Kitaev quantum double model that not only the topological entanglement entropy can be reproduced, but also the Li-Haldane conjecture concerning the full entanglement spectrum holds exactly. It demonstrates that the block size of the density matrix corresponds to the number of ways to fuse anyons in the split manifold, and that the degeneracy of the entanglement spectrum is given by the product of the quantum dimensions of all anyons connecting the two manifolds and area-law entanglement spectrum fragmentations.

Motivated by the recently reported resonant structure $X(2300)$, a strong candidate for a fully strange tetraquark with positive parity, we perform a systematic study of fully strange tetra- and pentaquark systems within a chiral quark model. Low-lying $S$-wave configurations of the $ss\overline{s}\overline{s}$ and $ssss\overline{s}$ systems are investigated using the Gaussian expansion method combined with the complex scaling method, which allow for a unified treatment of bound, resonant, and scattering states. For tetraquarks, all possible configurations: meson-meson, diquark-antidiquark, and K-type structures, with complete color bases, are incorporated, while baryon-meson and diquark-diquark-antiquark configurations are considered for pentaquarks. Several weakly bound states and narrow resonances are identified in both sectors. In particular, a compact fully strange tetraquark with $J^{PC}=1^{+-}$ is found near 2.3 GeV, providing a natural interpretation of the $X(2300)$ resonance. Additional exotic states with dominant hidden-color and K-type components are predicted in the mass ranges 1.6–3.1 GeV for tetraquarks and 2.6–3.2 GeV for pentaquarks. The internal structure of these states is analyzed through their sizes, magnetic moments, and wave-function compositions, highlighting the essential role of channel coupling and exotic color configurations. Finally, promising two-body strong decay channels are proposed to facilitate future experimental searches.

Establishing quantum gravity theory remains one of the major challenges in modern physics, as the lack of experimental evidence makes it difficult to explore. In response to this challenge, proposals to test quantum entanglement induced by Newtonian gravity in tabletop experiments have attracted significant attention as a potentially feasible approach far below the Planck energy scale. In this work, we propose a scheme to amplify gravity-induced entanglement between two masses using parametric resonance. Specifically, we consider two parametrically resonant oscillators interacting through Newtonian gravity, each governed by the Mathieu equation. We analyze the logarithmic negativity between two oscillators and investigate the effects of random force noise and linear damping. As a result, we find an exponential growth of gravity-induced entanglement between the oscillators, which reflects the dynamical instability of parametric resonant systems.

Numerical relativity simulations provide a full description of the dynamics of binary systems, including gravitational radiation. The waveforms produced by these simulations have a number of applications in gravitational-wave detection and inference. In this work, we revisit the accuracy of the waveforms produced by the spectral Einstein code. Motivated by the wide range of waveform applications, we propose and explore three accuracy metrics between simulation resolutions: (i) the generalized frequency-weighted mismatch, (ii) the relative amplitude difference, and (iii) the phase difference at different times. We confirm that numerical errors accumulate over the binary evolution, but the error is not intrinsically larger during the latest, more dynamical stages. Studying errors across the parameter space, we identify a positive correlation between both the mismatch and the phase difference with precessing spin, but little correlation with aligned spin or eccentricity. Lastly, amplitude and phases differences are symmetric upon exchanging resolutions across the catalog, suggesting that the dominant source of error is random, rather than something systematic that affects all waveforms similarly.

We study the minimal gravitational portal for a massive spin-2 dark matter candidate $X_{\mu \nu }$ produced during perturbative reheating. The dark sector couples to the visible sector only via gravity, and we analyze two unavoidable channels: (i) inflaton condensate annihilation, $\varphi +\varphi \to X+X$, and (ii) thermal scatterings, $\mathrm{SM}+\mathrm{SM}\to X+X$, both mediated by graviton exchange. Working in the Fierz-Pauli framework for a free massive spin-2 field of mass $m_2$, we derive the graviton-mediated amplitudes and perform a full helicity decomposition of the final state. The relic abundance is obtained analytically in terms of $m_2$ and the reheating temperature $T_{\mathrm{RH}}$. In the light mass regime $m_2\ll m_{\varphi }$ (with $m_{\varphi }$ the inflaton mass during oscillations), production is overwhelmingly dominated by the longitudinal (helicity-0) mode: the $2\to 2$ cross section is parametrically enhanced, scaling as $\sim (m_{\varphi }/m_2{)}^4$, and yields efficient dark matter production despite purely gravitational couplings. Compared to lower-spin cases (spin-0, $1/2$, 1, and $3/2$), massive spin-2 production is substantially more efficient for the same reheating history. Over most of the parameter space the inflaton condensate channel dominates the yield, while the thermal contribution is negligible. Avoiding overproduction typically requires either a relatively low $T_{\mathrm{RH}}$ or a spin-2 mass near threshold, $m_2\lesssim m_{\varphi }$. This places the spin-2 portal on similar footing to other higher spins in reheating scenarios, while emphasizing the central role of the helicity-0 mode and the reheating history in setting the dark matter density.

Foreground masking and incomplete sky coverage complicate cosmic microwave background (CMB) polarization analyses by inducing mode coupling and imperfect E/B separation, with particularly strong impact on searches for primordial $B$ modes. We present SkyReconNet-P, a convolutional neural network for inpainting CMB polarization maps that extends the SkyReconNet framework to jointly reconstruct the polarization $(Q,U)$ maps from partial-sky observations. The method combines regional processing with a hybrid design, utilizing standard convolution and dilated convolution to do a multiscale feature integration. We evaluate performance at both the map and power spectrum level using two masking scenarios: a generated random mask and the Planck 2018 common polarization inpainting mask. For both masking scenarios, SkyReconNet-P reproduces the large-scale morphology of the target maps. In power-spectrum space, we find that the reconstructed $E$ mode spectrum closely tracks the target at low multipoles, while small biases emerge at higher $\ell$. For $B$ mode, the raw reconstructed spectra exhibit a larger multipole-dependent bias, which we mitigate using a simulation-based linear calibration. We show that the calibrated $B$-mode spectrum preserves more information by comparing it with spectrum estimation using pseudo-$C_{\ell }$. Finally, we demonstrate cosmological parameter inference from calibrated reconstructed spectra by fitting $(r,A_{\mathrm{lens}})$ with a Gaussian bandpower likelihood, recovering posteriors consistent with injected parameters across three test ensembles down to $r\sim {10}^{-3}$. These results support inpainting as a complementary route to cut-sky approaches when downstream pipelines can greatly benefit from statistically well-characterized, gap-filled polarization maps.

The merger rate of primordial black hole (PBH) binaries can be used to understand the source population of the merging black hole binaries observable through gravitational waves (GWs) and also to constrain the possible contribution of PBHs to dark matter. In the literature, the PBH merger rate is calculated analytically, assuming that PBH binaries stay in isolation (i.e., are unperturbed) and evolve solely via GW emission during their entire lifetime. However, if some or all of dark matter consists of PBHs, then as cosmic structures grow, PBH binaries and single PBHs fall inside dark matter halos. In those halos, the PBH binaries’ interactions with their environment significantly affect the subsequent evolution of their orbital properties. In this paper, we present a numerical framework that accurately calculates the total PBH merger rate by combining the evolution of isolated binaries outside halos with the dynamics of binaries inside halos. In our work, we have found that the isolated binary channel is suppressed at low redshifts, and dynamical interactions in halos reshape the merger rate evolution with time, accelerating some mergers. At redshifts of $\lesssim 2$ the total merger rate is a factor of $\simeq 50\%$ higher than the results assuming that all PBH binaries effectively stay unperturbed until their merger. Our simulations provide a definitive calculation on the total PBH merger rates, which are currently being probed and constrained from gravitational-wave observations. We make our merger rates publicly available via Zenodo.

Unstable states that live long enough may appear as in(out)going particles in scattering experiments. Yet, the standard QFT approach strictly applies only to fully stable asymptotic states. This is evident when scattering involving unstable particles develops a $t$-channel singularity at specific angles. We employ a finite-time formalism leading to analytic results without the singularity (even in the infinite-time limit), thus solving the problem at a phenomenological level. In turn, the approach also justifies treating long-lived particles, like weakly decaying pions, as stable during strong interactions.

We investigate dilepton production in a thermalized quark-gluon plasma subject to global rotation, in the rigid rotating approximation. We consider a generic process involving quark-antiquark annihilation followed by the emission of a highly energetic virtual photon decaying into a dilepton pair. For this process, we compute the dilepton emission rate from the imaginary part of the photon polarization tensor, at finite temperature and vorticity. Our results show that vorticity induces characteristic modifications in the light dilepton channel, namely, $e^{-}{e}^{+}$ production, where the emission spectrum exhibits a suppression at low transverse mass together with a mild shift of the production threshold. This behavior originates from the role of vorticity as an effective spin-dependent chemical potential that alters the available phase-space distribution for the emission process. In contrast, the ${\mu }^{-}{\mu }^{+}$ channel is more weakly affected by the rotational background, thus remaining dominated by its intrinsic mass threshold. The resulting channel dependence highlights a potential phenomenological handle for disentangling rotational effects in heavy-ion collisions: while light dilepton spectra encode the imprints of vorticity in the infrared sector, the muon channel provides a comparatively robust baseline.

Super-Kamiokande (SK) has observed ${}^8\mathrm{B}$ solar neutrino elastic scattering at recoil electron kinetic energies ($E_{\mathrm{kin}}$) as low as 3.49 MeV to study neutrino flavor conversion within the Sun. At SK-observable energies, these conversions are dominated by the Mikheyev-Smirnov-Wolfenstein effect. An upturn in the electron neutrino survival probability in which vacuum neutrino oscillations become dominant is predicted to occur at lower energies, but radioactive background increases exponentially with decreasing energy. New machine learning approaches provide substantial background reduction below 3.49 MeV such that statistical extraction of solar neutrino interactions becomes feasible. This article presents an analysis of the solar neutrino interaction rate at $E_{\mathrm{kin}}<3.49\mathrm{MeV}$ with the full SK-IV period, using data from a wideband intelligent trigger when available and with a boosted decision tree for event selection. A solar neutrino signal is observed between $2.99\mathrm{MeV}<E_{\mathrm{kin}}<3.49\mathrm{MeV}$ with $2.76\sigma$ significance and a data to unoscillated Monte Carlo ratio of ${0.307}_{-0.111}^{+0.112}$. These additional low-energy data have a negligible effect on the $1\sigma$ intervals of the fits to the solar neutrino energy spectrum but have a noticeable effect on the best fit when using the exponential parametrization.

Complex states of quantum gravity in flat and Anti de Sitter gravity can have features that are inaccessible to classical asymptotic observers. The missing information appears to such observers to be hidden behind a horizon or in a baby universe. Here we use the gravitational path integral to ask whether quantum observables can access the hidden data. We show that generic probes give a universal result and contain no information about the state. However, a probe appropriately fine-tuned to the state can give a large signal because of novel wormhole saddles in the path integral. Thus, in these settings, asymptotic observers cannot easily determine the state of the universe, but can check a proposal for it. Using these fine-tuned probes we show that an asymptotic observer can detect information hidden in a disconnected baby universe. Furthermore we show that the state of a two-boundary black hole can be detected using Lorentzian operators localized on just one of the boundaries.

We establish a relationship between the Davey-Stewartson II (DS II) integrable system in ($2+1$) dimensions and quasiexactly solvable planar interacting Dirac Hamiltonians that exhibit the super-Klein tunneling (SKT) effect. The Dirac interactions are constructed from the real and imaginary parts of breather solutions of the DS II system. In this framework, the SKT effect arises when the energy is tuned to match the constant background of the soliton, while the resulting Dirac Hamiltonians simultaneously support bound states embedded in the continuum. By imposing the SKT boundary conditions, we employ Darboux transformations to construct a general three-parameter family of DS II breather solutions that can be mapped to Dirac Hamiltonians. At the initial soliton time, the corresponding Dirac systems form a massless two-parameter family of Hermitian models with nontrivial electrostatic potentials. As the soliton time evolves, the systems become $\mathcal{P}\mathcal{T}$-symmetric and develop a nontrivial imaginary mass term. Finally, when the soliton time is taken to be imaginary, the construction yields Hermitian Dirac systems that lack time-reversal symmetry. In all cases, we identify the emergence of quasisymmetry transformations that preserve the SKT subspace of states while not commuting with the full Hamiltonian.

We investigate the connection between entanglement entropy and the notion of irreversibility in the renormalization-group flow in the context of a simple theory for which an explicit calculation from first principles is feasible. The change of the entanglement entropy for a spherical entangling surface as its radius grows from zero to infinity corresponds to the flow from the UV to the IR. Through analytical and numerical means, we compute the entanglement entropy for a free massive scalar theory, making use of the method of correlation functions. We deduce a $c$-function in $1+1$ dimensions and an $a$-function in $3+1$ dimensions. Both functions are monotonic and vary continuously between one and zero, which are the expected values for this theory.

We study entanglement entropy of quantum fields in a ($1+1$)-dimensional model of dilaton gravity derived from the four-dimensional Einstein-Hilbert action by dimensional reduction. Scalar matter is coupled to gravity, while the backreaction is included via the Polyakov-Liouville action. This theory exhibits both eternal and evaporating Schwarzschild black hole solutions. The fine-grained entropy in a collapse scenario is investigated by applying the “island rule” via the quantum extremal surface approach. We demonstrate that the fine-grained entropy of the Hawking radiation follows the Page curve, and therefore the evolution of the Hawking radiation is unitary.

From the perspective of quantum information science, we investigate tree-level Bhabha scattering between an incident electron $A$ and a positron B, where $B$ is initially entangled with a spectator electron $C$, which does not participate in the scattering interaction. We find that the QED scattering between $A$ and $B$ can drive the global $ABC$ system into a genuine tripartite entangled (GTE) state. Using four canonical tripartite entanglement metrics, we systematically characterize and quantify the GTE of the composite system, and demonstrate that the scattering momentum of the $A\text{−}B$ pair and the initial $B\text{−}C$ entanglement are the key resources governing GTE generation. We further analyze the monogamy of quantum correlations, which imposes fundamental constraints on the shareability of quantum resources in multipartite systems. Specifically, we systematically study the monogamy relations for the squared entanglement of formation and squared quantum discord in our scattering model, and find that monogamy constraints are markedly relaxed in the nonrelativistic regime, enabling enhanced shareability of quantum correlations across the three particles. This work uncovers novel quantum correlation properties of fundamental QED scattering processes, and provides direct theoretical guidance for the development of QED-based quantum information processing protocols.