We investigate a new method to recover (if any) a possible varying speed of light (VSL) signal from cosmological data. It comes as an upgrade by Salzano, Dąbrowski, and Lazkoz [Phys. Rev. Lett.114, 101304 (2015); Phys. Rev. D 93, 063521 (2016)], where it was argued that such a signal could be detected at a single redshift location only. Here, we show how it is possible to extract information on a VSL signal on an extended redshift range. We use mock cosmological data from future galaxy surveys (BOSS, DESI, WFirst-2.4 and SKA): the sound horizon at decoupling imprinted in the clustering of galaxies (baryon acoustic oscillations) as an angular diameter distance, and the expansion rate derived from those galaxies recognized as cosmic chronometers. We find that, given the forecast sensitivities of such surveys, a $\sim 1\%$ VSL signal can be detected at $3\sigma$ confidence level in the redshift interval $z\in [0.,1.55]$. Smaller signals ($\sim 0.1\%$) will be hardly detected (even if some lower possibility for a $1\sigma$ detection is still possible). Finally, we discuss the degeneration between a VSL signal and a non-null spatial curvature; we show that, given present bounds on curvature, any signal, if detected, can be attributed to a VSL signal with a very high confidence. On the other hand, our method turns out to be useful even in the classical scenario of a constant speed of light: in this case, the signal we reconstruct can be totally ascribed to spatial curvature and, thus, we might have a method to detect a 0.01-order curvature in the same redshift range with a very high confidence.

Astrophysical black hole candidates, although long thought to have a horizon, could be horizonless ultracompact objects. This intriguing possibility is motivated by the black hole information paradox and a plausible fundamental connection with quantum gravity. Asymptotically free quadratic gravity is considered here as the UV completion of general relativity. A classical theory that captures its main features is used to search for solutions as sourced by matter. We find that sufficiently dense matter produces a novel horizonless configuration, the 2-2-hole, which closely matches the exterior Schwarzschild solution down to about a Planck proper length of the would-be horizon. The 2-2-hole is characterized by an interior with a shrinking volume and a seemingly innocuous timelike curvature singularity. The interior also has a novel scaling behavior with respect to the physical mass of the 2-2-hole. This leads to an extremely deep gravitational potential in which particles get efficiently trapped via collisions. As a generic static solution, the 2-2-hole may then be the nearly black end point of gravitational collapse. There is a considerable time delay for external probes of the 2-2-hole interior, and this determines the spacing of echoes in a postmerger gravitational wave signal.

In the first paper of this series, we proposed a novel method to probe large–scale intergalactic magnetic fields during the cosmic Dark Ages, using 21–cm tomography. This method relies on the effect of spin alignment of hydrogen atoms in a cosmological setting, and on the effect of magnetic precession of the atoms on the statistics of the 21-cm brightness-temperature fluctuations. In this paper, we forecast the sensitivity of future tomographic surveys to detecting magnetic fields using this method. For this purpose, we develop a minimum-variance estimator formalism to capture the characteristic anisotropy signal using the two-point statistics of the brightness-temperature fluctuations. We find that, depending on the reionization history, and subject to the control of systematics from foreground subtraction, an array of dipole antennas in a compact-grid configuration with a collecting area slightly exceeding one square kilometer can achieve a $1\sigma$ detection of $\sim {10}^{-21}\mathrm{Gauss}$ comoving (scaled to present-day value) within three years of observation. Using this method, tomographic 21–cm surveys could thus probe ten orders of magnitude below current cosmic microwave background constraints on primordial magnetic fields, and provide exquisite sensitivity to large-scale magnetic fields in situ at high redshift.

We propose a method of measuring extremely weak magnetic fields in the intergalactic medium prior to and during the epoch of cosmic reionization. The method utilizes the Larmor precession of spin-polarized neutral hydrogen in the triplet state of the hyperfine transition. This precession leads to a systematic change in the brightness temperature fluctuations of the 21-cm line from the high-redshift universe, and thus the statistics of these fluctuations encode information about the magnetic field the atoms are immersed in. The method is most suited to probing fields that are coherent on large scales; in this paper, we consider a homogenous magnetic field over the scale of the 21-cm fluctuations. Due to the long lifetime of the triplet state of the 21-cm transition, this technique is naturally sensitive to extremely weak field strengths, of order ${10}^{-19}\mathrm{G}$ at a reference redshift of $\sim 20$ (or ${10}^{-21}\mathrm{G}$ if scaled to the present day). Therefore, this might open up the possibility of probing primordial magnetic fields just prior to reionization. If the magnetic fields are much stronger, it is still possible to use this method to infer their direction, and place a lower limit on their strength. In this paper (Paper I in a series on this effect), we perform detailed calculations of the microphysics behind this effect, and take into account all the processes that affect the hyperfine transition, including radiative decays, collisions, and optical pumping by Lyman-$\alpha$ photons. We conclude with an analytic formula for the brightness temperature of linear-regime fluctuations in the presence of a magnetic field, and discuss its limiting behavior for weak and strong fields.

The announcement by the IceCube Collaboration of the observation of 53 astrophysical neutrino candidates in the energy range $0.03\lesssim E_{\nu }/\mathrm{PeV}\lesssim 2$ has been greeted with a great deal of justified excitement. Herein we provide fits of single and a broken power-law energy-spectra to these high-energy starting events (HESEs). By comparing our statistical results from fits to (background-free) shower HESE data with the spectral shape of muon neutrinos recently reported by the IceCube Collaboration, we show that there is ($3\sigma$) evidence for a break in the spectrum of astrophysical neutrinos. After that we use the fitted result to predict the rate of Glashow events (in the $\approx 6.3\mathrm{PeV}$ region) and double-bang tau neutrino events (in the PeV region) just at the threshold of IceCube detection.

We present a measurement of the cosmic-ray $\mathrm{electron}+\mathrm{positron}$ spectrum between 7 GeV and 2 TeV performed with almost seven years of data collected with the Fermi Large Area Telescope. We find that the spectrum is well fit by a broken power law with a break energy at about 50 GeV. Above 50 GeV, the spectrum is well described by a single power law with a spectral index of $3.07\pm 0.02(\mathrm{stat}+\mathrm{syst})\pm 0.04(\text{energy measurement})$. An exponential cutoff lower than 1.8 TeV is excluded at 95% CL.

We use a locally constant field approximation (LCFA) to study the one-loop Heisenberg-Euler effective action in a particular class of slowly varying inhomogeneous electric fields of Lorentzian shape with $0\le d<4$ inhomogeneous directions. We show that, for these fields, the LCFA of the Heisenberg-Euler effective action can be represented in terms of a single parameter integral, with the constant field effective Lagrangian with rescaled argument as integration kernel. The imaginary part of the Heisenberg-Euler effective action contains information about the instability of the quantum vacuum towards the formation of a state with real electrons and positrons. Here, in particular, we focus on the dependence of the instantaneous vacuum decay rate on the dimension $d$ of the field inhomogeneity. Specifically, for weak fields, we find an overall parametric suppression of the effect with $(E_0/E_{\mathrm{cr}}{)}^{d/2}$, where $E_0$ is the peak field strength of the inhomogeneity and $E_{\mathrm{cr}}$ the critical electric field strength.

The group $\mathrm{\Sigma }(36\times 3)$ with the generalized $CP$ transformation is introduced to predict the mixing pattern of leptons. Various combinations of Abelian residual flavor symmetries with $CP$ transformations are surveyed. Six mixing patterns could accommodate the fit data of neutrinos oscillation at the $3\sigma$ level. Among them, two patterns predict the nontrivial Dirac $CP$ phase, around $\pm 57°$ or $\pm 123°$, which is in accordance with the result of the literature and the recent fit data. Furthermore, one pattern could satisfy the experimental constraints at the $1\sigma$ level.

Nonperturbative methods have been well developed for QED with the so-called $t$-electric potential steps. In this case a calculation technique is based on the existence of specific exact solutions (in and out solutions) of the Dirac equation. However, there are only few cases when such solutions are known. Here, we demonstrate that for $t$-electric potential steps slowly varying with time there exist physically reasonable approximations that maintain the nonperturbative character of QED calculations even in the absence of the exact solutions. Defining the slowly varying regime in general terms, we can observe a universal character of vacuum effects caused by a strong electric field. In the present article, we find universal approximate representations for the total density of created pairs and vacuum mean values of the current density and energy-momentum tensor that hold true for arbitrary $t$-electric potential steps slowly varying with time. These representations do not require knowledge of the corresponding solutions of the Dirac equation; they have a form of simple functionals of a given slowly varying electric field. We establish relations of these representations with leading terms of the derivative expansion approximation. These results allow one to formulate some semiclassical approximations that are not restricted by the smallness of differential mean numbers of created pairs.

In this paper we study the lepton flavor violating $Z$ boson decays $Z\to \tau \mu$ and $Z\to \tau e$ in the context of low scale seesaw models with new heavy Majorana neutrinos whose masses could be reachable at the LHC. Our computations of the decay rates are done in the particular realization given by the inverse seesaw model with six extra heavy neutrinos which are quasidegenerate in three pseudo-Dirac pairs. In particular, we focus on scenarios that are built ad hoc to produce suppressed rates in all the processes involving $\mu \text{−}e$ transitions, given the fact that these are by far the most strongly constrained by present data. We will fully explore the $Z\to \tau \mu$ and $Z\to \tau e$ rates, together with a set of observables that we find to be the most constraining ones, and we will conclude that sizable rates of up to $2\times {10}^{-7}$, accessible at future colliders, can be reached in this model for Majorana masses in the few TeV range, potentially reachable at LHC.

Parametrizations of the pp scattering data at the LHC collision energies indicate a hollow in the inelasticity profile of the pp interaction, with less absorption for head-on collisions than at a nonzero impact parameter. We show that some qualitatively unnoticed features may be unveiled by a judicious application of the inverse scattering problem in the eikonal approximation and interpretation within an optical potential model. The hollowness effect is magnified in a 3D picture of the optical potential, and will presumably be enhanced at yet higher energies. Moreover, in 3D it sets in at much smaller energies than at the LHC. We argue that hollowness in the impact parameter is a quantum effect, relying on the build-up of the real part of the eikonal scattering phase and its possible passage through $\pi /2$. We also show that it precludes models of inelastic collisions where inelasticity is obtained by naive folding of partonic densities.

The covariant propagator of a fermion with intrinsic magnetic moment interacting with a uniform external magnetic field is presented for finite temperature and baryonic density. The case of a scalar boson is also considered. The final expressions are given in terms of a four-dimensional momentum representation. These results, which take account of the full effect of the magnetic field, are used to evaluate the modification of the pion mass at zero temperature as a function of the density and the magnetic intensity. For this purpose a self-consistent calculation, including one- and two-pion vertices, is employed.

We investigate the Wigner distributions for $u$ and $d$ quarks in a light-front quark-diquark model of a proton to unravel the spatial and spin structure. The light-front wave functions are modeled from the soft-wall AdS/QCD prediction. We consider the contributions from both the scalar and the axial vector diquarks. The Wigner distributions for unpolarized, longitudinally polarized, and transversely polarized protons are presented in the transverse momentum plane as well as in the transverse impact parameter plane. The Wigner distributions satisfy a Soffer-bound-type inequality. We also evaluate all the leading-twist GTMDs and show their scale evolution. The spin-spin correlations between the quark and the proton are investigated.

Assuming only statistical mechanics and general relativity, we calculate the maximal temperature of gas of particles placed in anti–de Sitter (AdS) spacetime. If two particles with a given center of mass energy come close enough, according to classical gravity, they will form a black hole. We focus only on the black holes with a Hawking temperature lower than the environment, because they do not disappear. The number density of such black holes grows with the temperature in the system. At a certain finite temperature, the thermodynamical system will be dominated by black holes. This critical temperature is lower than the Planck temperature for the values of the AdS vacuum energy density below the Planck density. This result might be interesting from the AdS/CFT correspondence point of view, since it is different from the Hawking-Page phase transition, and it is not immediately clear what effect dynamically limits the maximal temperature of the thermal state on the CFT side of the correspondence.

Spacetime nonmetricity can be studied experimentally through its couplings to fermions and photons. We use recent high-precision searches for Lorentz violation to deduce first constraints involving the 40 independent nonmetricity components down to levels of order ${10}^{-43}\mathrm{GeV}$.

Measurements of neutrino mass in cosmological observations rely on two-point statistics that are hindered by significant degeneracies with the optical depth and galaxy bias. The relative velocity effect between cold dark matter and neutrinos induces a large scale dipole in the matter density field and may be able to provide orthogonal constraints to standard techniques. We numerically investigate this dipole in the TianNu simulation, which contains cold dark matter and 50 meV neutrinos. We first compute the dipole using a new linear response technique where we treat the displacement caused by the relative velocity as a phase in Fourier space and then integrate the matter power spectrum over redshift. Then, we compute the dipole numerically in real space using the simulation density and velocity fields. We find excellent agreement between the linear response and N-body methods. Utilizing the dipole as an observational tool requires two tracers of the matter distribution that are differently biased with respect to the neutrino density.

We study flat Friedmann-Lemaître-Robertson-Walker $\alpha$-attractor E- and T-models by introducing a dynamical systems framework that yields regularized unconstrained field equations on two-dimensional compact state spaces. This results in both illustrative figures and a complete description of the entire solution spaces of these models, including asymptotics. In particular, it is shown that observational viability, which requires a sufficient number of $e$-folds, is associated with a particular solution given by a one-dimensional center manifold of a past asymptotic de Sitter state, where the center manifold structure also explains why nearby solutions are attracted to this “inflationary attractor solution.” A center manifold expansion yields a description of the inflationary regime with arbitrary analytic accuracy, where the slow-roll approximation asymptotically describes the tangency condition of the center manifold at the asymptotic de Sitter state.