We present the baseline multimessenger analysis method for the joint observations of gravitational waves (GW) and high-energy neutrinos (HEN), together with a detailed analysis of the expected science reach of the joint search. The analysis method combines data from GW and HEN detectors, and uses the blue-luminosity-weighted distribution of galaxies. We derive expected $\mathrm{GW}+\mathrm{HEN}$ source rate upper limits for a wide range of source parameters covering several emission models. Using published sensitivities of externally triggered searches, we derive joint upper limit estimates both for the ongoing analysis with the initial LIGO-Virgo GW detectors with the partial IceCube detector (22 strings) HEN detector and for projected results to advanced LIGO-Virgo detectors with the completed IceCube (86 strings). We discuss the constraints these upper limits impose on some existing $\mathrm{GW}+\mathrm{HEN}$ emission models.

The microscopic spectral density of the Wilson Dirac operator for two-flavor lattice QCD is analyzed. The computation includes the leading order $a^2$ corrections of the chiral Lagrangian in the microscopic limit. The result is used to demonstrate how the Sharpe-Singleton first order scenario is realized in terms of the eigenvalues of the Wilson Dirac operator. We show that the Sharpe-Singleton scenario only takes place in the theory with dynamical fermions whereas the Aoki phase can be realized in the quenched as well as the unquenched theory. Moreover, we give constraints imposed by ${\gamma }_5$ Hermiticity on the additional low energy constants of Wilson chiral perturbation theory.

We have developed a phenomenological approach which describes very well the ${\pi }^0$, $\eta$ and ${\eta }^{\prime }$ meson production in the two-photon interactions. The simultaneous description of the ${\pi }^0$, $\eta$ and ${\eta }^{\prime }$ meson two-photon form factors is consistent with data in the spacelike region, with the exception of the ${\pi }^0$ BABAR data. The obtained form factors are implemented in the event generator EKHARA and the simulated cross sections are presented. Uncertainties in the measured form factors coming from the model dependence in Monte Carlo simulations are studied. The model predictions for the form factor slopes at the origin are given and the high-$Q^2$ limit is also discussed.

During the 2010 rainy season in Yangbajing (4300 m above sea level) in Tibet, China, a long-duration count enhancement associated with thunderclouds was detected by a solar-neutron telescope and neutron monitors installed at the Yangbajing Comic Ray Observatory. The event, lasting for $\sim 40\min$, was observed on July 22, 2010. The solar-neutron telescope detected significant $\gamma$-ray signals with energies $>40\mathrm{MeV}$ in the event. Such a prolonged high-energy event has never been observed in association with thunderclouds, clearly suggesting that electron acceleration lasts for 40 min in thunderclouds. In addition, Monte Carlo simulations showed that $>10\mathrm{MeV}$ $\gamma$ rays largely contribute to the neutron monitor signals, while $>1\mathrm{keV}$ neutrons produced via a photonuclear reaction contribute relatively less to the signals. This result suggests that enhancements of neutron monitors during thunderstorms are not necessarily clear evidence for neutron production, as previously thought.

Our previous study of a system of bodies assumed to move along almost-circular orbits around a central mass, approximately described by Hill’s equations, is extended to exotic (alias noncommutative) particles. For a certain critical value of the angular velocity, the only allowed motions follow the Hall law. Translations and generalized boosts span two independent Heisenberg algebras with different central parameters. In the critical case, the symmetry reduces to a single Heisenberg algebra.

In this paper we analyze super-Chern-Simons theory in $\mathcal{N}=1$ superspace formalism, in the presence of a boundary. We modify the Lagrangian for the Chern-Simons theory in such a way that it is supersymmetric even in the presence of a boundary. Also, even though the Chern-Simons theory is not gauge invariant in the presence of a boundary, if it is suitably coupled to a gauged Wess-Zumino-Witten model, then the resultant theory can be made gauge invariant. Thus, by suitably adding extra boundary degrees of freedom, the gauge and supersymmetry variations of the boundary theory exactly cancel the boundary terms generated by the variations of the bulk Chern-Simons theory. We also discuss how this can be applied to the Aharony-Bergman-Jafferis-Maldacena model in $\mathcal{N}=1$ superspace, and we then describe the Becchi-Rouet-Stora-Tyutin (BRST) and anti-BRST symmetries of the resultant gauge invariant supersymmetric theory.

We construct analytical and numerical vortex solutions for an extended Skyrme-Faddeev model in a $(3+1)$ dimensional Minkowski space-time. The extension is obtained by adding to the Lagrangian a quartic term, which is the square of the kinetic term, and a potential which breaks the $SO(3)$ symmetry down to $SO(2)$. The construction makes use of an ansatz, invariant under the joint action of the internal $SO(2)$ and three commuting $U(1)$ subgroups of the Poincaré group, and which reduces the equations of motion to an ordinary differential equation for a profile function depending on the distance to the $x^3$ axis. The vortices have finite energy per unit length, and have waves propagating along them with the speed of light. The analytical vortices are obtained for a special choice of potentials, and the numerical ones are constructed using the successive over relaxation method for more general potentials. The spectrum of solutions is analyzed in detail, especially its dependence upon special combinations of coupling constants.

We revisit the problem of dipole-dipole scattering via exchanges of soft Pomerons in the context of holographic QCD. We show that a single closed string exchange contribution to the eikonalized dipole-dipole scattering amplitude yields a Regge behavior of the elastic amplitude; the corresponding slope and intercept are different from previous results obtained by a variational analysis of semiclassical surfaces. We provide a physical interpretation of the semiclassical worldsheets driving the Regge behavior for $(-t)>0$ in terms of worldsheet instantons. The latter describe the Schwinger mechanism for string pair creation by an electric field, where the longitudinal electric field $E_L={\sigma }_T\tanh (\chi /2)$ at the origin of this nonperturbative mechanism is induced by the relative rapidity $\chi$ of the scattering dipoles. Our analysis naturally explains the diffusion in the impact parameter space encoded in the Pomeron exchange; in our picture, it is due to the Unruh temperature of accelerated strings under the electric field. We also argue for the existence of a “micro-fireball” in the middle of the transverse space due to the soft Pomeron exchange, which may be at the origin of the thermal character of multiparticle production in ep/pp collisions. After summing over uncorrelated multi-Pomeron exchanges, we find that the total dipole-dipole cross section obeys the Froissart unitarity bound.

Employing a thermodynamic interpretation of gravity based on the holographic principle and assuming underlying particle statistics, fermionic or bosonic, for the excitations of the holographic screen leads to modified Newtonian dynamics (MOND). A connection between the acceleration scale $a_0$ appearing in MOND and the Fermi energy of the holographic fermionic degrees of freedom is obtained. In this formulation the physics of MOND results from the quantum-classical crossover in the fermionic specific heat. However, due to the dimensionality of the screen, the formalism is general and applies to two-dimensional bosonic excitations as well. It is shown that replacing the assumption of the equipartition of energy on the holographic screen by a standard quantum-statistical-mechanics description wherein some of the degrees of freedom are frozen out at low temperatures is the physical basis for the MOND interpolating function $\tilde{\mu }$. The interpolating function $\tilde{\mu }$ is calculated within the statistical mechanical formalism and compared to the leading phenomenological interpolating functions, most commonly used. Based on the statistical mechanical view of MOND, its cosmological implications are reinterpreted: the connection between $a_0$ and the Hubble constant is described as a quantum uncertainty relation; and the relationship between $a_0$ and the cosmological constant is better understood physically.

To confront relativity theory with observation, it is necessary to split spacetime into its temporal and spatial components. The ($1+3$) timelike threading approach involves restrictions on the gravitational potentials $(g_{\mu \nu })$, while the ($3+1$) spacelike slicing approach involves restrictions on $(g^{\mu \nu })$. These latter coordinate conditions protect chronology within any such coordinate patch. While the threading coordinate conditions can be naturally integrated into the structure of Lorentzian geometry and constitute the standard coordinate conditions in general relativity, this circumstance does not extend to the slicing coordinate conditions. We explore the influence of chronology violation on wave motion. In particular, we consider the propagation of radiation parallel to the rotation axis of stationary Gödel-type universes characterized by parameters $\eta >0$ and $\lambda >0$ such that for $\eta <1$ ($\eta >1$) chronology is protected (violated). We show that in the WKB approximation such waves can freely propagate only when chronology is protected.

There are many factors that contribute to the breaking of the spherical symmetry of a neutron star. Most notable are rotation, magnetic fields, and/or accretion of matter from companion stars. All these phenomena influence the macroscopic structures of neutron stars, but also impact their microscopic compositions. The purpose of this paper is to investigate the cooling of rotationally deformed, two-dimensional (2D) neutron stars in the framework of general relativity theory, with the ultimate goal of better understanding the impact of 2D effects on the thermal evolution of such objects. The equations that govern the thermal evolution of rotating neutron stars are presented in this paper. The cooling of neutron stars with different frequencies is computed self-consistently by combining a fully general relativistic 2D rotation code with a general relativistic 2D cooling code. We show that rotation can significantly influence the thermal evolution of rotating neutron stars. Among the major new aspects are the appearances of hot spots on the poles, and an increase of the thermal coupling times between the core and the crust of rotating neutron stars. We show that this increase is independent of the microscopic properties of the stellar core, but depends only on the frequency of the star.

We present a class of generally covariant nonlocal gravity models which have a flat-space general relativistic limit and also possess a stable de Sitter or anti-de Sitter (AdS) background with an arbitrary value of its cosmological constant. The nonlocal action of the theory is formulated in the Euclidean signature spacetime and is understood as an approximation to the quantum effective action (generating functional of one-particle irreducible diagrams) originating from fundamental quantum gravity theory. Using the known relation between the Schwinger-Keldysh technique for quantum expectation values and the Euclidean quantum field theory we derive from this action the causal effective equations of motion for mean value of the metric field in the physical Lorentzian-signature spacetime. Thus we show that the (A)dS background of the theory carries as free propagating modes massless gravitons having two polarizations identical to those of the Einstein theory with a cosmological term. The on-shell action of the theory is vanishing both for the flat-space and (A)dS backgrounds which play the role of stable vacua underlying, respectively, the ultraviolet and infrared phases of the theory. We also obtain linearized gravitational potentials of compact matter sources and show that in the infrared (A)dS phase their effective gravitational coupling $G_{\mathrm{eff}}$ can be essentially different from the Newton gravitational constant $G_N$ of the short-distance general relativistic phase. When $G_{\mathrm{eff}}\gg G_N$ the (A)dS phase can be regarded as a strongly coupled infrared modification of Einstein theory not only describing the dark energy mechanism of cosmic acceleration but also simulating the dark matter phenomenon by enhanced gravitational attraction at long distances.

We propose a lattice counterpart of diffeomorphism symmetry in the continuum. A functional integral for quantum gravity is regularized on a discrete set of space-time points, with fermionic or bosonic lattice fields. When the space-time points are positioned as discrete points of a continuous manifold, the lattice action can be reformulated in terms of average fields within local cells and lattice derivatives. Lattice diffeomorphism invariance is realized if the action is independent of the positioning of the space-time points. Regular as well as rather irregular lattices are then described by the same action. Lattice diffeomorphism invariance implies that the continuum limit and the quantum effective action are invariant under general coordinate transformations—the basic ingredient for general relativity. In our approach the lattice diffeomorphism invariant actions are formulated without introducing a metric or other geometrical objects as fundamental degrees of freedom. The metric rather arises as the expectation value of a suitable collective field. As examples, we present lattice diffeomorphism invariant actions for a bosonic nonlinear sigma model and lattice spinor gravity.

We show that there is no useful, universal definition of a running gravitational constant, $G(E)$, in the perturbative regime below the Planck scale. By consideration of the loop corrections to several physical processes, we show that the quantum corrections vary greatly, in both magnitude and sign, and do not exhibit the required properties of a running coupling constant. We comment on the potential challenges of these results for the asymptotic safety program.

We investigate the observational consequences of the quintessence field rolling to and oscillating near a minimum in its potential, if it happens close to the present epoch ($z\lesssim 0.2$). We show that in a class of models, the oscillations lead to a rapid growth of the field fluctuations and the gravitational potential on subhorizon scales. The growth in the gravitational potential occurs on time scales $\ll H^{-1}$. This effect is present even when the quintessence parameters are chosen to reproduce an expansion history consistent with observations. For linearized fluctuations, we find that although the gravitational potential power spectrum is enhanced in a scale-dependent manner, the shape of the dark matter/galaxy power spectrum is not significantly affected. We find that the best constraints on such a transition in the quintessence field is provided via the integrated Sachs-Wolfe effect in the CMB-temperature power spectrum. Going beyond the linearized regime, the quintessence field can fragment into large, localized, long-lived excitations (oscillons) with sizes comparable to galaxy clusters; this fragmentation could provide additional observational constraints. Two quoted signatures of modified gravity are a scale-dependent growth of the gravitational potential and a difference between the matter power spectrum inferred from measurements of lensing and galaxy clustering. Here, both effects are achieved by a minimally coupled scalar field in general relativity with a canonical kinetic term. In other words we show that, with some tuning of parameters, scale-dependent growth does not necessarily imply a violation of General Relativity.

We present a new test of gravitational interactions at the $r\simeq (0.2–20)\mathrm{Mpc}$ scale, around the virial radius of dark matter halos measured through cluster-galaxy lensing of maxBCG clusters from the Sloan Digital Sky Survey (SDSS). We employ predictions from self-consistent simulations of $f(R)$ gravity to find an upper bound on the background field amplitude of $|f_{R0}|<3.5\times {10}^{-3}$ at the 1D-marginalized 95% confidence level. As a model-independent assessment of the constraining power of cluster profiles measured through weak gravitational lensing, we also constrain the amplitude $F_0$ of a phenomenological modification based on the profile enhancement induced by $f(R)$ gravity when not including effects from the increased cluster abundance in $f(R)$. In both scenarios, dark-matter-only simulations of the concordance model corresponding to $|f_{R0}|=0$ and $F_0=0$ are consistent with the lensing measurements, i.e., at the 68% and 95% confidence level, respectively.

It has been suggested that new massive gravity with higher order terms in the curvature may be renormalizable and thus a candidate for renormalizable quantum gravity. We show that three-dimensional gravity that contains quadratic scalar curvature and a Ricci tensor is renormalizable, but those theories with a special relation between their coefficients, including new massive gravity, are not.

We present a simplified version of the atomic dark matter scenario, in which charged dark constituents are bound into atoms analogous to hydrogen by a massless hidden sector U(1) gauge interaction. Previous studies have assumed that interactions between the dark sector and the standard model are mediated by a second, massive $Z^{\prime }$ gauge boson, but here we consider the case where only a massless ${\gamma }^{\prime }$ kinetically mixes with the standard model hypercharge and thereby mediates direct detection. This is, therefore, the simplest atomic dark matter model that has direct interactions with the standard model, arising from the small electric charge for the dark constituents induced by the kinetic mixing. We map out the parameter space that is consistent with cosmological constraints and direct searches, assuming that some unspecified mechanism creates the asymmetry that gives the right abundance, since the dark matter cannot be a thermal relic in this scenario. In the special case where the dark electron and proton are degenerate in mass, inelastic hyperfine transitions can explain the CoGeNT excess events. In the more general case, elastic transitions dominate and can be close to current direct-detection limits over a wide range of masses.

We consider a globally neutral Lorentzian plasma as a possible remnant of a preinflationary stage of expansion and pose the problem of the suitable initial conditions for the evolution of the large-scale electromagnetic inhomogeneities. During the protoinflationary regime, the Weyl invariance of the Ohmic current guarantees that the comoving conductivity is approximately constant. The subsequent breaking of Weyl invariance by the masses of the charge carriers drives the conductivity to zero. The newly derived conducting initial conditions for the amplification of large-scale magnetic fields are contrasted with the conventional vacuum initial conditions. It is shown, in a specific class of examples, that when the number of inflationary e-folds is close to minimal, the effects of the conducting initial conditions cannot be neglected.