Soft interactions with high-energy jets are explored in radial coordinates which exploit the approximately conformal behavior of perturbative gauge theories. In these coordinates, the jets, approximated by Wilson lines, become static charges in Euclidean AdS. The anomalous dimension of the corresponding Wilson line operator is then determined by the potential energy of the charges. To study these Wilson lines we introduce a “conformal gauge” which does not have kinetic mixing between radial and angular directions, and show that a number of properties of Wilson lines are reproduced through relatively simple calculations. For example, certain nonplanar graphs involving multiple Wilson lines automatically vanish. We also discuss the linear growth of the charges’ imaginary potential energy with separation, and a relationship between Wilson line diagrams and Witten diagrams.

In this paper, we employ the equation of state (EOS) of the quasiparticle model proposed in A. M. Zhao et al., Mod. Phys. Lett. A 25, 47 (2010)] which incorporates the effect of vacuum negative pressure to study the properties of quark stars. In our model the EOS has the correct behavior required by QCD in the small and large $\mu$ limit. We employ this EOS to calculate the mass-radii relation and mass-energy density relation of quark stars. Our results are found to be consistent with the most recent astronomical observations.

We develop a systematic field theoretic description of roughness corrections to the Casimir free energy of a massless scalar field in the presence of parallel plates with mean separation $a$. Roughness is modeled by specifying a generating functional for correlation functions of the height profile. The two-point correlation function being characterized by its variance, ${\sigma }^2$, and correlation length, $\ell$. We obtain the partition function of a massless scalar quantum field interacting with the height profile of the surface via a $\delta$-function potential. The partition function is given by a holographic reduction of this model to three coupled scalar fields on a two-dimensional plane. The original three-dimensional space with a flat parallel plate at a distance $a$ from the rough plate is encoded in the nonlocal propagators of the surface fields on its boundary. Feynman rules for this equivalent $2+1$-dimensional model are derived and its counterterms constructed. The two-loop contribution to the free energy of this model gives the leading roughness correction. The effective separation, $a_{\mathrm{eff}}$, to a rough plate is measured to a plane that is displaced a distance $\rho \propto {\sigma }^2/\ell$ from the mean of its profile. This definition of the separation eliminates corrections to the free energy of order $1/a^4$ and results in unitary scattering matrices. We obtain an effective low-energy model in the limit $\ell \ll a$. It determines the scattering matrix and equivalent planar scattering surface of a very rough plate in terms of the single length scale $\rho$. The Casimir force on a rough plate is found to always weaken with decreasing correlation length $\ell$. The two-loop approximation to the free energy interpolates between the free energy of the effective low-energy model and that of the proximity force approximation – the force on a very rough plate with $\sigma \gtrsim 0.5\ell$ being weaker than on a planar Dirichlet surface at any separation.

We investigate the validity of the hyperhoop conjecture, which claims to determine a necessary and sufficient condition for the formation of black hole horizons in higher-dimensional space-times. Here we consider momentarily static, conformally flat initial data sets, each describing a gravitational field of uniform massive $k$-sphere sources, for $k=1,2$, on the five-dimensional Cauchy surface. The numerical result shows the validity of the hyperhoop conjecture for a wide range of model parameters. We also confirm for the first time the existence of an apparent horizon homeomorphism to $S^2\times S^2$ or $S^1\times S^3$, which is a higher-dimensional generalization of the black ring.

The characteristic formalism of numerical relativity is based on a system of coordinates aligned with outgoing null cones. While these coordinates were designed for studying gravitational waves, they can also be easily adapted to model cosmological past null cones (PNCs). Similar to observational coordinates in the observational approach to cosmology, this then provides a model that only makes use of information causally connected to an observer. However, the diameter distance, which is used as a radial coordinate, limits the model’s cosmological application to the region prior to the PNC refocusing. This is because after refocusing, the diameter distance ceases to be a unique measure of distance. This paper addresses the problem by introducing a metric based on the Bondi-Sachs metric where the radial coordinate is replaced by an affine parameter. A model is derived from this metric and it is then shown how an existing numerical scheme can be adapted for simulation of cosmological PNC behavior. Numerical calculations on this model are found to have the same stability and convergence properties as the standard characteristic formalism.

General relativistic simulations of black hole-neutron star mergers have currently been limited to low-mass black holes ($M_{\mathrm{BH}}\le 7M_{\odot }$), even though population synthesis models indicate that a majority of mergers might involve more massive black holes ($M_{\mathrm{BH}}\ge 10M_{\odot }$). We present the first general relativistic simulations of black hole-neutron star mergers with $M_{\mathrm{BH}}\sim 10M_{\odot }$. For massive black holes, the tidal forces acting on the neutron star are usually too weak to disrupt the star before it reaches the innermost stable circular orbit of the black hole. Varying the spin of the black hole in the range $a_{\mathrm{BH}}/M_{\mathrm{BH}}=0.5–0.9$, we find that mergers result in the disruption of the star and the formation of a massive accretion disk only for large spins $a_{\mathrm{BH}}/M_{\mathrm{BH}}\ge 0.7–0.9$. From these results, we obtain updated constraints on the ability of black hole-neutron star mergers to be the progenitors of short gamma-ray bursts as a function of the mass and spin of the black hole. We also discuss the dependence of the gravitational wave signal on the black hole parameters, and provide waveforms and spectra from simulations beginning 7–8 orbits before the merger.

For a general class of analytic functions $f(R,R_{\alpha \beta }{R}^{\alpha \beta },R_{\alpha \beta \gamma \delta }{R}^{\alpha \beta \gamma \delta })$ we discuss the gravitational lensing in the Newtonian limit of theory. From the properties of the Gauss-Bonnet invariant it is enough to consider only one curvature invariant between the Ricci tensor and the Riemann tensor. Then, we analyze the dynamics of a photon embedded in a gravitational field of a generic $f(R,R_{\alpha \beta }{R}^{\alpha \beta })$ gravity. The metric is time independent and spherically symmetric. The metric potentials are Schwarzschild-like, but there are two additional Yukawa terms linked to derivatives of $f$ with respect to two curvature invariants. Considering first the case of a pointlike lens, and after the one of a generic matter distribution of the lens, we study the deflection angle and the angular position of images. Though the additional Yukawa terms in the gravitational potential modifies dynamics with respect to general relativity, the geodesic trajectory of the photon is unaffected by the modification if we consider only $f(R)$ gravity. We find different results (deflection angle smaller than the angle of general relativity) only due to the introduction of a generic function of the Ricci tensor square. Finally, we can affirm that the lensing phenomena for all $f(R)$ gravities are equal to the ones known for general relativity. We conclude the paper by showing and comparing the deflection angle and position of images for $f(R,R_{\alpha \beta }{R}^{\alpha \beta })$ gravity with respect to the gravitational lensing of general relativity.

Behavior of Dirac fermions in the background of a charged black string penetrated by an Abelian Higgs vortex is elaborated. One finds evidence that the system under consideration can support fermion fields acting like a superconducting cosmic string in the sense that a nontrivial Dirac fermion field can be carried by the system in question. Nonextremal and extremal black string vortex systems were considered. The influence of electric and Higgs charge, the winding number, and the fermion mass on the fermion localization near the black string event horizon were studied. It turned out that the extreme charged black string expelled fermion fields more violently comparing to the nonextremal one.

We construct a domain wall solution in $F(R)$ gravity. We reconstruct a static domain wall solution in a scalar field theory. We also reconstruct an explicit $F(R)$ gravity model in which a static domain wall solution can be realized. Moreover, we show that there could exist an effective (gravitational) domain wall in the framework of $F(R)$ gravity. In addition, it is demonstrated that a logarithmic nonminimal gravitational coupling of the electromagnetic theory in $F(R)$ gravity may produce time variation of the fine structure constant which may increase with decrease of the curvature, and that this model would be ruled out by the constraints on the time variation of the fine structure constant from quasar absorption lines. We also present cosmological consequences of the coupling of the electromagnetic field to a scalar field as well as the scalar curvature and discuss the relation between variation of the fine structure constant and the breaking of the conformal invariance of the electromagnetic field.

A characteristic feature of loop quantization of the isotropic and Bianchi-I spacetimes is the existence of universal bounds on the energy density and the expansion and shear scalars, independent of the matter content. We investigate the properties of these physical quantities in Bianchi-II and Bianchi-IX spacetimes, which have been recently loop quantized using the connection operator approach. Using the effective Hamiltonian approach, we show that for Bianchi-II spacetime the energy density and the expansion and shear scalars turn out to be bounded, albeit not by universal values. In Bianchi-IX spacetime, when the approach to the classical singularity is isotropic, the above physical quantities are bounded. In addition, for all other cases, where the approach to singularities is not isotropic and effective dynamics can be trusted, these quantities turn out to be finite. These results stand in sharp distinction to general relativity, where the above physical quantities are generically unbounded, leading to the breakdown of geodesic equations. In contrast to the isotropic and Bianchi-I models, we find the role of energy conditions for the Bianchi-II model and the inverse triad modifications for Bianchi-IX to be significant to obtain the above bounds. These results bring out subtle physical distinctions between (i) the quantization using holonomies over closed loops performed for isotropic and Bianchi-I models and (ii) the connection operator approach. We find that qualitative differences in physics exist for these quantization methods even for the isotropic models in the presence of spatial curvature. We highlight these important differences in the behavior of the expansion scalar in the holonomy based quantization and connection operator approach for isotropic spatially closed and open models.

We perform the Hamiltonian analysis of $1+1$-dimensional nonlinear massive gravity studied in [C. de Rham, G. Gabadadze, and A. Tolley, arXiv:1107.3820]. We find the constraint structure of the given theory and perform the counting of the physical degrees of freedom.

The next generation of weak lensing surveys will trace the evolution of matter perturbations and gravitational potentials from the matter dominated epoch until today. Along with constraining the dynamics of dark energy, they will probe the relations between matter overdensities, local curvature, and the Newtonian potential. We work with two functions of time and scale to account for any modifications of these relations in the linear regime from those in the $\Lambda \mathrm{CDM}$ model. We perform a principal component analysis (PCA) to find the eigenmodes and eigenvalues of these functions for surveys like the Dark Energy Survey and Large Synoptic Survey Telescope. This paper builds on and significantly extends the PCA analysis of Zhao et al. [Phys. Rev. Lett. 103, 241301 (2009)] in several ways. In particular, we consider the impact of some of the systematic effects expected in weak lensing surveys. We also present the PCA in terms of other choices of the two functions needed to parametrize modified growth on linear scales, and discuss their merits. We analyze the degeneracy between the modified growth functions and other cosmological parameters, paying special attention to the effective equation of state $w(z)$. Finally, we demonstrate the utility of the PCA as an efficient data compression stage which enables one to easily derive constraints on parameters of specific models without recalculating Fisher matrices from scratch.

Recently, the PAMELA collaboration published the cosmic nuclei and electron spectra with high precision, together with the cosmic antiproton data updated, and the Fermi-LAT collaboration also updated the measurement of the total $e^{+}{e}^{-}$ spectrum to lower energies. In this paper we develop a Markov Chain Monte Carlo (MCMC) package CosRayMC, based on the Galactic Propagation (GALPROP) cosmic ray propagation model to study the implications of these new data. It is found that if only the background electrons and secondary positrons are considered, the fit is very bad with ${\chi }_{\mathrm{red}}^2\approx 3.39$. Taking into account the extra $e^{+}{e}^{-}$ sources of pulsars or dark matter annihilation we can give much better fit to these data, with the minimum ${\chi }_{\mathrm{red}}^2\approx 1.04$. This means the extra sources are necessary with a very high significance in order to fit the data. However, the data show little difference between pulsar and dark matter scenarios. Both the background and extra source parameters are well constrained with this MCMC method. The antiproton data can further constrain the branching ratio of dark matter annihilation into quarks to be $B_q<0.5\%$ at $2\sigma$ confidence level. The possible systematical uncertainties of the present study are discussed.

Averaging in general relativity is a complicated operation, due to the general covariance of the theory and the nonlinearity of Einstein’s equations. The latter of these ensures that smoothing spacetime over cosmological scales does not yield the same result as solving Einstein’s equations with a smooth matter distribution, and that the smooth models we fit to observations need not be simply related to the actual geometry of spacetime. One specific consequence of this is a decoupling of the geometrical spatial curvature term in the metric from the dynamical spatial curvature in the Friedmann equation. Here we investigate the consequences of this decoupling by fitting to a combination of Hubble Space Telescope (HST), CMB, type Ia supernovae (SNIa), and baryon acoustic oscillation (BAO) data sets. We find that only the geometrical spatial curvature is tightly constrained and that our ability to constrain dark energy dynamics will be severely impaired until we gain a thorough understanding of the averaging problem in cosmology.

Branons are new degrees of freedom that appear in flexible brane-world models corresponding to brane fluctuations. These new fields can behave as standard weakly interacting massive particles (WIMPs) with a significant associated thermal relic density. We analyze the present constraints from their spontaneous annihilations into photons for Energetic Gamma-Ray Experiment Telescope (EGRET), Fermi-Large Area Telescope (LAT), and Major Atmospheric Gamma-Ray Imaging Cherenkov (MAGIC) telescopes, and the prospects for detection in future Cherenkov telescopes. In particular, we focus on possible signals coming from the Galactic center and different dwarf spheroidals, such as Draco, Sagittarius, Canis Major and SEGUE 1. We conclude that for those targets, present observations are below the sensitivity limits for branon detection by assuming standard dark matter distributions and no additional boost factors. However, future experiments such as the Cherenkov Telescope Array (CTA) could be able to detect gamma-ray photons coming from the annihilation of branons with masses higher than 150 GeV.

Gaussianity of temperature fluctuations in the Cosmic Microwave Background (CMB) implies that the statistical properties of the temperature field can be completely characterized by its two-point correlation function. The two-point correlation function can be expanded in full generality in the Bipolar Spherical Harmonic (BipoSH) basis. Looking for significant deviations from zero for BipoSH coefficients derived from observed CMB maps forms the basis of the strategy used to detect isotropy violation. In order to quantify “significant deviation” we need to understand the distributions of these coefficients. We analytically evaluate the moments and the distribution of the coefficients of expansion ($A_{l_1{l}_2}^{LM}$), using the characteristic function approach. We show that for BipoSH coefficients with $M=0$ an analytical form for the moments up to any arbitrary order can be derived. For the remaining BipoSH coefficients with $M\ne 0$, the moments derived using the characteristic function approach need to be supplemented with a correction term. The correction term is found to be important particularly at low multipoles. We provide a general prescription for calculating these corrections, however we restrict the explicit calculations only up to kurtosis. We confirm our results with measurements of BipoSH coefficients on numerically simulated statistically isotropic CMB maps.

As is known, more than 90% of the energy content in the Universe is made of unknown dark component. Usually this dark fluid is separated into two parts: dark matter and dark energy. However, it may be a mixture of these two energy components, or just one exotic unknown fluid. This property is dubbed as dark degeneracy. With this motivation, in this paper, a unified dark fluid having constant adiabatic sound speed $c_s^2=\alpha$, which is in the range $[0,1]$, is studied. At first, via the energy conservation equation, its energy density, ${\rho }_d/{\rho }_{d0}=(1-B_s)+B_s{a}^{-3(1+\alpha )}$ where $B_s$ is related to integration constant from energy conservation equation as another model parameter, is presented. Then by using the Markov Chain Monte Carlo method with currently available cosmic observational data sets which include type Ia supernova Union 2, baryon acoustic oscillation, and WMAP 7-year data of cosmic background radiation, we show that small values of $\alpha$ are favored in this unified dark fluid model. Furthermore, we show that smaller values of $\alpha <{10}^{-5}$ are required to match matter (baryon) power spectrum from SDSS DR7.

Current gravitational wave searches for compact binaries coalescence are done using a bank of templates (matched filters) on each running detector. Given a network of interferometers, we propose to use a denoising strategy based on an independent component analysis which considers two interferometers at a time and then to use a standard matched filter on the processed data. We show that this method allows to lower the level of noise and increases the signal-to-nose ratio at the output of the matched filter.

We analyze the stability of the vacuum and the electroweak phase transition in the NMSSM close to the Peccei-Quinn symmetry limit. This limit contains light dark matter (DM) particles with a mass significantly smaller than the weak scale and also light $CP$-even and $CP$-odd Higgs bosons. Such light particles lead to a consistent relic density and facilitate a large spin-independent direct DM detection cross section, that may accommodate the recently reported signatures at the DAMA and CoGeNT experiments. Studying the one-loop effective potential at finite temperature, we show that when the lightest $CP$-even Higgs mass is of the order of a few GeV, the electroweak phase transition tends to become first order and strong. The inverse relationship between the direct-detection cross section and the lightest $CP$-even Higgs mass implies that a cross section of the order of ${10}^{-41}{\mathrm{cm}}^2$ is correlated with a strong first-order phase transition.

The experimental data on the processes $\pi \pi \to \pi \pi$, $K\overline{K}$, $\eta \eta$, $\eta {\eta }^{\prime }$ in the $I^G{J}^{PC}=0^{+}{0}^{++}$ channel have been jointly analyzed to study the status and nature of the $f_0$. The method of analysis is based on analyticity and unitarity and uses an uniformization procedure. Some spectroscopic implications from results of the analysis are discussed.