Scalar ultralight dark matter (ULDM) is uniquely accessible to tabletop experiments such as clocks and interferometers, and its search has been the focus of a vast experimental effort. However, the scalar ULDM mass is not protected from radiative corrections, and the entirety of the parameter space within reach of experiments suffers from a severe naturalness problem. In this paper, we propose a new twin mechanism that protects the mass of the scalar ULDM. Our scalar ULDM is a pseudo-Nambu-Goldstone boson with quadratic couplings to the standard model (SM) and to a twin copy of the SM, with a mirror ${\mathbb{Z}}_2$ symmetry exchanging each SM particle with its twin. Due to the mirror symmetry, the leading-order mass correction is quadratic in the (tiny) coupling while the linear order is canceled. This opens up vast regions of parameter space for natural quadratically coupled ultralight dark matter, within the sensitivity of existing and future experiments.

We investigate the phase structure of the ($3+1$)-dimensional strong coupling two-color QCD at zero temperature ($T=0$) with finite chemical potential using the tensor renormalization group method. The chiral and diquark condensates and the quark number density are evaluated as a function of the chemical potential. We further determine the critical exponents associated with the diquark condensate, which suggest consistency with the predictions of mean-field theory.

Using a variety of experimental results and lattice QCD calculations of $\pi \pi$ scattering lengths, while employing dispersive representations of the amplitude based on Roy equations, we compute the subthreshold parameters of this process. We use Monte Carlo sampling to numerically model the probability distribution of the results based on all uncertainties in the inputs. We also investigate the dependence of the results on a theoretical correlation between the $\pi \pi$ scattering lengths $a_0^0$ and $a_0^2$, which was previously established in the framework of two-flavor $\chi \mathrm{PT}$.

A systematic investigation of $S$-wave triply heavy tetraquark systems with quark content $\overline{b}c\overline{q}c$ and $\overline{c}b\overline{q}b$ ($q=u$, $d$, $s$), spin-parity quantum numbers $J^P=0^{+}$, $1^{+}$, $2^{+}$, and isospin $I=0,\frac{1}{2}$ is carried out within the constituent quark model framework. The four-body bound and resonance states are determined by solving the Schrödinger equation employing the high-precision and efficient Gaussian expansion method in conjunction with the powerful complex scaling method. Besides, a comprehensive coupled-channel analysis of the $S$-wave tetraquark systems is performed, taking into account meson-meson, diquark-antidiquark, and K-type configurations, as well as all allowed color structures. Several narrow resonant states are identified in each $I(J^P)$ channel. In particular, resonances for the $\overline{b}c\overline{q}c$ system are found in the mass range of 8.87–9.36 GeV, while those for the $\overline{c}b\overline{q}b$ system lie between 12.13–12.45 GeV. Most of the predicted resonances are compact tetraquark states with sizes smaller than 1.0 fm, although four states exhibit more extended structures with sizes around 1.3 fm, suggesting a more loosely bound nature. Magnetic moments and dominant wave function components of these exotic states are also analyzed. The results indicate that K-type configurations play a major role in the structure of the observed resonances. Finally, possible strong decay channels (golden modes) for these states are theoretically proposed.

We demonstrate that nuclear magnetic resonance based searches for dark matter (DM) have intrinsic and powerful sensitivity to dark photons and the axion-photon coupling. The reason is conceptually straightforward. An instrument such as CASPEr-Gradient begins with a large sample of nuclear spins polarized in a background magnetic field. In the presence of axion DM coupled to nucleons, the spin ensemble feels an effective magnetic field $\mathbf{B}\propto \nabla a$ that tilts the spins, generating a potentially observable precession. If the magnetic field is real rather than effective, the system responds identically. A real field can be generated by a kinetically mixed dark photon within the shielded region the sample is placed or an axion coupled to photons through its interaction with the background magnetic field. We show that all three signals are detectable and distinguishable. If CASPEr-Gradient were to reach the QCD axion prediction of the axion-nucleon coupling, it would simultaneously be sensitive to kinetic mixings of $\epsilon \simeq 3\times {10}^{-16}$ and axion-photon couplings of $g_{a\gamma \gamma }\simeq 2\times {10}^{-16}{\mathrm{GeV}}^{-1}$ for $m\simeq 1\mu \mathrm{eV}$. Our analysis demonstrates that CASPEr-Gradient has the tantalizing possibility of simultaneously measuring two separate couplings of axion dark matter, thereby providing a unique window into the axion’s UV completion.

Inspired by the BESIII newest observation of an axial-vector particle $X(2300)$ in the $\psi (3686)\to \varphi \eta {\eta }^{\prime }$ process [M. Ablikim et al. (BESIII Collaboration), Phys. Rev. Lett. 134, 191901 (2025)], we simulate its production in $e^{+}{e}^{-}$ collisions at $\sqrt{s}=4.95\mathrm{GeV}$ using the parton and hadron cascade model PACIAE 4.0. In this model, the final partonic state (FPS) and the final hadronic state (FHS) are simulated and recorded sequentially. While previous interpretations have described the $X(2300)$ as an excited strangeonium state or an $ss\overline{s}\overline{s}$ tetraquark state, it is noted that the $U(1)$ anomaly coupling permits nonstrange quarks to couple to a vector $s\overline{s}$ component via soft-gluon interactions. This motivates us to propose, for the first time, that the $X(2300)$ could also be a $q\overline{q}s\overline{s}$ ($q=u/d$) state. Furthermore, we suggest another novel possibility that the $X(2300)$ may be a hadro-strangeonium state, i.e., a bound system of a strangeonium and a light hadron. The excited strangeonium candidate is formed by coalescing an $s\overline{s}$ quark pair in the FPS with the quantum statistical mechanics inspired dynamically constrained phase-space coalescence (DCPC) model. The tetraquark candidates of $q\overline{q}s\overline{s}$ and $ss\overline{s}\overline{s}$ are similarly produced by coalescing four constituent quarks in the FPS. In contrast, a hadro-strangeonium candidate emerges from the recombination of the constituent mesons $\varphi$ and ${\eta }^{\prime }/\eta$ in the FHS. We then calculate the $X(2300)$’s orbital angular momentum quantum number in its rest frame and perform the spectral classification for each of the above candidates. Given its quantum numbers $J^{PC}=1^{+-}$, the $X(2300)$ is identified as a $P$-wave $s\overline{s}$, an $S$-wave $q\overline{q}s\overline{s}/ss\overline{s}\overline{s}$ or an $S$-wave $\varphi {\eta }^{\prime }/\varphi \eta$ candidate. For the first time, we estimate the production rates for these configurations. The $P$-wave $s\overline{s}$ and $S$-wave $q\overline{q}s\overline{s}$ states are produced at rates on the order of ${10}^{-5}$, whereas the $S$-wave $ss\overline{s}\overline{s}$ and $\varphi {\eta }^{\prime }/\varphi \eta$ states appear at rates on the order of ${10}^{-6}$. Moreover, significant discrepancies are observed in the rapidity distributions and the transverse momentum spectra among the different candidates. These discrepancies could be served as valuable criteria for deciphering the nature of the $X(2300)$.

The holographic Green’s function becomes ambiguous, taking the indeterminate form “$0/0$,” at an infinite set of special frequencies and momenta known as “pole-skipping points.” In this work, we propose that these pole-skipping points can be used to reconstruct both the interior and exterior geometry of a static, planar-symmetric black hole in the bulk. The entire reconstruction procedure is fully analytical and only involves solving a system of linear equations. We demonstrate its effectiveness across various backgrounds, including the Bañados-Teitelboim-Zanelli black hole, its $T\overline{T}$-deformed counterparts, as well as geometries with Lifshitz scaling and hyperscaling-violation. Within this framework, other geometric quantities, such as the vacuum Einstein equations, can also be reinterpreted directly in terms of pole-skipping data. Moreover, our approach reveals a hidden algebraic structure governing the pole-skipping points of Klein-Gordon equations of the form $({\nabla }^2+V(r))\varphi (r)=0$: only a subset of these points is independent, while the remainder is constrained by an equal number of homogeneous polynomial identities in the pole-skipping momenta. These identities are universal, as confirmed by their validity across a broad class of bulk geometries with varying dimensionality, boundary asymptotics, and perturbation modes.

We study fermionic instantons of the Gross-Neveu and the Gross-Neveu-Yukawa models. We derive new solutions for both models and examine the corresponding actions at the fixed points. We further map the solutions on to the sphere and discuss the relation to the Hubbard-Stratonovich approach. Close to the fixed points we compare and identify the results with those obtained in the large $N$ computation.

We show that the Unruh response can be interferometrically suppressed or restored in a single Unruh-DeWitt detector whose center of mass is prepared in a coherent superposition of two uniformly accelerated worldlines. The two paths remain physically disjoint; the detector is read out in a path-erasing basis so that no which-path information is revealed. If the detector’s energy gap is path dependent during the interaction, the branch amplitudes for first-order excitation become operationally indistinguishable and, therefore, add coherently. With appropriate tuning—matching the gap-to-acceleration ratios of the two branches and choosing a single relative phase—the conditional first-order excitation amplitude cancels, while reversing the phase restores the response. We derive these conditions in two complementary formalisms and interpret the mechanism as a relativistic analog of electromagnetically induced transparency, which we term worldline-induced transparency. We also treat finite switching times explicitly and quantify how imperfect matching produces a residual signal, yielding a tolerance window rather than an idealized infinitely sharp condition.

Scale-dependent gravity is an extension of general relativity in which the Newton and cosmological constants may vary slightly with the energy scale due to remnant low-energy quantum effects. A fundamental feature of this approach is the scale-setting procedure. In a previous work, a covariant expression for the scale, consistent with conservation laws, was established. Here, we apply the full Will-Nordtvedt version of the parametrized post-Newtonian (PPN) formalism to this framework, assuming that the constants can be expressed as a power series in the scale. We find that a new potential arises at the first post-Newtonian order, which is absent from the standard PPN formalism. This potential modifies the definitions of pressure and internal energy but does not affect center-of-mass orbits and is, therefore, not constrained by Solar System tests.

We revisit the theoretical modeling and simulation of a Gaussian stochastic gravitational wave background (SGWB) signal in a pulsar timing array (PTA). We show that the correlation between Fourier components of pulsar timing residuals can be expressed using transfer functions; that are indicative of characteristic temporal correlations in a SGWB signal observed in a finite time window. These transfer functions, when convolved with the SGWB power spectrum and spatial correlation (Hellings and Downs curve), describe the variances and correlations of the pulsar timing residuals’ Fourier coefficients. The convolutions are the exact frequency- and Fourier-domain representations of the time-domain covariance function. We derive explicit forms for the transfer functions for unpolarized and circularly polarized SGWB signals. We validate our results by comparing Gaussian theoretical expectation values with standard simulations based on point sources and our own covariance-matrix-based approach. The unified frequency- and Fourier-domain formalism provides a robust foundation for future PTA precision analyses and highlights the importance of temporal correlations in interpreting GW signals.

Neutrino self-interactions ($\nu \mathrm{SI}$) mediated by light bosonic particles can produce characteristic spectral dips in astrophysical neutrino fluxes, thereby altering the expected energy spectrum. The high-energy astrophysical neutrino spectrum has been extensively used to probe $\nu \mathrm{SI}$ models through these distinctive features. The recent detection of the ultrahigh-energy event KM3-230213A presents a new opportunity to explore $\nu \mathrm{SI}$ phenomenology at extreme energies. In this work, we investigate two implications of this observation, assuming the event originates from a diffuse power-law spectrum. First, we find that $\nu \mathrm{SI}$-induced spectral distortions can mildly alleviate the tension between the KM3-230213A detection and the previous nonobservation of PeV-scale neutrinos in IceCube data. Second, we derive the strongest constraints on the $\tau$-flavored $\nu \mathrm{SI}$ coupling strength for mediator masses around 100 MeV. Our analysis shows that neutrino telescopes can surpass existing collider bounds in this mass range. In the near future, IceCube-Gen2 is expected to significantly enhance $\nu \mathrm{SI}$ sensitivity, including regions relevant to alleviating the Hubble and neutrino mass tensions.

Astrometric observations can, in principle, be used to detect gravitational waves. In this paper, we give a practical overview of the gravitational wave effects which can be expected specifically in small-field astrometric data. Particular emphasis is placed on the differential effect between pairs of sources within a finite field of view. We also present several general findings that are not restricted to the small-field case. A detailed theoretical derivation of the general astrometric effect of a plane gravitational wave is provided. Numerical simulations, which underline our theoretical findings, are presented. We find that small-field missions suffer from significant detrimental properties, largely because their relatively small fields only allow the measurement of small differential effects which can be expected to be almost totally absorbed by standard plate calibrations.

Important scientific discoveries should be backed by high statistical significance. In the 2030s, multiple space-based gravitational wave detectors are expected to operate. While many works aim to achieve quick and reliable detection and parameter estimation of millihertz gravitational wave sources, dedicated studies are lacking to assess the significance of space-based detectors. In this work, we propose a framework to assess the statistical significance of massive black hole binary (MBHB) detections with space-based gravitational wave detectors. We apply this algorithm to simulated data with Gaussian stationary noise and the complex LDC-2a dataset to measure the false alarm rate and significance of MBHB signals. We also analyze factors affecting the significance of MBHBs and design a method to mitigate multisource confusion interference. In Gaussian noise conditions, MBHBs with a signal-to-noise ratio of about 7 can achieve $3\sigma$ significance, and those with a signal-to-noise ratio of about 8 achieve $4\sigma$. Our analysis demonstrates that all MBHB signals in the LDC-2a dataset have a significance exceeding $4.62\sigma$.

We present the public release of the low-frequency atlas of continuous gravitational waves, covering signals with frequencies from 20 Hz to 200 Hz and frequency derivatives from $-5\times {10}^{-11}$ to $5\times {10}^{-11}\mathrm{Hz}/\mathrm{s}$. Compared to the previous atlas releases, this version demonstrates significant improvements in sensitivity and sky resolution. In the most sensitive region, even the worst-case upper limits on gravitational wave strain are below ${10}^{-25}$. The atlas data are being released ahead of the completion of the full follow-up analysis.

We show that mono-energetic axions are produced in abundance through nuclear de-excitations in nearby galaxies such as M87, which is the central galaxy of the Virgo cluster, and the starburst galaxy M82. If the axion couples to both nucleons and photons and is ultralight, then monochromatic hard x-ray signatures are induced by the subsequent axion-to-photon conversion in the magnetic fields permeating these systems. We search for evidence of such signals using NuSTAR data, focusing specifically on the ${}^{57}\mathrm{Fe}$ de-excitation line at 14.4 keV, and we catalog other potentially relevant nuclear lines. We find no evidence for axions from M87 or M82 and set stringent constraints on the combined axion-nucleon and axion-photon coupling at the level of $|g_{ann}\times g_{a\gamma \gamma }|\lesssim 1.1\times {10}^{-22}{\mathrm{GeV}}^{-1}$ in the limit $m_a\lesssim {10}^{-10}\mathrm{eV}$ at 95% confidence.

Nonglobal logarithms are low energy correlations between the substructure of a jet and the event in which it is immersed. We study the leading nonglobal logarithms that arise from soft quark-antiquark emission and calculate their coefficient as a series in the jet radius, $R$, in arbitrary processes. We calculate the exact coefficient through quadratic order in $R$, and show that this truncation is within 5% of the complete result for radii up to $R=1$. These quark flavor-dependent nonglobal logarithms are also responsible for the infrared unsafety of a naïve definition of jet flavor that is simply the net sum of quark flavors in the jet of interest. We propose a small modification of this naïve jet flavor that we call subtractive jet flavor in which the problematic soft logarithms are explicitly subtracted. We further demonstrate how our analytic results can be interfaced with automated numerical fixed-order codes to extract subtractive jet flavor cross sections.

The recent observation of the X(2600) resonance by the BESIII Collaboration has motivated a renewed interest in the spectroscopy of light mesons, particularly pseudotensor states. However, a significant theoretical gap exists in the poorly explored spectrum of isoscalar pseudotensor mesons, where several predicted radial excitations remain unobserved. To address this, we investigate the production of four such states [${\eta }_2(4D)$, ${\eta }_2^{\prime }(2D)$, ${\eta }_2^{\prime }(3D)$, and ${\eta }_2^{\prime }(4D)$] employing an effective Lagrangian approach combined with Regge trajectory phenomenology to describe the high-energy behavior of the reactions. Our calculations reveal a distinct production selectivity: the ${\eta }_2(4D)$ state is more prominent in pion induced (${\pi }^{-}p\to {\eta }_{2}n$) reactions, whereas the ${\eta }_2^{\prime }(2D,3D,4D)$ states are preferentially produced in kaon induced ($K^{-}p\to {\eta }_2\mathrm{\Lambda }$) processes. Moreover, the total cross sections for these states exhibit characteristic peaks at specific beam momenta, providing clear kinematic windows for their discovery. This study provides the first comprehensive theoretical predictions for the production cross sections of these predicted mesons, offering crucial guidance for future experimental searches.