The center of the Milky Way is a host to energetic phenomena across many electromagnetic wave bands and now possibly of high-energy neutrinos. We show that 5 out of 21 IceCube showerlike events, including a PeV event, likely originated from the Galactic Center region. A hard spectrum and flux inferred from these events are inconsistent with atmospheric neutrinos. The flux of these neutrinos is consistent with an extrapolation of the gamma-ray flux measured by Fermi-LAT from the inner Galactic region. This indicates a common hadronic origin of both, powered by supernovae. Three other showerlike events are spatially correlated with the Fermi bubbles, originating from the Galactic Center activity, within the uncertainty of reconstructing their arrival directions. The origin of the other neutrino events, including 7 tracklike events, is still elusive.

The drag force and diffusion coefficients for a $D$ meson are calculated in hot dense matter composed of light mesons and baryons, such as formed in heavy-ion collisions. We use a unitarized approach based on effective models for the interaction of a $D$ meson with hadrons, which are compatible with chiral and heavy quark symmetries. We study the propagation of the $D$ meson in hadron matter in two distinct cases. On the one hand, we analyze the propagation of $D$ mesons in matter at vanishing baryochemical potential ${\mu }_B$, which is relevant for high-energy collisions at the LHC or relativistic heavy ion collider. On the other hand, we show the propagation of $D$ mesons in the hadronic medium following isentropic trajectories, appropriate at Facility for Antiproton and Ion Research and Nuclotron-based Ion Collider Facility heavy-ion experiments. We find a negligible baryon contribution to the transport coefficients at ${\mu }_B=0$. However, at ${\mu }_B>0$ we obtain a large correction to the transport coefficients with the inclusion of nucleons and $\Delta$ baryons. The relaxation time for $D$ mesons is reduced by a factor 2–3 in the latter case, producing a more thermalized $D$-meson spectrum for Facility for Antiproton and Ion Research physics than for the typical LHC energies. We finally present results for the spatial diffusion coefficient of a $D$ meson in hadronic matter and the possible existence of a minimum near the phase transition to the quark-gluon plasma at zero and finite baryochemical potential.

We study the effects of momentum relaxation on observables in a recently proposed holographic model in which the conservation of momentum in the field theory is broken by the presence of a bulk graviton mass. In the hydrodynamic limit, we show that these effects can be incorporated by a simple modification of the energy-momentum conservation equation to account for the dissipation of momentum over a single characteristic time scale. We compute this time scale as a function of the graviton mass terms and identify the previously known “wall of stability” as the point at which this relaxation time scale becomes negative. We also calculate analytically the zero temperature AC conductivity at low frequencies. In the limit of a small graviton mass this reduces to the simple Drude form, and we compute the corrections to this which are important for larger masses. Finally, we undertake a preliminary investigation of the stability of the zero temperature black brane solution of this model, and rule out spatially modulated instabilities of a certain kind.

A fully general-covariant formulation of statistical mechanics is still lacking. We take a step toward this theory by studying the meaning of statistical equilibrium for coupled, parametrized systems. We discuss how to couple parametrized systems. We express the thermalization hypothesis in a general-covariant context. This takes the form of vanishing of information flux. An interesting relation emerges between thermal equilibrium and gauge.

We perform state-of-the-art large-scale shell-model calculations of the structure factors for elastic spin-dependent WIMP scattering off ${}^{129,131}\mathrm{Xe}$, ${}^{127}\mathrm{I}$, ${}^{73}\mathrm{Ge}$, ${}^{19}\mathrm{F}$, ${}^{23}\mathrm{Na}$, ${}^{27}\mathrm{Al}$, and ${}^{29}\mathrm{Si}$. This comprehensive survey covers the nonzero-spin nuclei relevant to direct dark matter detection. We include a pedagogical presentation of the formalism necessary to describe elastic and inelastic WIMP-nucleus scattering. The valence spaces and nuclear interactions employed have been previously used in nuclear structure calculations for these mass regions and yield a good spectroscopic description of these isotopes. We use spin-dependent WIMP-nucleus currents based on chiral effective field theory at the one-body level and including the leading long-range two-body currents due to pion exchange, which are predicted in chiral effective field theory. Results for all structure factors are provided with theoretical error bands due to the nuclear uncertainties of WIMP currents in nuclei.

Recent work in relative locality has shown that the theory allows for a solution of an on-shell causal loop. We show that the theory contains a different type of loop in which locally momenta are conserved, but there is no global momentum conservation. Thus a freely propagating particle can decay into two particles, which later recombine to give a particle with momentum and mass different than the original one.

The dynamics of fluids in which the constituent particles carry non-Abelian charges can be described succinctly in terms of group-valued variables via a generalization of the coadjoint orbit action for particles. This formalism, which is particularly suitable for incorporating anomalies, has previously been used for the chiral magnetic and chiral vorticity effects. Here we consider the similar effect for the isospin which corresponds to an angular asymmetry for neutral pions.

In this paper we derive a hierarchy of integral equations from the 4PI effective action which have the form of Bethe-Salpeter equations. We show that, together with the equation of motion for the self-consistent 4-vertex, these integral equations are closed, and that their expansions give infinite series of connected diagrams which have the correct symmetry.

It is proved that, in order to avoid the ghost mode in bigravity theory, it is sufficient to impose four conditions on the potential of interaction of the two metrics. First, the potential should allow its expression as a function of components of the two metrics’ $3+1$ decomposition. Second, the potential must satisfy the first order linear differential equations which are necessary for the presence of four first class constraints in bigravity. Third, the potential should be a solution of the Monge-Ampère equation, where the lapse and shift are considered as variables. Fourth, the potential must have a nondegenerate Hessian in the shift variables. The proof is based on the explicit derivation of the Hamiltonian constraints, the construction of Dirac brackets on the base of a part of these constraints, and calculation of other constraints’ algebra in these Dirac brackets. As a byproduct, we prove that these conditions are also sufficient in the massive gravity case.

We investigate the possibility of a new massive gravity theory with derivative interactions as an extension of de Rham-Gabadadze-Tolley massive gravity. We find the most general Lagrangian of derivative interactions using a Riemann tensor whose cutoff energy scale is ${\Lambda }_3$, which is consistent with de Rham-Gabadadze-Tolley massive gravity. Surprisingly, this infinite number of derivative interactions can be resummed with the same method in de Rham-Gabadadze-Tolley massive gravity, and remaining interactions contain only two parameters. We show that the equations of motion for scalar and tensor modes in the decoupling limit contain fourth derivatives with respect to spacetime, which implies the appearance of ghosts at ${\Lambda }_3$. We claim that consistent derivative interactions in de Rham-Gabadadze-Tolley massive gravity have a mass scale $M$, which is much smaller than the Planck mass $M_{\mathrm{Pl}}$.

We study the collapse of inhomogeneous dust and null dust (Vaidya radiation) in pure Lovelock gravity in higher dimensions. Since pure Lovelock gravity is kinematic in odd $D=2N+1$ dimensions, the pertinent dimension for the study is even $D=2N+2$, where $N$ is the degree of the Lovelock polynomial. It turns out that pure Lovelock collapse favors a naked singularity against a black hole for the Einstein case in the same dimension, while the strength of the singularity as measured by divergence of the Kretschmann scalar is interestingly the same in the two cases; i.e., the corresponding scalars have the same falloff behavior.

We explore a class of compact charged spheres made of a charged perfect fluid with a polytropic equation of state. The charge density is chosen to be proportional to the energy density. The study is performed by solving the Tolman-Oppenheimer-Volkoff equation, which describes the hydrostatic equilibrium. We show the dependence of the structure of the spheres for several characteristic values of the polytropic exponent and for different values of the charge densities. We also study other physical properties of the charged spheres, such as the total mass, total charge, radius and sound speed and their dependence on the polytropic exponent. We find that for the polytropic exponent $\gamma =4/3$ the Chandrasekhar mass limit coincides with the Oppenheimer-Volkoff mass limit. We test the Oppenheimer-Volkoff limit for such compact objects. We also analyze the Buchdahl limit for these charged polytropic spheres, which happens in the limit of very high polytropic exponents, i.e., for a stiff equation of state. It is found that this limit is extremal and it is a quasiblack hole.

We set up in detail the general formalism to model polytropic general relativistic stars with anisotropic pressure. We shall consider two different possible polytropic equations, all of which yield the same Lane-Emden equation in the Newtonian limit. A heuristic model based on an ansatz to obtain anisotropic matter solutions from known solutions for isotropic matter is adopted to illustrate the effects of the pressure anisotropy on the structure of the star. In this context, the Tolman mass, which is a measure of the active gravitational mass, is invoked to explain some features of the models. Prospective extensions of the proposed approach are pointed out.

The cosmic microwave background (CMB) temperature anisotropies from primordial magnetic fields are studied. In addition to the known passive and compensated modes we discuss an inflationary magnetic mode in the curvature perturbation, present when magnetic fields are generated during inflation. This mode is absent if the generation mechanism is causal, e.g. a phase transition. We compute and discuss the effect of this mode on the observed CMB anisotropy spectrum, in comparison with the passive and compensated ones. We find that it dominates the CMB anisotropy, and consequently leads to stronger constraints on the amplitude $B_{1\mathrm{Mpc}}$ and spectral index $n_B$ of the magnetic field than what is usually found in CMB analyses from the compensated mode. This happens in particular for spectral indexes $n_B>-3$: the inflationary magnetic mode is always scale invariant; therefore through this mode even a magnetic field with a spectrum which is not scale invariant can leave a detectable signal in the CMB at large scales.

We study curved isotropic cosmologies filled with two interacting fluids near their time singularities. We find that a number of these universes asymptote to flat limits in the sense that their asymptotic properties become indistinguishable from those of flat Friedmann-Robertson-Walker models on approach to the singularity along any asymptotic direction. In particular, there are no essential singularities in these models. We discuss connections of this result with possible extensions of the cosmic no hair theorem to the case of two interacting fluids, and also provide links to a quantum cosmological treatment of real and complex Euclidean such solutions.

The increasing precision of cosmological data provides us with an opportunity to test general relativity (GR) on the largest accessible scales. Parameterizing modified gravity models facilitates the systematic testing of the predictions of GR and gives a framework for detecting possible deviations from it. Several different parameterizations have already been suggested, some linked to classifications of theories, and others more empirically motivated. Here we describe a particular new approach which casts modifications to gravity through two free functions of time and scale, which are directly linked to the field equations, but also easy to confront with observational data. We compare our approach with other existing methods of parameterizing modified gravity, specifically the parameterized post-Friedmann approach and the older method using the parameter set $\{\mu ,\gamma \}$. We explain the connection between our parameters and the physics that is most important for generating cosmic microwave background anisotropies. Some qualitative features of this new parameterization, and therefore modifications to the gravitational equations of motion, are illustrated in a toy model, where the two functions are simply assumed to be constant parameters.

We investigate the gravitational constraints imposed on dark matter halos in the context of finite temperature scalar field dark matter. We find constraints to produce multiple images by dark matter, and we show that there are differences with respect to the full Bose-Einstein condensate halo when the temperature of the scalar field in dark matter halos is taken into account. The nonzero temperature allows the scalar field to be in excited states, and, recently, their existence has proven to be necessary to fit rotation curves of dark matter dominated galaxies of all sizes, and it also explained the nonuniversality of the halo density profiles. Therefore, we expect that combining observations of rotation curves and strong lensing systems can give us a clue to the nature of dark matter. Finally, we propose a method to identify the excited state of a halo in a strong lens system, knowing that various halo excited states can provide information of the scalar field dark matter halo evolution which can be tested by using numerical simulations.

The Tevatron, where the top quark was discovered, and the currently functional Large Hadron Collider (LHC), with copiously produced top pairs, enable a detailed study of top-quark properties. In particular, they can be used to test the couplings of the top quark to gauge bosons. Several extensions of the standard model (SM) can give rise to anomalous couplings of the top quark to gauge bosons, in particular, the gluons. In this work we examine how top-quark polarization, which is predicted to be negligibly small in the SM, can be used to measure chromomagnetic and chromoelectric couplings of the top quark to gluons. We place special emphasis on the use of angular distributions and asymmetries of charged leptons arising from top decay as measures of top polarization and hence of these anomalous couplings. Sensitivities that may be reached at the Tevatron and the LHC are obtained.

We compute the dependence of the Higgs to two-photon decay rate ${\Gamma }_{h\to \gamma \gamma }$ on the top quark gyromagnetic factor $g_t$ in the heavy top limit and evaluate the expected change for one-loop SM correction to $g_t$. Our results are general and allow consideration of further modifications of $g_t$, and we predict the resultant ${\Gamma }_{h\to \gamma \gamma }$.