Nonradial oscillation modes of a neutron star possess valuable information about its internal structure and nuclear physics. Starting from the quadrupolar order, such modes under general relativity are known as quasi-normal modes since they dissipate energy through gravitational radiation and their frequencies are complex. The stability of these modes is governed by the sign of the imaginary part of the frequency, which determines whether the mode would decay or grow over time. In this paper, we develop a fully consistent framework in general relativity to study quasi-normal modes of neutron stars with anisotropic pressure, whose motivation includes strong internal magnetic fields and nonvanishing shear or viscosity. We employ parametrized models for the anisotropy, with a specific form under perturbation that is consistent with previous studies under the Cowling approximation, and solve the perturbed Einstein field equations numerically. The assumed form of the perturbed anisotropy can be easily extended to more general cases. We find that, unlike the case for isotropic neutron stars, the imaginary parts of some of the pressure ($p$-)modes flip signs as the degree of anisotropy deviates from zero, depicting a transition from stable modes to unstable modes. This finding indicates that some anisotropic neutron star models are unstable, potentially restricting the form of sustained anisotropy.

Quasiperiodic eruptions (QPEs) are intense repeating soft x-ray bursts with recurrence times about a few hours to a few weeks from galactic nuclei. Though the debates on the origin of QPEs have not completely settled down, more and more analyses favor the interpretation that QPEs are the result of collisions between a stellar mass object (a stellar mass black hole or a main sequence star) and an accretion disk around a supermassive black hole (SMBH) in galactic nuclei. If this interpretation is correct, QPEs will be invaluable in probing the orbits of stellar mass objects in the vicinity of SMBHs, and further inferring the formation of extreme mass ratio inspirals (EMRIs), one of the major targets of spaceborne gravitational wave missions. In this work, we extended the EMRI orbital analysis in paper I [C. Zhou et al., Probing orbits of stellar mass objects deep in galactic nuclei with quasi-periodic eruptions, Phys. Rev. D 109, 103031 (2024)] to all the known QPE sources with more than 6 flares observed. Among all the analyzed 5 QPE sources, two distinct EMRI populations are identified: 4 EMRIs are of low orbital eccentricity (consistent with 0) which should be born in the wet EMRI formation channel, and 1 mildly eccentric EMRI (with $e=0.25_{-0.20}^{+0.18}$ at $2\text{−}\sigma$ confidence level) is consistent with the predictions of both the dry loss-cone formation channel and the Hills mechanism.

Neutron stars (NSs) can capture dark matter (DM) particles because of their deep gravitational potential and high density. The accumulated DM can affect the properties of NSs. In this work we use a general relativistic two-fluid formalism to solve the structure of DM-admixed NSs (DANSs) and the surrounding spacetime. Specifically, we pay attention to the situation where those DANSs possess DM halos. Due to the gravitational effect of the DM halo, the pulse profile of an x-ray pulsar is changed. Our study finds a universal relation between the peak flux deviation of the pulse profile and $M_{\mathrm{halo}}/R_{\mathrm{BM}}$, which is the ratio of the DM halo mass, $M_{\mathrm{halo}}$, to the baryonic matter (BM) core radius, $R_{\mathrm{BM}}$. Our results show that, when $M_{\mathrm{halo}}/R_{\mathrm{BM}}=0.292$ and the DM particle mass $m_f=0.3\mathrm{GeV}$, the maximum deviation of the profile can be larger than 100%, which has implications in x-ray pulsar observation.

This work for the first time addresses the feasibility of measuring millihertz gravitational waves (mHz GWs) with a storage ring-based detector. While this overall challenge consists of several partial problems, here we focus solely on quantifying design limitations imposed by the kinetic energy and radiated power of circulating ions at relativistic velocities. We propose an experiment based on the measurement of the time-of-flight signal of an ion chain. One of the dominant noise sources inherent to the measurement principle for such a GW detector is the shot noise of the emitted synchrotron radiation. We compute the noise amplitude of arrival time signals obtained by analytical estimates and simulations of ions with different masses and velocities circulating in a storage ring with the circumference of the Large Hadron Collider. Thereby, we show that our experiment design could reduce the noise amplitude due to the synchrotron radiation in the frequency range ${10}^{-4}–{10}^{-2}\mathrm{Hz}$ to one or two orders of magnitude below the expected GW signals from of astrophysical sources, such as supermassive binary black holes or extreme mass-ratio inspirals. Other key requirements for building a working storage ring-based GW detector include the generation and acceleration of heavy ion chains with the required energy resolution, their injection and continued storage, as well as the detection method to be used for the determination of the particle arrival time. However, these are not the focus of the work presented here, in which we instead concentrate on the definition of a working principle in terms of ion type, kinetic energy, and ring design, which will later serve as a starting point when addressing a more complete experimental setup.

We study the renormalization flow of generic actions that depend on the invariants of the field strength tensor of an Abelian gauge field. While the Maxwell action defines a Gaussian fixed point, we search for further non-Gaussian fixed points or rather fixed functions, i.e., globally existing Lagrangians of the invariants. Using standard small-field expansion techniques for the resulting functional flow equation, a large number of fixed points is obtained, which—in analogy to recent findings for a shift-symmetric scalar field—we consider as approximation artifacts. For the construction of a globally existing fixed function, we pay attention to the use of proper initial conditions. Parametrizing the latter by the photon anomalous dimension, both the coefficients of the weak-field expansion are fully determined and those of the large-field expansion can be matched such that a global fixed function can be constructed for magnetic fields. The anomalous dimension also governs the strong-field limit. Our results provide evidence for the existence of a continuum of non-Gaussian fixed points parametrized by a small positive anomalous dimension below a critical value. We discuss the implications of this result within various scenarios with and without additional matter. For the strong-field limit of the 1PI QED effective action, where the anomalous dimension is determined by electronic fluctuations, our result suggests the existence of a singularity free strong-field limit, circumventing the standard conclusions connected to the perturbative Landau pole.

The identification of prospective scenarios for observing quantum vacuum signals in high-intensity laser experiments requires both accurate theoretical predictions and the exploration of high-dimensional parameter spaces. Numerical simulations address the first requirement, while optimization provides an efficient solution for the second one. In the present work, we put forward Bayesian optimization as a new and powerful means to optimize photonic quantum vacuum signals. We demonstrate its great potential on the example of the well-studied case of two-beam collisions. Apart from providing an ideal benchmark case, this immediately gives new physics results. Namely, Bayesian optimization allows us to find the optimal waist sizes for beams with elliptic cross sections, and to identify the specific physical process leading to a discernible signal in a coherent harmonic focusing configuration scenario.

We analyze the quasiparton distributions of the lightest ${\eta }^{\prime }$ meson in massive two-dimensional quantum electrodynamics (QED2) by exact diagonalization. The Hamiltonian and boost operators are mapped onto spin qubits in a spatial lattice with open boundary conditions. The lowest excited state in the exact diagonalization is shown to interpolate continuously between an anomalous ${\eta }^{\prime }$ state at strong coupling, and a nonanomalous heavy meson at weak coupling, with a cusp at the critical point. The boosted ${\eta }^{\prime }$ state follows relativistic kinematics but with large deviations in the luminal limit. The spatial quasiparton distribution function and amplitude for the ${\eta }^{\prime }$ state are computed numerically for increasing rapidity both at strong and weak coupling, and compared to the exact light front results. The numerical results from the boosted form of the spatial parton distributions, compare fairly with the inverse Fourier transformation of the luminal parton distributions, derived in the lowest Fock space approximation. Our analysis points out some of the limitations facing the current lattice program for the parton distributions.

We discuss the exclusive lepton flavor violating (LFV) decays modes based on $b\to d{\ell }_i{\ell }_j$ and $b\to s{\ell }_i{\ell }_j$ by considering the ground state mesons and baryons. After spelling out the expressions for such decay rates in a low energy effective theory which includes generic contributions arising from physics beyond the Standard Model, we show that the experimental bounds on meson decays can be used to bound the corresponding modes involving baryons. We find, for example, $\mathcal{B}({\mathrm{\Lambda }}_b\to \mathrm{\Lambda }\mu \tau )\lesssim 4\times {10}^{-5}$. We also consider two specific models and constrain the relevant LFV couplings by using the low energy observables. In the first model, we assume the Higgs mediated LFV and find the resulting decay rates to be too small to be experimentally detectable. We also emphasize that the regions favored by the bounds $\mathcal{B}(h\to \mu \tau {)}^{\text{Atlas}}$ and $\mathcal{B}(h\to e\tau {)}^{\text{Atlas}}$ are not compatible with $\mathcal{B}(\mu \to e\gamma {)}^{\mathrm{MEG}}$ to $1\sigma$. In the second model, we assume LFV mediated by a heavy $Z^{\prime }$ boson and find that the corresponding $b$-hadron branching fractions can be $\mathcal{O}({10}^{-6})$, thus possibly within experimental reach at LHCb and Belle II.

Long-standing anomalous experimental results from short-baseline neutrino experiments have persisted for decades. These results, when interpreted with one or more light sterile neutrinos, are inconsistent with numerous null results experimentally. However, if the sterile neutrino decays en route to the detector, this can mimic ${\nu }_{\mu }\to {\nu }_e$ oscillation signals while avoiding many of these external constraints. We revisit this solution to the MiniBooNE and LSND puzzles in view of new data from the MicroBooNE experiment at Fermilab. Using MicroBooNE’s liquid-argon time-projection chamber search for an excess of ${\nu }_e$ in the Booster beam, we derive new limits in two models’ parameter spaces of interest; where the sterile neutrino decays (I) via mixing with the active neutrinos, or (II) via higher-dimensional operators. We also provide an updated, comprehensive fit to the MiniBooNE neutrino- and antineutrino-beam data, including appearance (${\nu }_e$) and disappearance (${\nu }_{\mu }$) channels. Despite alleviating the tension with muon neutrino disappearance experiments, we find that the latest MicroBooNE analysis rules out the decaying sterile neutrino solution in a large portion of the parameter space at more than 99% CL.

We provide the first extensive, numerical study of the nontrivial problem of mixing between flavor-singlet composite states emerging in strongly coupled lattice field theories with matter field content consisting of fermions transforming in different representations of the gauge group. The theory of interest is the minimal candidate for a composite Higgs model that also accommodates a mechanism for top partial compositeness: the $Sp(4)$ gauge theory coupled to two (Dirac) fermions transforming as the fundamental and three as the two-index antisymmetric representation of the gauge group, respectively. We apply an admixture of APE smearing and Wuppertal smearings, as well as the generalized eigenvalue problem approach, to two-point functions involving flavor-singlet mesons, for ensembles having time extent longer than the space extent. We demonstrate that, in the region of lattice parameter space accessible to this study, both masses and mixing angles can be measured effectively, despite the presence of (numerically noisy) contributions from disconnected diagrams.

When a hadron is probed at high energy, a nontrivial quantum entanglement entropy inside the hadron emerges due to the lack of complete information about the hadron wave function extracted from this measurement. In the high-energy limit, the hadron becomes a maximally entangled state, with a linear dependence of entanglement entropy on rapidity, as has been found in a recent analysis based on parton description. In this paper, we use an effective conformal field theoretic description of hadrons on the light cone to show that the linear dependence of the entanglement entropy on rapidity found in parton description is a general consequence of approximate conformal invariance and does not depend on the assumption of weak coupling. Our result also provides further evidence for a duality between the parton and string descriptions of hadrons.

We investigate the doubly bottom state $T_{bb}^{-}$ composed of two bottom mesons with $J^P=1^{+}$. The potentials are obtained using the one-boson exchange model. With the heavy quark flavor symmetry, all the parameters in the model are determined by fitting the experimental data of doubly charmed state $T_{cc}^{+}$ from our previous work. Our analysis indicates that the isospin symmetry is well preserved. We identify a deeply bound $T_{bb}^{-}$ state with quantum numbers $I(J^P)=0(1^{+})$, in contrast to the loosely bound $T_{cc}^{+}$. Additionally, we discover a resonant $T_{bb}^{-}$ state with $I(J^P)=1(1^{+})$. Furthermore, our investigation into the $\overline{B}{\overline{B}}^{*}\text{−}{\overline{B}}^{*}{\overline{B}}^{*}$ coupled channel effect reveals its important impact. The binding energy of the bound $I(J^P)=0(1^{+})$ states becomes deeper, while the resonant $T_{bb}^{-}$ state with $I(J^P)=1(1^{+})$ remains nearly unchanged.

In this paper we confront the color glass condensate and saturation approach of Contreras et al. [Non-linear equation in the re-summed next-to-leading order of perturbative QCD: The leading twist approximation, Eur. Phys. J. C 80, 1029 (2020)] with the experimental combined HERA data and obtain its parameters. The model includes two features that are in accordance with our theoretical knowledge of deep inelastic scattering. These consist of: ($i$) the use of analytical solution for the nonlinear Balitsky-Kovchegov evolution equation and (ii) the exponential behavior of the saturation momentum on the impact parameter $b$-dependence, characterized by $Q_s\propto \exp (-mb)$ which reproduces the correct behavior of the scattering amplitude at large $b$ in accord with Froissart theorem. The model results are then compared to data at small-$x$ for the structure function of the proton $F_2$, the longitudinal structure function $F_L$, the charm structure function $F_2^{c\overline{c}}$, the exclusive vector meson ($J/\psi ,\varphi ,\rho$) production and deeply virtual Compton scattering. We obtain a good agreement for the processes in a wide kinematic range of $Q^2$ at small-$x$. Our results provide a strong guide for finding an approach, based on color glass condensate and saturation effective theory for high-energy QCD, to make reliable predictions from first principles and for forthcoming experiments like the Electron Ion Collider and the LHeC.

Denoising diffusion models have gained prominence in various generative tasks, prompting their exploration for the generation of calorimeter responses. Given the computational challenges posed by detector simulations in high-energy physics experiments, the necessity to explore new machine-learning-based approaches is evident. This study introduces a novel graph-based diffusion model designed specifically for rapid calorimeter simulations. The methodology is particularly well-suited for low-granularity detectors featuring irregular geometries. We apply this model to the ATLAS dataset published in the context of the Fast Calorimeter Simulation Challenge 2022, marking the first application of a graph diffusion model in the field of particle physics.

In this letter, we consider a positive geometry conjectured to encode the loop integrand of four-point stress-energy correlators in planar $\mathcal{N}=4$ super Yang-Mills. Beginning with four lines in twistor space, we characterize a positive subspace to which an $\ell$-loop geometry is attached. The loop geometry then consists of $\ell$ lines in twistor space satisfying positivity conditions among themselves and with respect to the base. Consequently, the loop geometry can be viewed as fibration over a tree geometry. The fibration naturally dissects the base into chambers, in which the degree-$4\ell$ loop form is unique and distinct for each chamber. Interestingly, up to three loops, the chambers are simply organized by the six ordering of $x_{1,2}^2{x}_{3,4}^2$, $x_{1,4}^2{x}_{2,3}^2$, and $x_{1,3}^2{x}_{2,4}^2$. We explicitly verify our conjecture by computing the loop-forms in terms of a basis of planar conformal integrals up to $\ell =3$, which indeed yield correct loop integrands for the four-point correlator.

For compactifications of heterotic string theory, we elucidate simple cohomological conditions that lead to the vanishing of superpotential n-point couplings for all n. These results generalize some vanishing theorems for Yukawa couplings that have previously appeared in the literature to all higher orders. In some cases, these results are enough to show that certain fields do not appear in the perturbative superpotential at all. We illustrate our discussion with a number of concrete examples. In some cases, our results can be confirmed by showing that symmetries indeed forbid the couplings that vanish. In many, however, no such symmetries are known to exist and, as such, the infinite sets of vanishing couplings that are found are surprising from a four-dimensional perspective.

We use the free fermionic formulation of the heterotic string in four dimensions to study the vacuum structure and energy of nonsupersymmetric tachyon free models that correspond to compactifications of tachyonic vacua of the ten-dimensional heterotic string. We explore the class of heterotic $SO(10)$ nonsupersymmetric models constructed from the $\tilde{S}$ model in the free fermionic formalism and investigate the dependence of the potential on the geometric moduli. This paper will explore a sample of ${10}^9$ string vacua to find the frequency of viable models, classifying these vacua by the following fertility criteria: tachyon presence, number of spinorial $\mathbf{16}/\overline{\mathbf{16}}$ representations, vectorial $\mathbf{10}$ states, and top quark mass coupling compatibility. Of these we find those that mimic supersymmetric models with equal number of bosons and fermions at the massless level: $a_{00}=0$. Tachyon free models occur with a frequency of $5.309\times {10}^{-3}$. Furthermore, models that fulfil the rest of the phenomenological fertility conditions and the additional condition on $a_{00}$ occur with probability $4.0\times {10}^{-9}$ We analyze the partition functions and study the moduli dependence of such models, finding that almost all fertile models have finite, positive potential at the free fermionic point, with 2 out of 84 of the fertile cores having negative, finite potential. We demonstrate that the free fermionic point is not necessarily a minimum in the potential. This work provides further evidence that supersymmetry may not be a necessary ingredient of phenomenological models, recreating many of the desirable features of such models without employing supersymmetry.

In this work, we investigate an extended model of holographic superconductor by a nonlinear electrodynamic interaction coupled to a complex scalar field. This nonlinear interaction term can make a quantum phase transition at zero temperature with finite charge carrier density. By solving full equations of motion, we can construct various shapes of the superconducting phase in the phase diagram. With a specific choice of interaction coefficients, we can construct a phase diagram with a superconducting dome. Also, we find a new geometric solution inside the superconducting dome, which turns out to be a Lifshitz-type geometry. This geometry is characterized by a dynamical critical exponent, which plays a crucial role near the quantum critical point. We refer to this region of the phase diagram as a quantum critical region.

Despite numerous proposals investigating various properties of accelerated detectors in different settings, detecting the Unruh effect remains challenging due to the typically weak signal at achievable accelerations. For an atom with frequency gap ${\omega }_0$, accelerated in free space, significant acceleration-induced modification of properties like transition rates and radiative energy shifts requires accelerations of the order of ${\omega }_{0}c$. In this paper, we make the case for a suitably modified density of field states to be complemented by a judicious selection of the system property to be monitored. We study the radiative energy-level shift in inertial and uniformly accelerated atoms coupled to a massless quantum scalar field inside a cylindrical cavity. Uniformly accelerated atoms experience thermal correlations in the inertial vacuum, and the radiative shifts are expected to respond accordingly. We show that the noninertial contribution to the energy shift can be isolated and significantly enhanced relative to the inertial contribution by suitably modifying the density of field modes inside a cylindrical cavity. Moreover, we demonstrate that monitoring the radiative energy shift, as compared to transition rates, allows us to reap a stronger purely noninertial signal. We find that a purely noninertial radiative shift as large as 50 times the inertial energy shift can be obtained at small, experimentally achievable accelerations ($a\sim {10}^{-9}{\omega }_{0}c$) if the cavity’s radius $R$ is specified with a relative precision of $\delta R/R_0\sim {10}^{-7}$. Given that radiative shifts for inertial atoms have already been measured with high accuracy, we argue that the radiative energy-level shift is a promising observable for detecting Unruh thermality with current technology.

Bosonic stars represent a hypothetical exotic type of compact stellar object that could be observed from the gravitational signal of coalescing binaries in current and future gravitational wave detectors. There are two main families of bosonic stars, which depend on the nature that governs the particles that build them: Einstein-Klein-Gordon and Proca stars. We study the multipolar structure for both families of rotating objects, using realistic potentials with the aim of finding possible universal relations and, thus, a method that allows us to distinguish between these and other compact objects in the gravitational wave paradigm. We also show how certain relevant observables can be obtained for these hypothetical but well-motivated astrophysical objects.