We study the retarded field sourced by a uniformly accelerated particle in a nonlocal scalar field theory. While the presence of nonlocality regularizes the field at the location of the source, we also show that Lorentz-invariant nonlocal field theories are particularly sensitive to the somewhat unphysical assumption of uniform acceleration, leading to logarithmic divergences on the acceleration horizon. Analytic properties of the nonlocal retarded Green function indicate that the divergences can be removed by placing appropriate sources on the acceleration horizon in the asymptotic past.

Solutions to the backreaction equation in $1+1$-dimensional semiclassical electrodynamics are obtained and analyzed when considering a time-varying homogeneous electric field initially generated by a classical electric current, coupled to either a quantized scalar field or a quantized spin-$\frac{1}{2}$ field. Particle production by way of the Schwinger effect leads to backreaction effects that modulate the electric field strength. Details of the particle production process are investigated along with the transfer of energy between the electric field and the particles. The validity of the semiclassical approximation is also investigated using a criterion previously implemented for chaotic inflation and, in an earlier form, semiclassical gravity. The criterion states that the semiclassical approximation will break down if any linearized gauge-invariant quantity constructed from solutions to the linear response equation, with finite nonsingular data, grows rapidly for some period of time. Approximations to homogeneous solutions of the linear response equation are computed and it is found that the criterion is violated when the maximum value, $E_{\max }$, obtained by the electric field is of the order of the critical scale for the Schwinger effect, $E_{\max }\sim E_{\mathrm{crit}}\equiv m^2/q$, where $m$ is the mass of the quantized field and $q$ is its electric charge. For these approximate solutions the criterion appears to be satisfied in the extreme limits $\frac{q{E}_{\max }}{m^2}\ll 1$ and $\frac{q{E}_{\max }}{m^2}\gg 1$.

We revisit the system consisting of a neutron star that harbors a small, possibly primordial, black hole at its center, focusing on a nonspinning black hole embedded in a nonrotating neutron star. Extending earlier treatments, we provide an analytical treatment describing the rate of secular accretion of the neutron star matter onto the black hole, adopting the relativistic Bondi accretion formalism for stiff equations of state that we presented elsewhere. We use these accretion rates to sketch the evolution of the system analytically until the neutron star is completely consumed. We also perform numerical simulations in full general relativity for black holes with masses up to nine orders of magnitude smaller than the neutron star mass, including a simulation of the entire evolution through collapse for the largest black hole mass. We construct relativistic initial data for these simulations by generalizing the black hole puncture method to allow for the presence of matter, and evolve these data with a code that is optimally designed to resolve the vastly different length scales present in this problem. We compare our analytic and numerical results, and provide expressions for the lifetime of neutron stars harboring such endoparasitic black holes.

In the Einstein-Cartan framework the torsion-free conditions arise within the Hamiltonian treatment as second-class constraints. The standard strategy is to solve these constraints, eliminating the torsion from the classical theory, before quantization. Here we advocate leaving the torsion inside the other constraints before quantization, leading at first to wave functions that can be called “kinematical” with regards to the torsion, but not the other constraints. The torsion-free condition can then be imposed as a condition upon the physical wave packets one constructs, satisfying the usual uncertainty relations, and so with room for quantum fluctuations in the torsion. This alternative strategy has the surprising effect of clarifying the sense in which the wave functions solving an explicitly real theory are “delta-function normalizable.” Such solutions with zero (or any fixed) torsion, should be interpreted as plane waves in torsion space. Properly constructed wave packets are therefore normalizable in the standard sense. Given that they are canonical duals, this statement applies equally well to the Chern-Simons state (connection representation) and the Hartle-Hawking wave function (metric representation). We show how, when torsion is taken into account, the Hartle-Hawking wave function is replaced by a Gauss-Airy function, with finite norm, which we call the Hartle-Hawking beam. The Chern-Simons state, instead, becomes a packet with a Gaussian probability distribution in connection space. We conclude the paper with two sections explaining how to generalize these results beyond minisuperspace.

Hořava gravity is a proposal for completing general relativity in the ultraviolet by interactions that violate Lorentz invariance at very high energies. We focus on ($2+1$)-dimensional projectable Hořava gravity, a theory which is renormalizable and perturbatively ultraviolet-complete, enjoying an asymptotically free ultraviolet fixed point. Adding a small cosmological constant to regulate the long-distance behavior of the metric, we search for all circularly symmetric stationary vacuum solutions with vanishing angular momentum and approaching the de Sitter metric with a possible angle deficit at infinity. We find a two-parameter family of such geometries. Apart from the cosmological de Sitter horizon, these solutions generally contain another Killing horizon and should therefore be interpreted as black holes from the viewpoint of the low-energy theory. Contrary to naive expectations, their central singularity is not resolved by the higher derivative terms present in the action. It is unknown at present if these solutions form as a result of gravitational collapse. The only solution regular everywhere is just the de Sitter metric devoid of any black hole horizon.

The radiation of linear momentum imparts a recoil (or “kick”) to the center of mass of a merging black-hole binary system. Recent numerical relativity calculations have shown that eccentricity can lead to an approximate 25% increase in recoil velocities for equal-mass, spinning binaries with spins lying in the orbital plane (“superkick” configurations) [U. Sperhake et al. Phys. Rev. D 101, 024044 (2020)]. Here we investigate the impact of nonzero eccentricity on the kick magnitude and gravitational-wave emission of nonspinning, unequal-mass black hole binaries. We confirm that nonzero eccentricities at merger can lead to kicks which are larger by up to $\sim 25\%$ relative to the quasicircular case. We also find that the kick velocity $v$ has an oscillatory dependence on eccentricity, which we interpret as a consequence of changes in the angle between the infall direction at merger and the apoapsis (or periapsis) direction.

In the post-detection era of gravitational wave (GW) astronomy, core collapse supernovae (CCSN) are one of the most interesting potential sources of signals arriving at the Advanced LIGO detectors. Mukherjee et al. have developed and implemented a new method to search for GW signals from the CCSN search based on a multistage, high accuracy spectral estimation to effectively achieve higher detection signal to noise ratio (SNR). The study has been further enhanced by incorporation of a convolutional neural network (CNN) to significantly reduce false alarm rates (FAR). The combined pipeline is termed multilayer signal estimation (MuLaSE) that works in an integrative manner with the coherent wave burst (cWB) pipeline. In order to compare the performance of this new search pipeline, termed “MuLaSECC”, with the cWB, an extensive analysis has been performed with two families of core collapse supernova waveforms corresponding to two different three dimensional (3D) general relativistic CCSN explosion models, viz. Kuroda 2017 and the Ott 2013. The performance of this pipeline has been characterized through receiver operating characteristics (ROC) and the reconstruction of the detected signals. The MuLaSECC is found to have higher efficiency in low false alarm range, a higher detection probability of weak signals and an improved reconstruction, especially in the lower frequency domain.

We investigate the use of parabolic equation (PE) methods for solving radio-wave propagation in polar ice. PE methods provide an approximate solution to Maxwell’s equations, in contrast to full-field solutions such as finite-difference-time-domain (FDTD) methods, yet provide a more complete model of propagation than simple geometric ray-tracing (RT) methods that are the current state of the art for simulating in-ice radio detection of neutrino-induced cascades. PEs are more computationally efficient than FDTD methods, and more flexible than RT methods, allowing for the inclusion of diffractive effects and modeling of propagation in regions that cannot be modeled with geometric methods. We present a new PE approximation suited to the in-ice case. We conclude that current ray-tracing methods may be too simplistic in their treatment of ice properties, and their continued use could overestimate experimental sensitivity for in-ice neutrino detection experiments. We discuss the implications for current in-ice Askaryan-type detectors and for the upcoming Radar Echo Telescope, two families of experiments for which these results are most relevant. We suggest that PE methods be investigated further for in-ice radio applications.

Solar flares convert magnetic energy into thermal and nonthermal plasma energy, the latter implying particle acceleration of charged particles such as protons. Protons are injected out of the coronal acceleration region and can interact with dense plasma in the lower solar atmosphere, producing mesons that subsequently decay into gamma rays and neutrinos at $\mathcal{O}(\mathrm{MeV}\text{−}\mathrm{GeV})$ energies. We present the results of the first search for GeV neutrinos emitted during solar flares carried out with the IceCube Neutrino Observatory. While the experiment was originally designed to detect neutrinos with energies between 10 GeV and a few PeV, a new approach allowing for a $\mathcal{O}(\mathrm{GeV})$ energy threshold will be presented. The resulting limits allow us to constrain some of the theoretical estimates of the expected neutrino flux.

The Breit-Wheeler pair production process in $2+1$ dimensional spacetime is investigated. In the perturbative regime, nonvanishing rates at the energy threshold are found when odd numbers of photons take part in the reaction. This behavior is understood as a direct consequence of the reduced dimensionality and resembles a corresponding prediction made in gapped graphene monolayers. In the nonperturbative strong field regime, the effect of the dimensionality manifests itself in a different rate dependence on the quantum nonlinearity parameter. The consequence of this deviation is discussed briefly in line with the applicability of perturbation theory. We argue that, in addition to large values of the quantum nonlinearity parameter, the super-renormalizable character of quantum electrodynamics in $2+1$ dimensional spacetime might give rise to a breakdown of perturbation theory within certain energy scales.

In this paper, we apply the Goldstone equivalence gauge to calculate the $1\leftrightarrow 2$ processes of a sterile neutrino in a thermal plasma below the standard model (SM) critical temperature $T_c\approx 160\mathrm{GeV}$. The sterile neutrino’s mass is around the electroweak scale, $50\mathrm{GeV}\le m_N\le 200\mathrm{GeV}$, and the acquired thermal averaged effective width ${\overline{\mathrm{\Gamma }}}_{\mathrm{tot}}$ does not depend on the gauge selection and is continuous around the crossover. We also apply our results to perform a preliminary calculation of leptogenesis.

While the QCD axion is often considered to be necessarily light ($\lesssim \mathrm{eV}$), recent work has opened a viable and interesting parameter space for heavy axions, which solve both the strong $CP$ and the axion quality problems. These well-motivated heavy axions, as well as the generic axionlike particles, call for explorations in the GeV mass realm at collider and beam dump environments. The primary upcoming neutrino experiment, Deep Underground Neutrino Experiment, is simultaneously also a powerful beam dump experiment, enabled by its multipurpose near detector complex. In this study, we show with detailed analyses that the Deep Underground Neutrino Experiment near detector has a unique sensitivity to heavy axions for masses between 20 MeV and 2 GeV, complementary to other future experiments.

We perform a feasibility study to search for axionlike particles (ALPs) using vector boson fusion (VBF) processes at the LHC. We work in an effective field theory framework with a cutoff scale $\mathrm{\Lambda }$ and ALP mass $m_a$, and assume that ALPs couple to photons with strength $\propto 1/\mathrm{\Lambda }$. Assuming proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$, we present the total VBF ALP production cross sections, ALP decay widths and lifetimes, and relevant kinematic distributions as a function of $m_a$ and $\mathrm{\Lambda }$. We consider the $a\to \gamma \gamma$ decay mode to show that the requirement of an energetic diphoton pair combined with two forward jets with large dijet mass and pseudorapidity separation can significantly reduce the Standard Model backgrounds, leading to a $5\sigma$ discovery reach for $10\mathrm{MeV}\lesssim m_a\lesssim 1\mathrm{TeV}$ with $\mathrm{\Lambda }\lesssim 2\mathrm{TeV}$, assuming an integrated luminosity of $3000{\mathrm{fb}}^{-1}$. In particular, this extends the LHC sensitivity to a previously unstudied region of the ALP parameter space.

We study the processes $e^{+}{e}^{-}\to 2({\pi }^{+}{\pi }^{-}){\pi }^0{\pi }^0{\pi }^0\gamma$ and $2({\pi }^{+}{\pi }^{-}){\pi }^0{\pi }^0\eta \gamma$ in which an energetic photon is radiated from the initial state. The data were collected with the BABAR detector at SLAC. About 14 000 and 4700 events, respectively, are selected from a data sample corresponding to an integrated luminosity of $469{\mathrm{fb}}^{-1}$. The invariant mass of the hadronic final state defines the effective $e^{+}{e}^{-}$ center-of-mass energy. The center-of-mass energies range from threshold to 4.5 GeV. From the mass spectra, the first ever measurements of the $e^{+}{e}^{-}\to 2({\pi }^{+}{\pi }^{-}){\pi }^0{\pi }^0{\pi }^0$ and the $e^{+}{e}^{-}\to 2({\pi }^{+}{\pi }^{-}){\pi }^0{\pi }^0\eta$ cross sections are performed. The contributions from $\omega {\pi }^{+}{\pi }^{-}{\pi }^0{\pi }^0$, $\eta 2({\pi }^{+}{\pi }^{-})$, and other intermediate states are presented. We observe the $J/\psi$ and $\psi (2S)$ in most of these final states and measure the corresponding branching fractions, many of them for the first time.

We consider cosmological models where dark matter is universally charged under a dark Abelian gauge field. This new interaction is repulsive and competes with gravity on large scales and in the dynamics of galaxies and clusters. We focus on nonlinear models of dark electrodynamics where the effects of the new force are screened within a K-mouflage radius that helps avoiding traditional constraints on charged dark matter models. We discuss the background cosmology of these models in a Newtonian approach and show the equivalence with relativistic Lemaître models where an inhomogeneous pressure due to the electrostatic interaction is present. In particular, after foliating the Universe using spherical shells, we find that dark matter shells with initially different radii do not evolve similarly as they exit their K-mouflage radii at different times, resulting in a breaking of the initial comoving evolution. In the large time regime, the background cosmology is described by a comoving but inhomogeneous model with a reduced gravitational Newton constant and a negative curvature originating from the electrostatic pressure. In this model, baryons do not directly feel the electrostatic interaction, but are influenced by the inhomogeneous matter distribution induced by the electric force. We find that shells of smaller radii evolve faster than the outer shells which feel the repulsive interaction earlier. This mimics the discrepancy between the large scale Hubble rate and the local one. Similarly, as galaxies and clusters are not screened by the new interaction, large scale global flows would result from the existence of the new dark electromagnetic interaction.

Conventional algorithms for galaxy power-spectrum estimation measure the true spectrum convolved with a survey window function, which, for parameter inference, must be compared with a similarly convolved theory model. In this work, we directly estimate the unwindowed power spectrum multipoles using quadratic estimators akin to those introduced in the late 1990s. Under Gaussian assumptions, these are optimal and free from the leading-order effects of pixelization and non-Poissonian shot noise. They may be straightforwardly computed given the survey dataset and a suite of simulations of known cosmology. We implement the pixel-based maximum-likelihood estimator and a simplification based on the Feldman-Kaiser-Peacock weighting scheme, both of which can be computed via FFTs and conjugate-gradient descent methods. Furthermore, the estimators allow direct computation of spectrum coefficients in an arbitrary linear compression scheme, without needing to first bin the statistic. Applying the technique to a subset of the BOSS DR12 galaxies, we find that the pixel-based quadratic estimators give statistically consistent power spectra, compressed coefficients, and cosmological parameters to those obtained with the usual windowed approaches. Because of the sample’s low number density and compact window function, the optimal weighting scheme gives little improvement over the simplified form; this may change for dense surveys or those focusing on primordial non-Gaussianity. The technique is shown to be efficient and robust, and shows significant potential for measuring the windowless power spectrum and bispectrum in the presence of weak non-Gaussianity.

We present a novel method for sampling iso-likelihood contours in nested sampling using a type of machine learning algorithm known as normalizing flows and incorporate it into our sampler nessai. nessai is designed for problems where computing the likelihood is computationally expensive and therefore the cost of training a normalizing flow is offset by the overall reduction in the number of likelihood evaluations. We validate our sampler on 128 simulated gravitational wave signals from compact binary coalescence and show that it produces unbiased estimates of the system parameters. Subsequently, we compare our results to those obtained with dynesty and find good agreement between the computed log-evidences while requiring 2.07 times fewer likelihood evaluations. We also highlight how the likelihood evaluation can be parallelized in nessai without any modifications to the algorithm. Finally, we outline diagnostics included in nessai and how these can be used to tune the sampler’s settings.

Observed thermal emission from accreting neutron stars (NSs) in a quiescent state is believed to be powered by nonequilibrium nuclear reactions that heat the stellar crust (deep crustal heating paradigm). We derive a simple universal formula for the heating efficiency, assuming that an NS has a fully accreted crust. We further show that, within the recently proposed thermodynamically consistent approach to the accreted crust, the heat release can be parametrized by only one parameter—the pressure $P_{\mathrm{oi}}$ at the outer-inner crust interface (as we argue, this pressure should not necessarily coincide with the neutron-drip pressure). We discuss possible values of $P_{\mathrm{oi}}$ for a selection of nuclear models that account for shell effects, and we determine the net heat release and its distribution in the crust as a function of $P_{\mathrm{oi}}$. We conclude that the heat release should be reduced by a factor of few in comparison to previous works.

The physics reach of a low threshold (100 eV) scintillating argon bubble chamber sensitive to coherent elastic neutrino-nucleus scattering ($\mathrm{CE}\nu \mathrm{NS}$) from reactor neutrinos is studied. The sensitivity to the weak mixing angle, neutrino magnetic moment, and a light $Z^{\prime }$ gauge boson mediator are analyzed. A Monte Carlo simulation of the backgrounds is performed to assess their contribution to the signal. The analysis shows that world-leading sensitivities are achieved with a one-year exposure for a 10 kg chamber at 3 m from a $1{\mathrm{MW}}_{th}$ research reactor or a 100 kg chamber at 30 m from a $2000{\mathrm{MW}}_{th}$ power reactor. Such a detector has the potential to become the leading technology to study $\mathrm{CE}\nu \mathrm{NS}$ using nuclear reactors.

We report on a new class of flux vacua generically present in Calabi-Yau compactifications of type-IIB string theory. At these vacua, the mass spectrum of the complete axiodilaton/complex structure sector is given, to leading order in ${\alpha }^{\prime }$ and $g_s$, by a simple analytic formula independent of the choice of Calabi-Yau. We provide a method to find these vacua and construct an ensemble of 17,054 solutions for the Calabi-Yau hypersurface ${\mathbb{WP}}_{[1,1,1,6,9]}^4$, where the masses of the axiodilaton and the 272 complex structure fields can be explicitly computed.