118544491
Proof of universality of electrical conductivity at finite chemical potential
It was proposed in [1] that, for certain gauge theories with gravity duals, electrical conductivity at finite chemical potential is universal. Here we provide a general proof that, when matter stress tensor satisfies a compact constraint, electrical conductivity is universal. We further elaborate our result with several conformal as well as non-conformal gauge theories. We also discuss how boundary conductivity and universal conductivity of stretched horizon are related.
118709858
Viscosity to entropy ratio at extremality
Assuming gauge theory realization at the boundary, we show that the viscosity to entropy ratio is 1/(4π) where the bulk is represented by a large class of extremal black holes in anti-deSitter space. In particular, this class includes multiple R-charged black holes in various dimensions.
13926216
Asymptotic Quasinormal Modes of d-Dimensional Schwarzschild Black Hole with Gauss-Bonnet Correction
We obtain an analytic expression for the highly damped asymptotic quasinormal mode frequencies of the (d ≥ 5)-dimensional Schwarzschild black hole modified by the Gauss–Bonnet term, which appears in string derived models of gravity. The analytic expression is obtained under the string inspired assumption that there exists a minimum length scale in the system and in the limit when the coupling in front of the Gauss–Bonnet term in the action is small. Although there are several similarities of this geometry with that of the Schwarzschild black hole, the asymptotic quasinormal mode frequencies are quite different. In particular, the real part of the asymptotic quasinormal frequencies for this class of single horizon black holes is not proportional to log(3).
115177789
Scalar field dynamics in warped AdS3 black hole background
Abstract We study the normal modes of a scalar field in the background of a warped AdS 3 black hole which arises in topologically massive gravity. We discuss the normal mode spectrum using the brick wall boundary condition. In addition, we investigate the possibility of a more general boundary condition for the scalar field.
118514124
Cosmology of Hořava–Lifshitz f(R) gravity
Abstract We discuss the cosmology of recently proposed Hořava–Lifshitz f ( R ) gravity. In particular, we derive the modified Hubble equation that reduces to the standard HL gravity case in appropriate limit. We show how the bounce solutions in this theory are modified due to nonlinear effect of f ( R ) gravity. We also show that in principle, the Universe in this set-up can show cyclic behavior.
42578428
Floating and sinking: the imprint of massive scalars around rotating black holes.
We study the coupling of massive scalar fields to matter in orbit around rotating black holes. It is generally expected that orbiting bodies will lose energy in gravitational waves, slowly inspiraling into the black hole. Instead, we show that the coupling of the field to matter leads to a surprising effect: because of superradiance, matter can hover into "floating orbits" for which the net gravitational energy loss at infinity is entirely provided by the black hole's rotational energy. Orbiting bodies remain floating until they extract sufficient angular momentum from the black hole, or until perturbations or nonlinear effects disrupt the orbit. For slowly rotating and nonrotating black holes floating orbits are unlikely to exist, but resonances at orbital frequencies corresponding to quasibound states of the scalar field can speed up the inspiral, so that the orbiting body sinks. These effects could be a smoking gun of deviations from general relativity.
119086181
Geodesic deviation in Regge calculus
Geodesic deviation is the most basic manifestation of the influence of gravitational fields on matter. We investigate geodesic deviation within the framework of Regge calculus, and compare the results with the continuous formulation of general relativity on two different levels. We show that the continuum and simplicial descriptions coincide when the cumulative effect of the Regge contributions over an infinitesimal element of area is considered. This comparison provides a quantitative relation between the curvature of the continuous description and the deficit angles of Regge calculus. The results presented might also be of help in developing generic ways of including matter terms in the Regge equations.
118984787
A NEW PROBE OF THE DISTRIBUTION OF DARK MATTER IN GALAXIES
The scale radius of dark matter halos is a critical parameter for specifying the density distribution of dark matter, and is therefore a fundamental parameter for modeling galaxies. We develop here a novel, observationally motivated probe to quantitatively infer its value within the context of the Navarro, Frenk, & White profile. We demonstrate that disturbances in the extended atomic hydrogen gas disks of galaxies can be analyzed to infer the scale radius of the dark matter halo. Our primary metric is the phase (i.e., the shape of the spiral) of the m = 1 mode of the disturbance in the outskirts of the gas disk, which we take to be produced by a tidal interaction. We apply the method to the Whirlpool galaxy, which has an optically visible satellite. We infer a scale radius of ~17 kpc for M51, which is consistent with expectations from dissipationless cosmological simulations. We explore potential degeneracies due to orbital inclination, initial conditions, satellite mass, and pericenter approach distance, and find our results to be relatively insensitive to these considerations. Our method of tracing the dark potential well through observed disturbances in outer gas disks is complementary to gravitational lensing.
118956575
Simulating Merging Galaxies: The Infrared View
We calculate multi-wavelength spectral energy distributions (SEDs) (spanning optical to millimeter wavelengths) from simulations of major galaxy mergers using a three-dimensional radiative transfer code, which treats the absorption and scattering of radiation as well as the reemission from dust grains self-consistently. These calculations allow us to deduce correlations from the X-rays to millimeter wavelengths. We confirm observed correlations for Spitzer Space Telescope’s IRAC bands, as well as correlations observed in the IRAS era. We also make predictions that should be testable by future instruments. The power of the dynamical approach afforded by calculating fluxes from the merger simulations is that we can directly correlate observed clustering in the data as seen in IRAC color-color plots with the relative amount of time the system spends in a region of color-color space. We also present photo albums spanning the lifetime of SMGs, from its infancy in the pre-merger phase to its final stage as an elliptical galaxy, as seen in various bands. Finally, we compare the SEDs from the simulations to recent observations of SMGs. Our calculations, which match observed correlations both for local ULIRGs and higher redshift systems, suggest that simulations of major mergers with black hole feedback provide an excellent framework within which to understand the emission from local ULIRGs, and their high redshift cousins, the submillimeter galaxies.
17452522
An Evolutionary Model for Submillimeter Galaxies
We calculate multi-wavelength spectral energy distributions (SEDs) (spanning optical to millimeter wavelengths) from simulations of major galaxy mergers with black hole feedback which produce submillimeter bright galaxies (SMGs), using a self-consistent three-dimensional radiative transfer code. These calculations allow us to predict multiwavelength correlations for this important class of galaxies. We review star formation rates, the time evolution of the 850 � m fluxes, along with the time evolution of the MBH Mstar relation of the SMGs formed in the mergers. We reproduce correlations for local AGN observed in Spitzer Space Telescope’s IRAC bands, and make definitive predictions for infrared X-ray correlations that should be testable by combining observations by Spitzer and the upcoming Herschel mission with X-ray surveys. To aid observational studies, we quantify the far-infrared X-ray correlations. Our dynamical approach allows us to directly correlate observed clustering in the data as seen in IRAC color-color plots with the relative amount of time the system spends in a region of color-color space. We also find that this clustering is positively correlated with the stars dominating in their contribution to the total bolometric luminosity. The merger simulations also allow us to directly correlate the 850 � m flux with the ratio of the black hole luminosity to the total luminosity, which is an inherent and testable feature of our model. We present photo albums spanning the lifetime of SMGs, from their infancy in the pre-merger phase to the final stage as an elliptical galaxy, as seen in the observed 3.6 � m and 450 � m band to visually illustrate some of the morphological differences between mergers of differing orbital inclination and progenitor redshift. We compare our SEDs from the simulations to observations of SMGs and find good agreement. We find that SMGs are a broader class of systems than starbursts or quasars. We introduce a simple, heuristic classification scheme on the basis of the LIR/Lx ratios of these galaxies, which may be interpreted qualitatively as an evolutionary scheme, as these galaxies evolve in LIR/Lx while transiting from the pre-merger stage, through the quasar phase, to a merger remnant. Subject headings: galaxies: formation—galaxies: AGN—infrared: galaxies—radiative transfer—stars: formation
119179431
AN ECCENTRICITY-MASS RELATION FOR GALAXIES FROM TIDALLY DISRUPTING SATELLITES
We infer the past orbit of the Sagittarius (Sgr) dwarf galaxy in the Milky Way halo by integrating backwards from its observed position and proper motions, including the effects of dynamical friction. Given measured proper motions, we show that there is a relation between the eccentricity (e) of Sgr’s orbit and the mass of the Milky Way (MT ) in the limit of no dynamical friction. That relation can be fit by a power-law of the form: e 0:49 MT=10 12 M -0:88 . At a fixed Milky Way mass, the dynamical friction term increases the mean eccentricity of the orbit and lowers the spread in eccentricities in proportion to the mass of the Sgr dwarf. We explore the implications of various observational constraints on Sgr’s apocenter on the e-M relation; 5 10 10 M . MSgr . 10 9 M , are precluded, for Milky Way masses 1- 2:5 10 12 M . If Belokurov et al.’s (2014) observations represent the farthest point of Sgr’s stream, then Milky Way masses in excess of 2 10 12 M are excluded forMSgr . 10 10 M . Deeper observations of Sgr’s tidal debris, from upcoming surveys such as GAIA, will allow better measurement of the Milky Way mass and of the Sgr dwarf.