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Yi Ling

Publications and source records attributed to Yi Ling.

At least 91 records · Page 5Linked to original sources
arXiv2013

Fluid/Gravity Correspondence For General Non-rotating Black Holes

In this paper, we investigate the fluid/gravity correspondence in spacetime with general non-rotating weakly isolated horizon. With the help of Petrov-like boundary condition and large mean curvature limit, we show that the dual hydrodynamical system is described by a generalized forced incompressible Navier-Stocks equation. Specially, for stationary black holes or those spacetime with some asymptotically stationary conditions, such a system reduces to a standard forced Navier-Stocks system.

hep-th↗
arXiv2012

Magnetohydrodynamics from gravity

Imposing the Petrov-like boundary condition on the hypersurface at finite cutoff, we derive the hydrodynamic equation on the hypersurface from the bulk Einstein equation with electromagnetic field in the near horizon limit. We first get the general framework for spacetime with matter field, and then derive the incompressible Navier-Stokes equations for black holes with electric charge and magnetic charge respectively. Especially, in the magnetic case, the standard magnetohydrodynamic equations will arise due to the existence of the background electromagnetic field on the hypersurface.

hep-th↗
arXiv2012

Fluid/gravity duality with Petrov-like boundary condition in a spacetime with a cosmological constant

Recently it has been shown that imposing Petrov type I condition on the boundary may reduce the Einstein's equation to the Navier-Stokes equation in the non-relativistic and near-horizon limit. In this paper we extend this framework to a spacetime with a cosmological constant. By explicit construction we show that the Navier-Stokes equation can be derived from both black brane background and spatially curved spacetime. We also conjecture that imposing Petrov type I condition on the boundary should be equivalent to the conventional method using the hydrodynamical expansion of the metric in the near horizon limit.

hep-th↗
arXiv2012

Incompressible Navier-Stokes Equation from Einstein-Maxwell and Gauss-Bonnet-Maxwell Theories

The dual fluid description for a general cutoff surface at radius r=r_c outside the horizon in the charged AdS black brane bulk space-time is investigated, first in the Einstein-Maxwell theory. Under the non-relativistic long-wavelength expansion with parameter ε, the coupled Einstein-Maxwell equations are solved up to O(ε^2). The incompressible Navier-Stokes equation with external force density is obtained as the constraint equation at the cutoff surface. For non-extremal black brane, the viscosity of the dual fluid is determined by the regularity of the metric fluctuation at the horizon, whose ratio to entropy density η/s is independent of both the cutoff r_c and the black brane charge. Then, we extend our discussion to the Gauss-Bonnet-Maxwell case, where the incompressible Navier-Stokes equation with external force density is also obtained at a general cutoff surface. In this case, it turns out that the ratio η/s is independent of the cutoff r_c but dependent on the charge density of the black brane.

hep-th↗
arXiv2012

Holographic p-wave Superconductors in Quasi-topological Gravity

We construct a holographic p-wave superconductor model in the framework of quasi-topological gravity in the probe limit. The relation between the critical temperature and the coupling parameters of higher curvature terms is investigated. The numerical results for conductivity are presented as well. It turns out that our data fits the Drude model very well in the low frequency limit, and the values of DC conductivity as well as the relaxation time are obtained numerically.

hep-th↗
arXiv2012

Holographic RG flows and transport coefficients in Einstein-Gauss-Bonnet-Maxwell theory

We apply the membrane paradigm and the holographic Wilsonian approach to the Einstein-Gauss-Bonnet-Maxwell theory. The transport coefficients for a quark-gluon plasma living on the cutoff surface are derived in a spacetime of charged black brane. Because of the mixing of the Gauss-Bonnet coupling and the Maxwell fields, the vector modes/shear modes of the metric and Maxwell fluctuations turn out to be very difficult to decouple. We firstly evaluate the AC conductivity at a finite cutoff surface by solving the equation of motion numerically, then manage to derive the radial flow of DC conductivity with the use of the Kubo formula. It turns out that our analytical results match the numerical data in low frequency limit very well. The diffusion constant $D(u_c)$ is also derived in a long wavelength expansion limit. We find it depends on the Gauss-Bonnet coupling as well as the position of the cutoff surface.

hep-th↗
arXiv2011

From Petrov-Einstein to Navier-Stokes in Spatially Curved Spacetime

We generalize the framework in arXiv:1104.5502 to the case that an embedding may have a nonvanishing intrinsic curvature. Directly employing the Brown-York stress tensor as the fundamental variables, we study the effect of finite perturbations of the extrinsic curvature while keeping the intrinsic metric fixed. We show that imposing a Petrov type I condition on the hypersurface geometry may reduce to the incompressible Navier-Stokes equation for a fluid moving in spatially curved spacetime in the near-horizon limit.

gr-qc↗
arXiv2010

Holographic Superconductors in Quasi-topological Gravity

In this paper we study (3+1) dimensional holographic superconductors in quasi-topological gravity which is recently proposed by R. Myers {\it et.al.}. Through both analytical and numerical analysis, we find in general the condensation becomes harder with the increase of coupling parameters of higher curvature terms. In particular, comparing with those in ordinary Gauss-Bonnet gravity, we find that positive cubic corrections in quasi-topological gravity suppress the condensation while negative cubic terms make it easier. We also calculate the conductivity numerically for various coupling parameters. It turns out that the universal relation of $ω_g/T_c\simeq 8$ is unstable and this ratio becomes larger with the increase of the coupling parameters. A brief discussion on the condensation from the CFT side is also presented.

hep-th↗
arXiv2010

The cosmological perturbation theory in loop cosmology with holonomy corrections

In this paper we investigate the scalar mode of first-order metric perturbations over spatially flat FRW spacetime when the holonomy correction is taken into account in the semi-classical framework of loop quantum cosmology. By means of the Hamiltonian derivation, the cosmological perturbation equations is obtained in longitudinal gauge. It turns out that in the presence of metric perturbation the holonomy effects influence both background and perturbations, and contribute the non-trivial terms $S_{h1}$ and $S_{h2}$ in the cosmological perturbation equations.

hep-th↗
arXiv2010

The Big Bounce in Rainbow Universe

The usual Einstein's equations is modified as a one parameter family of equations in the framework of rainbow gravity. In this paper we derive the modified Friedmann-Robertson-Walker (FRW) equations when the cosmological evolution of radiation particles is taken into account. In particular, given some specific dispersion relations, the big bounce solutions to the modified FRW equations can be derived. Notably, to obtain a well defined rainbow metric at the moment of the big bounce, we find it seems necessary to introduce a cosmological constant which depends on the energy of probes as well, implying that a universe with a positive cosmological constant more likely undergoes a big bounce at least at this phenomenological level.

gr-qc↗
arXiv2010

Thermal fluctuations in viscous cosmology

In this paper we investigate the power spectrum of thermal fluctuations in very early stage of viscous cosmology. When the state parameter as well as the viscous coefficient of a barotropic fluid is properly chosen, a scale invariant spectrum with large non-Gaussianity can be obtained. In contrast to the results previously obtained in string gas cosmology and holographic cosmology, we find the non-Gaussianity in this context can be k-independent such that it is not suppressed at large scale, which is expected to be testified in future observation.

gr-qc↗
arXiv2010

On thermal force from holographic action

Applying the relation between Euclidean on-shell action in the bulk and free energy on the holographic screen to a test charged particle in the charged R-N black hole, we show that not only gravity but also electromagnetic force can be regarded as a sort of thermal force, which accomplishes the unification of gravity and electromagnetism to some extent. In addition, taking into account the fact that both the temperature and thermal force of the dual system are measured at infinity, we argue that the dual holographic screen may be located at infinity.

gr-qc↗
arXiv2010

A note on entropic force and brane cosmology

Recently Verlinde proposed that gravity is an entropic force caused by information changes when a material body moves away from the holographic screen. In this note we apply this argument to brane cosmology, and show that the cosmological equation can be derived from this holographic scenario.

hep-th↗
arXiv2010

Thermal non-Gaussianity in Near-Milne universe

The thermal non-Gaussianity in Near-Milne universe is investigated in this letter. Through classifying thermal fluctuations into two types, one characterized by a phase transition and the other without phase transition, we show that for fluctuations undergoing a phase transition, the non-Gaussianity depends linearly on $k$, but in non-phase transition case it is proportional to $k^{-3γ},γ>0$. Moreover, if the phase transition scenario is similar to that in holographic cosmology, we find that the non-Gaussianity $f_{NL}^{equil}$ can reach ${\cal O}(1)$ or larger than ${\cal O}(1)$ by fine tuning of the equation of state $ω_{C}$. Especially at the limit of $ω_{C}\to -5/3$, the non-Gaussianity can be very large. On the other hand, for non-phase transition case, the non-Gaussianity estimator $f_{NL}^{equil}$ is approximately $f_{NL}^{equil}\simeq 5/108$ when the energy is sub-extensive, especially when $γ\to 0^{+}$. However, when $γ\to 4$, large non-Gaussianity can be obtained.

hep-th↗
arXiv2009

Bouncing universe from a modified dispersion relation

In this paper we argue that modified Friedmann equations with a bounce solution can be derived from a modified dispersion relation by employing a thermodynamical description of general relativity on the apparent horizon.

gr-qc↗
arXiv2009

Viscous gravitational aether and the cosmological constant problem

Recently a notion of gravitational aether is advocated to solve the cosmological constant problem.Through the modification of the source of gravity one finds that the effective Newton's constant is source dependent so as to provide a simple but consistent way to decouple gravity from the vacuum energy.However,in the original paper the ratio of the effective Newton's constants for pressureless dust and radiation has an upper bound which is 0.75.In this paper we propose a scheme to loose this bound by introducing a bulk viscosity for the gravitational aether,and expect this improvement will provide more space for matching predictions from this theoretical programm with observational constraints.

gr-qc↗
arXiv2009

Modified (A)dS Schwarzschild black holes in Rainbow spacetime

A modified (Anti-)de Sitter Schwarzschild black hole solution is presented in the framework of rainbow gravity with a cosmological constant. Its thermodynamical properties are investigated. In general the temperature of modified black holes is dependent on the energy of probes which take the measurement. However, a notion of intrinsic temperature can be introduced by identifying these probes with radiation particles emitted from black holes. It is interesting to find that the Hawking temperature of this sort of black holes can be reproduced by employing the extended uncertainty principle and modified dispersion relations to the ordinary (A)dS Schwarzschild black holes.

gr-qc↗