We construct quasinormal modes for neutron stars in $R^2$ gravity in the Einstein frame, considering scalar masses in the sub-neV range. In particular, we investigate the fundamental quadrupole fluid $f$ modes and the dipole fluid $F$ modes. Employing six equations of state covering matter content with nucleons, hyperons, and quarks, we then propose universal relations for the quadrupole $f$ modes and dipole $F$ modes. The dipole $F$ modes are ultralong lived and, for the lower scalar masses, their frequencies are inversely proportional to the corresponding Compton wavelength.

We present a calculation of the Detweiler redshift factor in binary black hole simulations based on its relation to the surface gravity. The redshift factor has far-reaching applications in analytic approximations, gravitational self-force calculations, and conservative two-body dynamics. By specializing to nonspinning, quasicircular binaries with mass ratios ranging from $m_A/m_B=1$ to $m_A/m_B=9.5$ we are able to recover the leading small-mass-ratio (SMR) prediction with relative differences of order ${10}^{-5}$ from simulations alone. The next-to-leading order term that we extract agrees with the SMR prediction arising from self-force calculations, with differences of a few percent. These deviations from the first-order conservative prediction are consistent with nonadiabatic effects that can be accommodated in an SMR expansion. This fact is also supported by a comparison to the conservative post-Newtonian prediction of the redshifts. For the individual redshifts, a reexpansion in terms of the symmetric mass ratio $\nu$ does not improve the convergence of the series. However we find that when looking at the sum of the redshift factors of both back holes, $z_A+z_B$, which is symmetric under the exchange of the masses, a reexpansion in $\nu$ accelerates its convergence. Our work provides further evidence of the surprising effectiveness of SMR approximations in modeling even comparable mass binary black holes.

We calculate the eccentricity dependence of the high-order post-Newtonian (PN) series for the generalized redshift invariant $⟨u^t{⟩}_{\tau }$ for eccentric-orbit extreme-mass-ratio inspirals on a Schwarzschild background. These results are calculated within first-order black hole perturbation theory using Regge-Wheeler-Zerilli (RWZ) gauge. Our Mathematica code is based on a familiar procedure, using PN expansion of the Mano-Suzuki-Takasugi analytic function formalism for $l$ modes up to a certain maximum and then using a direct general-$l$ PN expansion of the RWZ equation for arbitrarily high $l$. We calculate dual expansions in PN order and in powers of eccentricity, reaching 10PN relative order and $e^{20}$. Detailed knowledge of the eccentricity expansion at each PN order allows us to find within the eccentricity dependence numerous closed-form expressions and multiple infinite series with known coefficients. We find leading logarithm sequences in the PN expansion of the redshift invariant that reflect a similar behavior in the PN expansion of the energy flux to infinity. A set of flux terms and special functions that appear in the energy flux, like the Peters-Mathews flux itself, are shown to reappear in the redshift PN expansion.

We analyze the properties that any late-time modification of the $\mathrm{\Lambda }\mathrm{CDM}$ expansion history must have in order to consistently solve both the $H_0$ and the ${\sigma }_8$ tensions. Taking a model-independent approach, we obtain a set of necessary conditions that can be applied to any late-time extension whose main effect is a deviation from the $\mathrm{\Lambda }\mathrm{CDM}$ background. Our results are fully analytical and merely based on the assumptions that the deviations from the $\mathrm{\Lambda }\mathrm{CDM}$ background remain small. For the concrete case of a dark energy fluid with equation of state $w(z)$, we derive the following general requirements: (i) Solving the $H_0$ tension demands $w(z)<-1$ at some $z$ (ii) Solving both the $H_0$ and ${\sigma }_8$ tensions requires $w(z)$ to cross the phantom divide. Finally, we also allow for small deviations on the effective gravitational constant. In this case, our method is still able to constrain the functional form of these deviations.

The strongest existing constraints on primordial black holes with masses in the range of $m_{\mathrm{BH}}\sim {10}^{15}–{10}^{17}\mathrm{g}$ have been derived from measurements of the local cosmic-ray electron-positron flux by Voyager 1, and MeV-scale gamma-ray observations of the inner Galaxy by COMPTEL and INTEGRAL. In this paper, we evaluate the sensitivity of future MeV-scale gamma-ray telescopes such as e-ASTROGAM or AMEGO to Hawking radiation. We show that such an instrument would be able to provide the strongest constraints on black holes in the mass range of $m_{\mathrm{BH}}\sim (0.6–20)\times {10}^{16}\mathrm{g}$, typically exceeding current constraints by approximately two orders of magnitude. In scenarios in which the observed 511 keV excess is the result of Hawking radiation, we find that e-ASTROGAM or AMEGO would not only be able to detect the Hawking radiation from the inner Galaxy, but could precisely measure the abundance and mass distribution of the black holes responsible for this signal.

We present here the latest development of a machine-learning pipeline for premerger alerts from gravitational waves coming from binary neutron stars (BNSs). This work starts from the convolutional neural networks introduced in [Baltus et al., Phys. Rev. D 103, 102003 (2021)] that searched for the early inspirals in simulated Gaussian noise colored with the design-sensitivity power-spectral density of LIGO. Our new network is able to search for any BNS with a chirp mass between 1 and $3M_{\odot }$, it can take into account all the detectors available, and it can see the events even earlier than the previous one. We study the performance of our method in three different scenarios: colored Gaussian noise based on the O3 sensitivity, real O3 noise, colored Gaussian noise based on the predicted O4 sensitivity. We show that our network performs almost as well in non-Gaussian noise as in Gaussian noise: our method is robust with respect to glitches and artifacts present in real noise. Although it would not have been able to trigger on the BNSs detected during O3 because their signal-to-noise ratio was too weak, we expect our network to find around 3 BNSs during O4 with a time before the merger between 3 and 88 s in advance.

The standard approach for predicting thermal noise in optical mirrors using the fluctuation-dissipation theorem requires knowledge of the level of all significant sources of mechanical loss occurring at the oscillation amplitudes of thermal noise. Using a gentle nodal suspension system read out by a Michelson interferometer, we tested the amplitude-dependence of loss in $\mathrm{GaAs}/{\mathrm{Al}}_{0.92}{\mathrm{Ga}}_{0.08}\mathrm{As}$ multilayer optical coatings on silica substrates in the range from just above the rms thermal noise amplitude up to amplitudes typical of ringdown measurements: ${10}^{-1}–{10}^3$ picometers. None of the three samples tested showed any significant amplitude dependence over this range.

We review various methods used to estimate uncertainties in quantum correlation functions, such as parton distribution functions (PDFs). Using a toy model of a PDF, we compare the uncertainty estimates yielded by the traditional Hessian and data resampling methods, as well as from explicitly Bayesian analyses using nested sampling or hybrid Markov chain Monte Carlo techniques. We investigate how uncertainty bands derived from neural network approaches depend on details of the network training, and how they compare to the uncertainties obtained from more traditional methods with a specific underlying parametrization. Our results show that utilizing a neural network on a simplified example of PDF data has the potential to inflate uncertainties, in part due to the cross-validation procedure that is generally used to avoid overfitting data.

Not only are Casimir interaction entropies not guaranteed to be positive, but also, more strikingly, Casimir self-entropies of bodies can be negative. Here, we attempt to interpret the physical origin and meaning of these negative self-entropies by investigating the Casimir self-entropy of a neutral spherical nanoparticle. After extracting the polarizabilities of such a particle by examining the asymptotic behavior of the scattering Green’s function, we compute the corresponding free energy and entropy. Two models for the nanoparticle, namely a spherical plasma $\delta$-function shell and a homogeneous dielectric/diamagnetic ball, are considered at low temperature, because that is all that can be revealed from a nanoparticle perspective. The second model includes a contribution to the entropy from the bulk free energy, referring to the situation where the medium inside or outside the ball fills all space, which must be subtracted on physical grounds in order to maintain consistency with van der Waals interactions, corresponding to the self-entropy of each bulk. (The van der Waals calculation is described in Appendix A.) The entropies so calculated agree with known results in the low-temperature limit, appropriate for a small particle, and are negative. But we suggest that the negative self-entropy is simply an interaction entropy, the difference between the total entropy and the blackbody entropy of the two bulks, outside or inside of the nanosphere. The vacuum entropy is always positive and overwhelms the interaction entropy. Thus the interaction entropy can be negative, without contradicting the principles of statistical thermodynamics. Given the intrinsic electrical properties of the nanoparticle, the self-entropy arises from its interaction with the thermal vacuum permeating all space. Because the entropy of blackbody radiation by itself plays an important role, it is also discussed, including dispersive effects, in detail.

The baryonic form factor of charged pions is studied in detail in the Nambu–Jona-Lasinio model with constituent quarks, where the spontaneously broken chiral symmetry is the key dynamical ingredient guaranteeing the would-be Goldstone boson nature of the pseudoscalar mesons octet. In general, this form factor arises when the isospin symmetry is broken, which is the case if the $u$ and $d$ quark masses are split, as in the real world, or if the electromagnetic effects were taken into account. We obtain estimates for this basic property of the pion resulting from the quark mass splitting for a range of model parameters, and importantly, for different pion masses, going up to the values used in lattice QCD. We find very stable model results, with the mean square radius of ${\pi }^{+}$ in the range $(0.05–0.07\mathrm{fm}{)}^2$. From charge conjugation, the baryonic form factor of ${\pi }^{+}$ and ${\pi }^{-}$ are equal and opposite. We also obtain the transverse-coordinate, relativistically invariant baryonic density of the charged pion. In ${\pi }^{+}$, the inner region carries a negative, and the outside—a positive baryon number density, both cancelling to zero, as obviously the pion carries no net baryon charge. We also carry out an analogous analysis for the kaon, where the effect is much larger due to the sizable $s$ and $u/d$ quark mass splitting. We discuss the prospects of lattice QCD measurements of the baryonic form factors of charged pions and kaons.

We develop a unified algebraic model which satisfactorily describes the internal structure of pion and kaon as well as heavy quarkonia (${\eta }_c$ and ${\eta }_b$). For each of these mesons, we compute their generalized parton distributions (GPDs), built through the overlap representation of their light front wave function, tightly constrained by the modern and precise knowledge of their quark distribution amplitudes. From this three-dimensional knowledge of mesons, we deduce parton distribution functions (PDFs) as well as electromagnetic form factors and construct the impact parameter space GPDs. The PDFs for mesons formed with light quarks are then evolved from the hadronic scale of around 0.3 to 5.2 GeV, probed in experiments. We make explicit comparisons with experimental results available and with earlier theoretical predictions.

Central to understanding the nonperturbative, intrinsic partonic nature of hadron structure are the concepts of transverse momentum dependent (TMD) parton distribution and fragmentation functions. A TMD factorization approach to the phenomenology of semi-inclusive processes that includes evolution, higher orders, and matching to larger transverse momentum is ultimately necessary for reliably connecting with phenomenologically extracted nonperturbative structures, especially when widely different scales are involved. In this paper, we will address some of the difficulties that arise when phenomenological techniques that were originally designed for very high energy applications are extended to studies of hadron structures, and we will solidify the connection between standard high energy TMD implementations and the more intuitive, parton model based approaches to phenomenology that emphasize nonperturbative hadron structure. In the process, we will elaborate on differences between forward and backward TMD evolution, which in the context of this paper, we call “bottom-up” and “top-down” approaches, and we will explain the advantages of a bottom-up strategy. We will also emphasize and clarify the role of the integral relations that connect TMD and collinear correlation functions. We will show explicitly how they constrain the nonperturbative “$g$-functions” of standard Collins-Soper-Sterman implementations of TMD factorization. This paper is especially targeted toward phenomenologists and model builders who are interested in merging specific nonperturbative models and calculations (including lattice QCD) with TMD factorization at large $Q$. Our main result is a recipe for incorporating nonperturbative models into TMD factorization and for constraining their parameters in a way that matches perturbative QCD and evolution.

In this work we report the calculation of the charged current total and differential cross sections for weak pion production with neutrinos and antineutrinos, with the final pion-nucleon pair invariant mass $W_{\pi N}\lesssim 2\mathrm{GeV}$. Our results are compared with the recent reanalyzed data from the old bubble chamber experiments, that solved the discrepancy between the Argonne National Laboratory and Brookhaven National Laboratory data. We implement a model previously tested for the cuts $W_{\pi N}<1.4$, 1.6 GeV, which explicitly includes resonances in the first and second resonance regions within different approaches for the resonances self-energy and $\frac{3}{2}$ vertexes and propagators, a fact not usually analyzed. Our model leans on consistently effective Lagrangians that generate resonant amplitudes together with nonresonant and resonant backgrounds. Effects of hadrons’ finite extension and more energetic resonances correspond to the emitted pion-nucleon invariant mass in the $1.6<W_{\pi N}<2\mathrm{GeV}$ region are taking into account using appropriate form factors in consistency with previous results on neutral current pion production calculations. Our results reproduce well the reanalyzed data without cuts and are compared with other models.

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is a pulsed source of neutrons and, as a by-product of this operation, an intense source of pulsed neutrinos via stopped-pion decay. The COHERENT collaboration uses this source to investigate coherent elastic neutrino-nucleus scattering and other physics with a suite of detectors. This work includes a description of our geant4 simulation of neutrino production at the SNS and the flux calculation which informs the COHERENT studies. We estimate the uncertainty of this calculation at the $\sim 10\%$ level based on validation against available low-energy ${\pi }^{+}$ production data.

We use exact diagonalization to study energy level statistics and out-of-time-order correlators (OTOCs) for the simplest supersymmetric extension ${\widehat{H}}_S={\widehat{H}}_B\otimes I+{\widehat{x}}_1\otimes {\sigma }_1+{\widehat{x}}_2\otimes {\sigma }_3$ of the bosonic Hamiltonian ${\widehat{H}}_B={\widehat{p}}_1^2+{\widehat{p}}_2^2+{\widehat{x}}_1^2{\widehat{x}}_2^2$. For a long time, this bosonic Hamiltonian was considered one of the simplest systems which exhibit dynamical chaos both classically and quantum-mechanically. Its structure closely resembles that of spatially compactified pure Yang-Mills theory. Correspondingly, the structure of our supersymmetric Hamiltonian is similar to that of spatially compactified supersymmetric Yang-Mills theory, also known as the Banks-Fischler-Shenker-Susskind (BFSS) model. We present numerical evidence that a continuous energy spectrum of the supersymmetric model leads to monotonous growth of OTOCs down to the lowest temperatures, a property that is also expected for the BFSS model from holographic duality. We find that this growth is saturated by low-energy eigenstates with effectively one-dimensional wave functions and a completely nonchaotic energy level distribution. We observe a sharp boundary separating these low-energy states from the bulk of chaotic high-energy states. Our data suggest, although with limited confidence, that at low temperatures the OTOC growth might be exponential over a finite range of time, with the corresponding Lyapunov exponent scaling linearly with temperature. In contrast, the gapped low-energy spectrum of the bosonic Hamiltonian leads to oscillating OTOCs at low temperatures without any signatures of exponential growth. We also find that the OTOCs for the bosonic Hamiltonian are never sufficiently close to the classical Lyapunov distance. On the other hand, the OTOCs for the supersymmetric system agree with the classical limit reasonably well over a finite range of temperatures and evolution times.

We examine the dynamics of noncommutative instantons of instanton number 2 and commutative instantons of instanton number 3 in 5D super Yang-Mills theory. We begin by detailing the construction of the $1/4$-Bogamolyni-Prasad-Somerfeldt instanton solutions, their moduli space, and the moduli space potential using an explicit parametrization of the moduli space coordinates in terms of the biquaternions. We then go on to numerically analyze the dynamics on the moduli spaces we have constructed, discussing some of the numerical issues which arose, and describing the numerical algorithm we developed to solve them.

In full Horndeski theories, we show that the static and spherically symmetric black hole (BH) solutions with a static scalar field $\varphi$ whose kinetic term $X$ is nonvanishing on the BH horizon are generically prone to ghost/Laplacian instabilities. We then search for asymptotically Minkowski hairy BH solutions with a vanishing $X$ on the horizon free from ghost/Laplacian instabilities. We show that models with regular coupling functions of $\varphi$ and $X$ result in no-hair Schwarzschild BHs in general. On the other hand, the presence of a coupling between the scalar field and the Gauss-Bonnet (GB) term $R_{\mathrm{GB}}^2$, even with the coexistence of other regular coupling functions, leads to the realization of asymptotically Minkowski hairy BH solutions without ghost/Laplacian instabilities. Finally, we find that hairy BH solutions in power-law $F(R_{\mathrm{GB}}^2)$ gravity are plagued by ghost instabilities. These results imply that the GB coupling of the form $\xi (\varphi )R_{\mathrm{GB}}^2$ plays a prominent role for the existence of asymptotically Minkowski hairy BH solutions free from ghost/Laplacian instabilities.

In a strong electromagnetic field, gravitational waves are converted into electromagnetic waves of the same frequency, and vice versa. Here, we calculate scattering and conversion cross sections for a planar wave impinging upon a Reissner-Nordström black hole in electrovacuum, using the partial-wave expansion and numerical methods. We show that, at long wavelengths, the conversion cross section matches that computed by Feynman-diagram techniques, and at short wavelengths, the essential features are captured by a geometric-optics approximation. We demonstrate that the converted flux can exceed the scattered flux at large scattering angles, for highly-charged black holes. In the short-wavelength regime, the conversion effect may be understood in terms of a conversion phase that accumulates along a ray. We compute the scattering angle for which the converted and scattered fluxes are equal, as a function of charge-to-mass ratio; and we show that this scattering angle approaches 90° in the extremal limit.

Gravitational wave observations of large mass ratio compact binary mergers like GW190814 highlight the need for reliable, high-accuracy waveform templates for such systems. We present nrhybsur2dq15, a new surrogate model trained on hybridized numerical relativity (NR) waveforms with mass ratios $q\le 15$ and aligned spins $|{\chi }_{1z}|\le 0.5$ and ${\chi }_{2z}=0$. We target the parameter space of GW190814-like events as large mass ratio NR simulations are very expensive. The model includes the (2, 2), (2, 1), (3, 3), (4, 4), and (5, 5) spin-weighted spherical harmonic modes and spans the entire LIGO-Virgo bandwidth (with $f_{\mathrm{low}}=20\mathrm{Hz}$) for total masses $M\gtrsim 9.5M_{\odot }$. nrhybsur2dq15 accurately reproduces the hybrid waveforms, with mismatches below $\sim 2\times {10}^{-3}$ for total masses $10M_{\odot }\le M\le 300M_{\odot }$. This is at least an order of magnitude improvement over existing semianalytical models for GW190814-like systems. Finally, we reanalyze GW190814 with the new model and obtain source parameter constraints consistent with previous work.

We construct cosmological models based on a complex scalar field with a power-law potential $V=\frac{K}{\gamma -1}(\frac{m}{\hslash }{)}^{2\gamma }|\phi {|}^{2\gamma }$ associated with a polytropic equation of state $P=K{\rho }^{\gamma }$ (the potential associated with an isothermal equation of state $P=\rho k_{B}T/m$ is $V=\frac{m{k}_{B}T}{{\hslash }^2}|\phi {|}^2[\ln (m^2|\phi {|}^2/{\rho }_{*}{\hslash }^2)-1]$ and the potential associated with a logotropic equation of state $P=A\ln (\rho /{\rho }_P)$ is $V=-A[\ln (m^2|\phi {|}^2/{\hslash }^2{\rho }_P)+1]$). We consider a fast oscillation regime of “spintessence” where the equations of the problem can be simplified. We study all possible cases with arbitrary (positive and negative) values of the polytropic constant and polytropic index. The $\mathrm{\Lambda }\mathrm{CDM}$ model, the Chaplygin gas model, and the Bose-Einstein condensate model are recovered as particular cases of our study corresponding to a constant potential ($\gamma =0$), an inverse square-law potential ($\gamma =-1$), and a quartic potential ($\gamma =2$). We also derive the two-fluid representation of the Chaplygin gas model.