Motivated by recent developments in black hole thermodynamics, we investigate van der Waals phase transitions of charged black holes in massive gravity. We find that massive gravity theories can exhibit strikingly different thermodynamic behavior compared to that of Einstein gravity, and that the mass of the graviton can generate a range of new phase transitions for topological black holes that are otherwise forbidden.

We study the flavor structure in $SO(32)$ heterotic string theory on six-dimensional tori with magnetic fluxes. Specifically, we focus on models with the flavor symmetries $SU(3{)}_f$ and $\mathrm{\Delta }(27)$. In both models, we can realize the realistic quark masses and mixing angles.

We revisit certain aspects of thermalization in 2D conformal field theory (CFT). In particular, we consider similarities and differences between the time dependence of correlation functions in various states in rational and non-rational CFTs. We also consider the distinction between global and local thermalization and explain how states obtained by acting with a diffeomorphism on the ground state can appear locally thermal, and we review why the time-dependent expectation value of the energy-momentum tensor is generally a poor diagnostic of global thermalization. Since all 2D CFTs have an infinite set of commuting conserved charges, generic initial states might be expected to give rise to a generalized Gibbs ensemble rather than a pure thermal ensemble at late times. We construct the holographic dual of the generalized Gibbs ensemble and show that, to leading order, it is still described by a Banados-Teitelboim-Zanelli black hole. The extra conserved charges, while rendering $c<1$ theories essentially integrable, therefore seem to have little effect on large-$c$ conformal field theories.

We show explicitly that the full structure of IIB string theory is needed to remove the nonlocalities that arise in boundary conformal theories that border hyperbolic spaces on ${\mathrm{AdS}}_5$. Specifically, using the Caffarelli/Silvestri [1], Graham/Zworski [2], and Chang/Gonzalez [3] extension theorems, we prove that the boundary operator conjugate to bulk p-forms with negative mass in geodesically complete metrics is inherently a nonlocal operator, specifically the fractional conformal Laplacian. The nonlocality, which arises even in compact spaces, applies to any degree p-form such as a gauge field. We show that the boundary theory contains fractional derivatives of the longitudinal components of the gauge field if the gauge field in the bulk along the holographic direction acquires a mass via the Higgs mechanism. The nonlocality is shown to vanish once the metric becomes incomplete, for example, either (1) asymptotically by adding N transversely stacked Dd-branes or (2) exactly by giving the boundary a brane structure and including a single transverse Dd-brane in the bulk. The original Maldacena conjecture within IIB string theory corresponds to the former. In either of these proposals, the location of the Dd-branes places an upper bound on the entanglement entropy because the minimal bulk surface in the AdS reduction is ill-defined at a brane interface. Since the brane singularities can be circumvented in the full 10-dimensional spacetime, we conjecture that the true entanglement entropy must be computed from the minimal surface in 10-dimensions, which is of course not minimal in the ${\mathrm{AdS}}_5$ reduction.

Lorentz symmetry violations can be described by an effective field theory framework that contains both general relativity and the Standard Model of particle physics called the Standard Model extension (SME). Recently, postfit analysis of Gravity Probe B and binary pulsars led to an upper limit at the ${10}^{-4}$ level on the time-time coefficient ${\overline{s}}^{TT}$ of the pure-gravity sector of the minimal SME. In this work, we derive the observable of very long baseline interferometry (VLBI) in SME and then implement it into a real data analysis code of geodetic VLBI observations. Analyzing all available observations recorded since 1979, we compare estimates of ${\overline{s}}^{TT}$ and errors obtained with various analysis schemes, including global estimations over several time spans, and with various Sun elongation cutoff angles, and by analysis of radio source coordinate time series. We obtain a constraint on ${\overline{s}}^{TT}=(-5\pm 8)\times {10}^{-5}$, directly fitted to the observations and improving by a factor of 5 previous postfit analysis estimates.

The scattering equations give striking formulas for massless scattering amplitudes at tree level and, as shown recently, at one loop. The progress at loop level was based on ambitwistor-string theory, which naturally yields the scattering equations. We proposed that, for ambitwistor strings, the standard loop expansion in terms of the genus of the world sheet is equivalent to an expansion in terms of nodes of a Riemann sphere, with the nodes carrying the loop momenta. In this paper, we show how to obtain two-loop scattering equations with the correct factorization properties. We adapt genus-two integrands from the ambitwistor string to the nodal Riemann sphere and show that these yield correct answers, by matching standard results for the four-point two-loop amplitudes of maximal supergravity and super-Yang-Mills theory. In the Yang-Mills case, this requires the loop analogue of the Parke-Taylor factor carrying the color dependence, which includes nonplanar contributions.

We renormalize the $SU(N)$ Gross-Neveu model in the modified minimal subtraction scheme at four loops and determine the $\beta$ function at this order. The theory ceases to be multiplicatively renormalizable when dimensionally regularized due to the generation of evanescent 4-Fermi operators. The first of these appears at three loops and we correctly take their effect into account in deriving the renormalization group functions. We use the results to provide estimates of critical exponents relevant to phase transitions in graphene.

In this paper we investigate a particular ghost-free bimetric theory that exhibits the partially massless (PM) symmetry at quadratic order. At this order the global $SO(1,4)$ symmetry of the theory is enhanced to $SO(1,5)$. We show that this global symmetry becomes inconsistent at cubic order, in agreement with a previous calculation. Furthermore, we find that the PM symmetry of this theory cannot be extended beyond cubic order in the PM field. More importantly, it is shown that the PM symmetry cannot be extended to quartic order in any theory with one massless and one massive spin-2 fields.

In this paper, we investigate the stability of the flat Friedmann-Lemaitre-Robertson-Walker metric in $f(T)$ gravity. This is achieved by analyzing the small perturbations, $\delta$ about the Hubble parameter and the matter energy density, ${\delta }_{\mathrm{m}}$. We find that $\delta \propto \dot{H}/H$ and ${\delta }_{\mathrm{m}}\propto H$. Since the Hubble parameter depends on the function $f(T)$, two models were considered (A) the power-law model $f(T)=\alpha (-T{)}^n$, and (B) the exponential model $f(T)=\alpha T_0(1-\exp [-p\sqrt{\frac{T}{T_0}}])$, where the parameters $n$ and $p$ were chosen to give comparable physical results. For the parameters considered, it was found that the solutions are stable with vanishing $\delta$ and decaying then constant ${\delta }_{\mathrm{m}}$, meaning that the matter perturbations persist during late times.

We investigate the late-time tail of the retarded Green function for the dynamics of a linear field perturbation of Kerr spacetime. We develop an analytical formalism for obtaining the late-time tail to arbitrary order for general integer spin of the field. We then apply this formalism to obtain the details of the first five orders in the late-time tail of the Green function for the case of a scalar field. To leading order we recover the known power-law tail $t^{-2\ell -3}$, and at third order we obtain a new logarithmic correction, $t^{-2\ell -5}\ln t$, where $\ell$ is the field multipole.

“Diagonal” spatially inhomogeneous (SI) models are introduced under the assumption of the existence of (proper) intrinsic symmetries and can be seen, in some sense, as complementary to the Szekeres models. The structure of this class of spacetimes can be regarded as a generalization of the (twist-free) locally rotationally symmetric geometries without any global isometry containing, however, these models as special cases. We consider geometries where a six-dimensional algebra $\mathcal{I}\mathcal{C}$ of intrinsic conformal vector fields (ICVFs) exists that acts on a two-dimensional (pseudo)-Riemannian manifold. Its members ${\mathbf{X}}_{\alpha }$—constituted of three intrinsic Killing vector fields and three proper and gradient ICVFs—and the specific form of the gravitational field are given explicitly. An interesting consequence, in contrast with the Szekeres models, is the immediate existence of conserved quantities along null geodesics. We check computationally that the magnetic part $H_{ab}$ of the Weyl tensor vanishes, whereas the shear ${\sigma }_{ab}$ and the electric part $E_{ab}$ share a common eigenframe irrespective of the fluid interpretation of the models. A side result is the fact that the spacetimes are foliated by a set of conformally flat three-dimensional timelike slices when the anisotropy of the flux-free fluid is described only in terms of the three principal inhomogeneous “pressures” $p_{\alpha }$, or equivalently when the Ricci tensor shares the same basis of eigenvectors with ${\sigma }_{ab}$ and $E_{ab}$. The conformal flatness also indicates that it is highly possible that a ten-dimensional algebra of ICVFs $\mathbf{\Xi }$ that acts on the three-dimensional timelike slices exists, enriching in that way the set of conserved quantities admitted by the SI models found in the present paper.

We continue our study on corrections from canonical quantum gravity to the power spectra of gauge-invariant inflationary scalar and tensor perturbations. A direct canonical quantization of a perturbed inflationary universe model is implemented, which leads to a Wheeler-DeWitt equation. For this equation, a semiclassical approximation is applied in order to obtain a Schrödinger equation with quantum-gravitational correction terms, from which we calculate the corrections to the power spectra. We go beyond the de Sitter case discussed earlier and analyze our model in the first slow-roll approximation, considering terms linear in the slow-roll parameters. We find that the dominant correction term from the de Sitter case, which leads to an enhancement of power on the largest scales, gets modified by terms proportional to the slow-roll parameters. A correction to the tensor-to-scalar ratio is also found at second order in the slow-roll parameters. Making use of the available experimental data, the magnitude of these quantum-gravitational corrections is estimated. Finally, the effects for the temperature anisotropies in the cosmic microwave background are qualitatively obtained.

We present novel constraints on cosmic-ray propagation in the Galaxy using the recent precise measurements of proton and helium spectra from AMS-02, together with preliminary AMS-02 data on the antiproton over proton ratio. To explore efficiently the large (up to 11-dimensional) parameter space we employ the nested-sampling algorithm as implemented in the MultiNest package, interfaced with the Galprop code to compute the model-predicted spectra. We use VOYAGER proton and helium data, sampling the local interstellar spectra, to constrain the solar modulation potential. We find that the turbulence of the Galactic magnetic field is well constrained, i.e., $\delta =0.30_{-0.02}^{+0.03}(\mathrm{stat}{)}_{-0.04}^{+0.10}(\mathrm{sys})$, with uncertainties dominated by systematic effects. Systematic uncertainties are determined checking the robustness of the results to the minimum rigidity cut used to fit the data (from 1 GV to 5 GV), to the propagation scenario (convection vs no convection), and to the uncertainties in the knowledge of the antiproton production cross section. Convection and reacceleration are found to be degenerate and not well constrained singularly when using data above 5 GV. Using data above 1 GV reacceleration is required, $v_{\mathrm{A}}=25\pm 2\mathrm{km}/\mathrm{s}$, although this value might be significantly affected by the low-energy systematic uncertainty in the solar modulation. In a forthcoming companion paper, we investigate the constraints imposed by AMS-02 measurements on lithium, boron, and carbon.

The muon component of extensive air showers (EAS) initiated by cosmic-ray particles carries information on the primary particle identity. We show that the muon content of EAS could be measured in a broad energy range from 10–100 TeV up to ultra-high-energy cosmic-ray range using wide field-of-view imaging atmospheric Cherenkov telescopes observing strongly inclined or nearly horizontal EAS from the ground of from high altitude. Cherenkov emission from muons in such EAS forms a distinct component (halo or tail) of the EAS image in the telescope camera. We show that detection of the muon signal could be used to measure composition of the cosmic-ray spectrum in the energy ranges of the knee, the ankle and of the Galactic-to-extragalactic transition. It could also be used to veto the cosmic-ray background in gamma-ray observations. This technique provides a possibility for up to 2 orders of magnitude improvement of sensitivity for $\gamma$-ray flux in the energy band above 10 PeV, compared to KASCADE-Grande, and an order-of-magnitude improvement of sensitivity in the multi-EeV energy band, compared to Pierre Auger Observatory.

We study the atomic physics and the astrophysical implications of a model in which the dark matter is the analog of hydrogen in a secluded sector. The self-interactions between dark matter particles include both elastic scatterings as well as inelastic processes due to a hyperfine transition. The self-interaction cross sections are computed by numerically solving the coupled Schrödinger equations for this system. We show that these self-interactions exhibit the right velocity dependence to explain the low dark matter density cores seen in small galaxies while being consistent with all constraints from observations of clusters of galaxies. For a viable solution, the dark hydrogen mass has to be in the 10–100 GeV range and the dark fine-structure constant has to be larger than 0.01. This range of model parameters requires the existence of a dark matter–antimatter asymmetry in the early universe to set the relic abundance of dark matter. For this range of parameters, we show that significant cooling losses may occur due to inelastic excitations to the hyperfine state and subsequent decays, with implications for the evolution of low-mass halos and the early growth of supermassive black holes. Cooling from excitations to higher $n$ levels of dark hydrogen and subsequent decays is possible at the cluster scale, with a strong dependence on halo mass. Finally, we show that the minimum halo mass is in the range of $10^{3.5}$ to $10^7{M}_{\odot }$ for the viable regions of parameter space, significantly larger than the typical predictions for weakly interacting dark matter models. This pattern of observables in cosmological structure formation is unique to this model, making it possible to rule in or rule out hidden sector hydrogen as a viable dark matter model.

On September 14, 2015 the Advanced LIGO detectors observed their first gravitational wave (GW) transient GW150914. This was followed by a second GW event observed on December 26, 2015. Both events were inferred to have arisen from the merger of black holes in binary systems. Such a system may emit neutrinos if there are magnetic fields and disk debris remaining from the formation of the two black holes. With the surface detector array of the Pierre Auger Observatory we can search for neutrinos with energy $E_{\nu }$ above 100 PeV from pointlike sources across the sky with equatorial declination from about $-65°$ to $+60°$, and, in particular, from a fraction of the 90% confidence-level inferred positions in the sky of GW150914 and GW151226. A targeted search for highly inclined extensive air showers, produced either by interactions of downward-going neutrinos of all flavors in the atmosphere or by the decays of tau leptons originating from tau-neutrino interactions in the Earth’s crust (Earth-skimming neutrinos), yielded no candidates in the Auger data collected within $\pm 500\mathrm{s}$ around or 1 day after the coordinated universal time (UTC) of GW150914 and GW151226, as well as in the same search periods relative to the UTC time of the GW candidate event LVT151012. From the nonobservation we constrain the amount of energy radiated in ultrahigh-energy neutrinos from such remarkable events.

In the context of a $U(1)$ gauge theory nonminimally coupled to scalar-tensor gravity, we find a cosmological attractor solution that represents a de Sitter universe with a homogeneous magnetic field. The solution fully takes into account backreaction of the magnetic field to the geometry and the scalar field. Such a solution is made possible by scaling-type global symmetry and fine-tuning of two parameters of the theory. If the fine-tuning is relaxed then the solution is deformed to an axisymmetric Bianchi type-I universe with constant curvature invariants, a homogeneous magnetic field and a homogeneous electric field. Implications to inflationary magnetogenesis are briefly discussed.

We present results for pion polarizabilities predicted using dispersion relations from our earlier amplitude analysis of world data on two photon production of meson pairs. The helicity-zero polarizabilities are rather stable and insensitive to uncertainties in cross-channel exchanges. The need is first to confirm the recent result on $({\alpha }_1-{\beta }_1)$ for the charged pion by COMPASS at CERN to an accuracy of 10% by measuring the $\gamma \gamma \to {\pi }^{+}{\pi }^{-}$ cross section to an uncertainty of 1%. Then the same polarizability, but for ${\pi }^0$, is fixed to be $({\alpha }_1-{\beta }_1{)}_{{\pi }^0}=(0.9\pm 0.2)\times {10}^{-4}{\mathrm{fm}}^3$. By analyzing the correlation between uncertainties in the meson polarizability and those in $\gamma \gamma$ cross sections, we suggest experiments need to measure these cross sections between $\sqrt{s}\simeq 350$ and 600 MeV. The ${\pi }^0{\pi }^0$ cross section then makes the $({\alpha }_2-{\beta }_2{)}_{{\pi }^0}$ the easiest helicity-two polarizability to determine.