We study the quasinormal modes of the spherically symmetric ($2+1$)-dimensional analog black hole, modeled by the “draining bathtub” fluid flow, and the ($3+1$)-dimensional canonical acoustic black hole. In the both cases the emphasis is on the accuracy. Formally, the radial equation describing perturbations of the ($2+1$)-dimensional black hole is a special case of the general master equation of the 5-dimensional Tangherlini black hole. Similarly, the ($3+1$)-dimensional equation can be obtained from the master equation of the 7-dimensional Tangherlini black hole. For the ($2+1$)-dimensional analog black hole we used three major techniques: the higher-order Wentzel–Kramers–Brillouin (WKB) method with the Padé summation, the Hill-determinant method and the continued fraction method, the latter two with the convergence acceleration. In the ($3+1$)-dimensional case, we propose the simpler recurrence relations and explicitly demonstrate that both recurrences, i.e., the eight-term and the six-term recurrences yield identical results. Since the application of the continued-fraction method require five (or three) consecutive Gauss eliminations, we decided not to use this technique in the ($3+1$)-dimensional case. Instead, we used the Hill-determinant method in the two incarnations and the higher-order WKB. We accept the results of our calculations if at least two (algorithmically) independent methods give the same answer to some prescribed accuracy. Our results correct and extend the results existing in the literature and we believe that we approached assumed accuracy of 9 decimal places. In most cases, there is perfect agreement between all the methods; however, in a few cases, the performance of the higher-order WKB method is slightly worse.

This study examines the formulation of a singularity theorem for timelike curves including torsion, and establishes the foundational framework necessary for its derivation. We begin by deriving the relative acceleration for an arbitrary congruence of timelike curves. The resulting “deviation equation” offers an alternative pathway to the well-known Raychaudhuri equation with torsion. Conjugate points are then introduced and analyzed in relation to the behavior of the scalar expansion. Together with the sensible requirement of hypersurface orthogonality, the Raychaudhuri equation is examined for several specific cases of torsion that are prominent in the literature. Our findings indicate that a totally antisymmetric torsion tensor does not influence the behavior of the congruence of timelike curves. Finally, we formulate a singularity theorem for timelike curves and highlight the critical requirement of nonautoparallel curves.

In this work, we quantify the cosmological signatures of dark energy radiation—a novel description of dark energy, which proposes that the dynamical component of dark energy is comprised of a thermal bath of relativistic particles sourced by thermal friction from a slowly rolling scalar field. For a minimal model with particle production emerging from first principles, we find that the abundance of radiation sourced by dark energy can be as large as ${\mathrm{\Omega }}_{\mathrm{DER}}=0.03$, exceeding the bounds on relic dark radiation by three orders of magnitude. Although the background and perturbative evolution of dark energy radiation are distinct from Quintessence, we find that current and near-future cosmic microwave background and supernova data will not distinguish these models of dark energy. We also find that our constraints on all models are dominated by their impact on the expansion rate of the Universe. Considering extensions that allow the dark radiation to populate neutrinos, axions, and dark photons, we evaluate the direct detection prospects of a thermal background comprised of these candidates consistent with cosmological constraints on dark energy radiation. Our study indicates that a resolution of $\sim 6\mathrm{meV}$ is required to achieve sensitivity to relativistic neutrinos compatible with dark energy radiation in a neutrino capture experiment on tritium. We also find that dark matter axion experiments lack sensitivity to a relativistic thermal axion background, even if enhanced by dark energy radiation, and dedicated search strategies are required to probe new parameter space. We derive constraints arising from a dark photon background from oscillations into visible photons, and find that viable parameter space can be explored with the late dark energy radiation experiment.

High-number-density tracers of large-scale structure, such as the HI-rich galaxies measured by 21 cm intensity mapping, have low sampling noise, making them particularly promising as cosmological probes. At large scales, this sampling noise can be subdominant to other scale-independent contributions to the power spectrum; such contributions arise from nonlinear bias, and exceed the sampling noise if at least one of the associated bias coefficients is sufficiently large. This has important consequences for cosmological constraints obtained from such tracers, since it indicates that using the power spectrum does not lead to optimal constraints even in the linear regime. In this paper, we provide a conservative estimate of the possible improvement in constraining power of a 21 cm survey if one were to use an optimal analysis strategy (such as field-level analysis), where only the true sampling noise enters the error budget. We find that improvements in uncertainties on some cosmological parameters can be as large as 50%, depending on redshift, foreground cleaning efficiency, scales used in the analysis, and instrumental noise. One byproduct of our work is measurements of bias parameters and stochasticity for neutral hydrogen in the IllustrisTNG simulation over a wide range of redshifts; we provide simple fitting formulas for these measurements. Our results motivate further exploration of new optimal analysis techniques and provide important insights into the constraining power of current and future 21 cm surveys.

We investigate two classes of inflationary models, which lead to a stiff period after inflation that boosts the signal of primordial gravitational waves (GWs). In both families of models studied, we consider an oscillating scalar condensate, which when far away from the minimum is overdamped by a warped kinetic term, á la $\alpha$-attractors. This leads to successful inflation. The oscillating condensate is in danger of becoming fragmented by resonant effects when nonlinearities take over. Consequently, the stiff phase cannot be prolonged enough to enhance primordial GWs at frequencies observable in the near future for low orders of the envisaged scalar potential. However, this is not the case for a higher-order scalar potential. Indeed, we show that this case results in a boosted GW spectrum that overlaps with future observations without generating too much GW radiation to destabilize big bang nucleosynthesis. For example, taking $\alpha =\mathcal{O}(1)$, we find that the GW signal can be safely enhanced up to ${\mathrm{\Omega }}_{\mathrm{GW}}(f)\sim {10}^{-11}$ at frequency $f\sim {10}^2\mathrm{Hz}$, which will be observable by the Einstein Telescope. Our mechanism ends up with a characteristic GW spectrum, which if observed, can lead to the determination of the inflation energy scale, the reheating temperature, and the shape (steepness) of the scalar potential around the minimum.

We study the impact on the trajectory of high-energy cosmic-ray protons of scattering off the cosmic dark matter. We compute the scattering angle as a function of the cosmic-ray energy, of the dark matter mass, and of the interaction strength for a few representative choices for the relevant interaction cross section. We find that the typical deflection angle over the cosmic ray path is largely independent of the dark matter mass. Given existing limits on the interaction strength, we compute the average deflection angle. We find that for large interaction cross sections and low cosmic ray energies, the predicted deflection angle is much larger than the angular resolution of very high-energy cosmic-ray observatories such as Pierre Auger.

A quantitative analysis of model uncertainties for calculations of the maximum depth of proton-initiated extensive air showers (EAS) has been performed. Staying within the standard physics picture and using the conventional approach to the treatment of high-energy interactions, we found that present uncertainties on the energy dependence of the inelastic cross section, the rate of diffraction, and the inelasticity of hadronic collisions allow one to increase the predicted average EAS maximum depth by about $10\mathrm{g}/{\mathrm{cm}}^2$. Invoking more exotic assumptions regarding a potentially significant modification of the parton hadronization procedure by hypothetical collective effects, we were able to change drastically the predicted energy dependence of the inelasticity of proton-air interactions and to increase thereby the predicted EAS maximum depth by up to $\simeq 30\mathrm{g}/{\mathrm{cm}}^2$. However, those latter modifications are disfavored by the data of the LHCf experiment, regarding forward neutron production in proton-proton collisions at the Large Hadron Collider, and by measurements of the muon production depth by the Pierre Auger Observatory.

In detuned optical cavities, the radiation pressure force acting on the mirrors depends on their displacements. This is equivalent to the rigidity (the optical spring), inserted between the mirrors. This effect can be used for optimization of the mechanical susceptibility of probe mirrors in high-precision force sensors. However, in some cases, the use of detuned cavities or even just any high-finesse cavities could be problematic due to technological constraints. We consider a new type of the optical spring that does not require the cavity (but can use a resonance tuned one to increase the optomechanical coupling). Instead, it uses the double interaction of the probing light with the mechanical object. An important advantage of this type of the optical spring is that it allows one to tune the optomechanical setup in a real time without affecting its core optics. We propose two possible implementation of this concept, suitable, respectively, for the atomic spin ensembles and for the laser gravitational-wave detectors.

The Pierre Auger Observatory is the most sensitive instrument to detect photons with energies above $10^{17}\mathrm{eV}$. It measures extensive air showers generated by ultrahigh energy cosmic rays using a hybrid technique that exploits the combination of a fluorescence detector with a ground array of particle detectors. The signatures of a photon-induced air shower are a larger atmospheric depth of the shower maximum ($X_{\max }$) and a steeper lateral distribution function, along with a lower number of muons with respect to the bulk of hadron-induced cascades. In this work, a new analysis technique in the energy interval between 1 and 30 EeV ($1\mathrm{EeV}=10^{18}\mathrm{eV}$) has been developed by combining the fluorescence detector-based measurement of $X_{\max }$ with the specific features of the surface detector signal through a parameter related to the air shower muon content, derived from the universality of the air shower development. No evidence of a statistically significant signal due to photon primaries was found using data collected in about 12 years of operation. Thus, upper bounds to the integral photon flux have been set using a detailed calculation of the detector exposure, in combination with a data-driven background estimation. The derived 95% confidence level upper limits are 0.0403, 0.01113, 0.0035, 0.0023, and $0.0021{\mathrm{km}}^{-2}{\mathrm{sr}}^{-1}{\mathrm{yr}}^{-1}$ above 1, 2, 3, 5, and 10 EeV, respectively, leading to the most stringent upper limits on the photon flux in the EeV range. Compared with past results, the upper limits were improved by about 40% for the lowest energy threshold and by a factor 3 above 3 EeV, where no candidates were found and the expected background is negligible. The presented limits can be used to probe the assumptions on chemical composition of ultrahigh energy cosmic rays and allow for the constraint of the mass and lifetime phase space of super-heavy dark matter particles.

It is known that the Fierz identities predict that the Gross-Neveu and Thirring models should be equivalent when describing systems composed of a single fermionic flavor, $N=1$. Here, we consider the planar version of both models within the framework of the optimized perturbation theory at the two-loop level, in order to verify if the predicted equivalence emerges explicitly when different temperature and density regimes are considered. At vanishing densities, our results indicate that both models indeed describe exactly the same thermodynamics, provided that $N=1$. However, at finite chemical potentials we find that the $N=1$ Fierz equivalence no longer holds. After examining the relevant thermodynamic potentials, we have identified the contributions which lead to this puzzling discrepancy. Finally, we discuss different frameworks in which this (so far open) problem could be further understood and eventually circumvented.

We develop a general framework for studying the spin alignment ${\rho }_{00}$ for flavorless vector mesons by using the gauge/gravity duality. Focusing on the dilepton production through vector meson decay, we derive the relation between production rates at each spin channel and meson’s spectral function in a thermal medium, which can be evaluated by holographic models for a strongly coupled system. As examples, we study ${\rho }_{00}$ for $J/\psi$ and $\varphi$ mesons, induced by the relative motion to a thermal background, within the soft-wall model. Spectral functions for $J/\psi$ at $T=150\mathrm{MeV}$ have significant resonance peaks, indicating that $c-\overline{c}$ can exist as quasistable $J/\psi$ mesons. However, no significant peaks for the $\varphi$ meson are observed at the same temperature, implying that $\varphi$ mesons are melting down at this temperature and spectral functions are interpreted as probabilities of unstable $s-\overline{s}$ pairs. These pairs are related to free-streaming $\varphi$ mesons by an instantaneous freeze-out assumption, which is performed by sandwiching the in-medium spectral function between the meson’s free-streaming propagators. Then only states with invariant masses closing to the meson’s vacuum mass survive during the freeze-out stage and contribute to final results. We show that ${\rho }_{00}$ in the helicity frame for $J/\psi$ and $\varphi$ mesons have positive and negative deviations from $1/3$ at $T=150\mathrm{MeV}$, respectively, which consequently leads to different properties for their global spin alignments.

The parity-expanded variational analysis (PEVA) technique enables the isolation of opposite-parity eigenstates at finite momentum. The approach has been used to perform the first lattice QCD calculations of excited-baryon form factors. In particular, these calculations show that the low-lying odd-parity nucleon excitations are described well by constituent quark models at moderate $u$ and $d$ quark masses approaching the strange quark mass. Herein, we extend the PEVA technique to establish a formalism for the determination of odd-parity nucleon electromagnetic transition form factors in lattice QCD. The formalism is implemented in the first calculation of the helicity amplitudes for transitions from the ground state nucleon to the first two odd-parity excitations. Through a comparison with constituent quark-model calculations of these amplitudes, these new results give important insight into the structure of these excitations. This work is a critical step towards confronting experimental electroproduction amplitudes for the $N^{*}(1535)$ and $N^{*}(1650)$ resonances with ab-initio lattice QCD calculations.

We present the first numerical implementation of the massive symmetric-momentum-subtraction (mSMOM) renormalization scheme and use it to calculate the charm-quark mass. Based on ensembles with three flavors of dynamical domain-wall fermions with lattice spacings in the range 0.11–0.08 fm, we demonstrate that the mass scale which defines the mSMOM scheme can be chosen such that the extrapolation has significantly smaller discretization effects than the SMOM scheme. Converting our results to the $\overline{\mathrm{MS}}$ scheme we obtain ${\overline{m}}_c(3\mathrm{GeV})=1.008(13)\mathrm{GeV}$ and ${\overline{m}}_c({\overline{m}}_c)=1.292(12)\mathrm{GeV}$.

We have calculated the valence quark distributions of the lightest pseudoscalar meson, pions, in the isospin asymmetric nuclear matter at zero and finite temperature employing a light-cone quark model. The medium modifications in the pion properties have been incorporated through the effective quark masses computed using the chiral SU(3) quark mean field model. We have primarily focused on the impact of isospin asymmetric medium on the distribution amplitudes (DAs) and parton distribution functions (PDFs) of a valence quark for different baryon density and temperature values. Also, the DAs and PDFs have been evolved to $Q^2=10{\mathrm{GeV}}^2$ and $Q^2=16{\mathrm{GeV}}^2$ for different densities of nuclear medium and results have been compared with the available experimental data. The DAs and PDFs are found to modify substantially as a function of baryon density as compared to temperature and isospin asymmetry of the medium.

Utilizing an equiparticle model with both linear confinement and leading-order perturbative interactions, we obtain systematically the properties of strangelets and nonstrange quark matter ($ud\mathrm{QM}$) nuggets at various baryon ($A$) and charge ($Z$) numbers, where the detailed single-quark-energy levels are fixed by solving Dirac equations in mean-field approximation. We then examine the structures of compact dwarfs made of light strangelets or $ud\mathrm{QM}$ nuggets forming body-centered cubic lattices in a uniform electron background. Despite that the strangelets and $ud\mathrm{QM}$ nuggets generally become more stable at larger $A$, the compact dwarfs are still stable since the fusion reactions between those objects do not take place in the presence of a Coulomb barrier, which is similar to the cases of light nuclei in normal white dwarfs. If $ud\mathrm{QM}$ dwarfs or strangelet dwarfs are covered with normal matter, their masses and radii become larger but do not exceed those of ordinary white dwarfs. Finally, we investigate the radial oscillation frequencies of $ud\mathrm{QM}$ dwarfs and strangelet dwarfs and find that their frequencies are typically higher than traditional white dwarfs. The stability of compact dwarfs are then analyzed by examining radial oscillation frequencies of the fundamental mode, where compact dwarfs covered by normal matter are still stable.

In the framework of a one-boson-exchange model, we carry out a comprehensive investigation of the ${\mathrm{\Xi }}_{c}N/{\mathrm{\Lambda }}_c\mathrm{\Sigma }/{\mathrm{\Xi }}_c^{\prime }N/{\mathrm{\Sigma }}_c\mathrm{\Lambda }/{\mathrm{\Xi }}_c^{*}N/{\mathrm{\Sigma }}_c^{*}\mathrm{\Lambda }/{\mathrm{\Sigma }}_c\mathrm{\Sigma }/{\mathrm{\Sigma }}_c^{*}\mathrm{\Sigma }$ interactions. We consider the $S\text{−}D$-wave mixing effects and the coupled-channel effects to derive the relevant effective potentials. Our results can predict several possible charm-strange deuteronlike ${\mathrm{\Xi }}_c^{{(}^{\prime },*)}N$ hexaquarks, the ${\mathrm{\Xi }}_c^{\prime }N$ molecules with $I(I^P)=0(0^{+})$, $0(1^{+})$, $1(1^{+})$, the ${\mathrm{\Xi }}_c^{*}N$ molecules with $0(1^{+})$, $0(2^{+})$, $1(2^{+})$, and the coupled ${\mathrm{\Xi }}_{c}N/{\mathrm{\Xi }}_c^{\prime }N/{\mathrm{\Xi }}_c^{*}N/{\mathrm{\Sigma }}_c\mathrm{\Sigma }/{\mathrm{\Sigma }}_c^{*}\mathrm{\Sigma }$ molecule with $0(1^{+})$. We expect the experiments to search for our predictions of the ${\mathrm{\Xi }}_c^{(\prime ,*)}N$ bound states.

For the first time, the exact analytic integration of the product between the Kuraev-Fadin radiative function and the Born-level cross section has been achieved for $e^{+}{e}^{-}$ annihilation near a narrow resonance. The analytic result is in a perfect agreement with the one obtained through direct numerical integration. The extraction of resonance parameters is demonstrated through the unfolding of the initial state radiation effect. The analytic integration significantly accelerates the regression process by more than 160 times compared to numerical integration. Moreover, it facilitates the determination of experimental measurements for physical parameters, such as the two-dimensional confidence region of the branching fraction and the relative phase between the strong and electromagnetic amplitudes, within just one hour instead of one week typically required for numerical integration.

This work explores the use of differentiable programming to integrate domain knowledge, in the form of domain specific software, into neural networks to develop scientific machine learning systems. We propose a differentiable vertex fitting algorithm that estimates the crossing point of multiple curves. In the high energy physics setting, these curves are defined by particle equations of motion and the crossing point represents the origin of particle production. This differentiable vertex fitting algorithm can be seamlessly integrated into neural networks, and we show its utility and efficacy in the high energy physics application of the classification of jets, i.e., collimated streams of particles in particle detectors whose originating parent particle we aim to classify. We demonstrate how differentiable vertex fitting can be integrated into larger transformer-based models for jet flavor tagging and show improvements in heavy flavor jet classification when compared to baseline models.

Using data samples with an integrated luminosity of $4.67{\mathrm{fb}}^{-1}$ collected by the BESIII detector operating at the BEPCII Collider, we search for the process $e^{+}{e}^{-}\to {\eta }^{\prime }\psi (2S)$ at center-of-mass energies from 4.66 to 4.95 GeV. No significant signal is observed, and upper limits for the Born cross sections ${\sigma }^B(e^{+}{e}^{-}\to {\eta }^{\prime }\psi (2S))$ at the 90% confidence level are determined.