arXiv subjects

Xiao-Mei Kuang

Publications and source records attributed to Xiao-Mei Kuang.

At least 91 records · Page 5Linked to original sources

arXiv2018

Axionic black branes with conformal coupling

We find neutral and charged black branes solutions with axion fields in the context of a conformally coupled gravitational theory in four dimensions. These solutions describe AdS black branes supported by axion fields that break translational invariance at the boundary, providing for momentum dissipation. The conformally coupled scalar field is regular inside and outside the event horizon and there is no need of any self-interaction, obtaining in this way solutions without fine-tuned parameters. We analyze the thermodynamics of our solutions considering the effects of the axion charges and it is shown that axionic and electric charges must be related such that the conformal scalar field does not contribute to the mass. We compute the holographic DC conductivity and we show how it is affected by the inclusion of the conformal scalar field, which provides a temperature independent behavior. We include a non-linear axionic contribution given by a k-essence term that modifies the DC conductivity providing for more general behaviors. Finally, we endorse our solutions with rotation showing that angular momentum is sustained by the axion charges.

hep-th↗

arXiv2018

The Lifshitz black branes and DC transport coefficients in massive Einstein-Maxwell-dilaton gravity

We construct analytical Lifshitz massive black brane solutions in massive Einstein-Maxwell-dilaton gravity theory. We also study the thermodynamics of these black brane solutions and obtain the thermodynamical stability conditions. On the dual nonrelativistic boundary field theory with Lifshitz symmetry, we analytically compute the DC transport coefficients, including the electric conductivity, thermoelectric conductivity, and thermal conductivity. The novel property of our model is that the massive term supports the Lifshitz black brane solutions with $z\neq 1$ in such a way that the DC transport coefficients in the dual field theory are finite. We also find that the Wiedemann-Franz law in this dual boundary field theory is violated, which indicates that it may involve strong interactions.

hep-th↗

arXiv2017

The quantum effect on Friedmann equation in FRW universe

We study the modified Friedmann equation in the Friedmann-Robertson-Walker universe with quantum effect. Our modified results mainly stem from the new entropy-area relation and the novel idea of T. Padmanabhan, who considers the cosmic space to be emerged from the cosmic time progresses, so that the expansion rate of the universe is determined by the difference of degrees of freedom between the holographic surface and the bulk inside. We also discuss the possibility of having bounce cosmological solution from the modified Friedmann equation in spatially flat geometry.

gr-qc↗

arXiv2017

Holographic heat engine with momentum relaxation

We investigate the heat engine defined via black hole with momentum relaxation, which is introduced by massless axion fields. We first study the extended thermodynamical properties of the black hole and then apply it to define a heat engine. Then, we analyze how the momentum relaxation affects the efficiency of the heat engine in the limit of high temperature. We find that depending on the schemes of specified parameters in the engine circle, the influence of momentum relaxation on the efficiency of the heat engine behaves novelly, and the qualitative behaviors do depend on the dimension of the gravity theory.

hep-th↗

arXiv2017

The Effect of the Gauss-Bonnet term to Hawking Radiation from arbitrary dimensional Black Brane

We investigate the probabilities of the tunneling and the radiation spectrums of the massive spin-1 particles from arbitrary dimensional Gauss-Bonnet-Axions (GBA) Anti-de Sitter (AdS) black brane, via using the WKB approximation to the Proca spin-1 field equation. The tunneling probabilities and Hawking temperature of the arbitrary dimensional GBA AdS black brane is calculated via the Hamilton-Jacobi approach. We also compute the Hawking temperature via Parikh-Wilczek tunneling approach. The results obtained from the two methods are consistent. In our setup, the Gauss-Bonnet (GB) coupling affects the Hawking temperature if and only if the momentum of axion fields is non-vanishing.

gr-qc↗

arXiv2017

Thermal transport and quasi-normal modes in Gauss-Bonnet-axions theory

We obtain the black brane solution in arbitrary dimensional Gauss-Bonnet-axions (GBA) gravity theory. And then the thermal conductivity of the boundary theory dual to this neutral black brane is explored. We find that the momentum dissipation suppresses the DC thermal conductivity while it is enhanced by larger GB parameter. The analytical and numerical results of DC thermal conductivity match very well. Also we study the effect of the momentum dissipation and the GB coupling on the AC thermal conductivity and fit the results by Drude-like behavior for low frequency. Finally, we analytical compute the quasi-normal modes (QNM) frequency of the perturbative master field in large dimensions limit. Our analytical QNM frequencies agree well with the numerical results in large enough finite dimensions.

hep-th↗

arXiv2017

Charged Lifshitz black hole and probed Lorentz-violation fermions from holography

We analytically obtain a new charged Lifshtitz solution by adding a non-relativistic Maxwell field in Horava-Lifshitz gravity. The black hole exhibits an anisotropic scaling between space and time (Lifshitz scaling) in the UV limit, while in the IR limit, the Lorentz invariance is recovered. We introduce the probed Lorentz-violation fermions into the background and holographically investigate the spectral properties of the dual fermionic operator. The Lorentz-violation of fermions will enhance the peak and corresponds larger fermi momentum, which compensates the non-relativistic bulk effect of the dynamical exponent. For a fixed $z$, when the Lorentz-violation of fermions increases to a critical value, the behavior of the low energy excitation goes from a non-Fermi liquid type to a fermi liquid type, which implies a kind of phase transition.

hep-th↗

arXiv2017

Thermal phase transitions of dimensionally continued AdS black holes

We study the thermal phase transitions of charged black holes in dimensionally continued gravity in anti-de Sitter space. We find the van der Waals-like phase transition in the temperature-entropy plane of the black holes with spherical horizons in even dimensions, and there is no such phase transition of the black holes with flat and hyperbolic geometries. Near the critical inflection point, the critical exponent is computed and its value does not depend on the dimension. The Maxwell equal area law is checked to be fulfilled in the temperature-entropy diagram for the first order phase transition. In odd dimensions, there are no thermal phase transitions for the black hole with any geometry of the horizon.

hep-th↗

arXiv2016

Building a Holographic Superconductor with a Scalar Field Coupled Kinematically to Einstein Tensor

We study the holographic dual description of a superconductor in which the gravity sector consists of a Maxwell field and a charged scalar field which except its minimal coupling to gravity it is also coupled kinematically to Einstein tensor. As the strength of the new coupling is increased, the critical temperature below which the scalar field condenses is lowering, the condensation gap decreases faster than the temperature, the width of the condensation gap is not proportional to the size of the condensate and at low temperatures the condensation gap tends to zero for the strong coupling. These effects which are the result of the presence of the coupling of the scalar field to the Einstein tensor in the gravity bulk, provide a dual description of impurities concentration in a superconducting state on the boundary.

hep-th↗

arXiv2016

Lifshitz holographic superconductor in Horava-Lifshitz gravity

We study the holographic phase transition of superconductor dual to a Lifshitz black brane probed by an anisotropic scalar field in the probe limit in Hourava-Lifshitz gravity. With the use of numerical and analytical method, we investigate how the critical temperature of the condensation is affected by the Lifshitz exponent $z$, $α-$correction term in the action as well as the dimensions of the gravity. We also numerically explore the condensation of the dual operator and optical conductivity of the holographic system. Various interesting properties of the holographic condensation affected by the parameters of model are discussed.

hep-th↗

arXiv2016

Topological black holes in pure Gauss-Bonnet gravity and phase transitions

We study charged, static, topological black holes in pure Gauss-Bonnet gravity in asymptotically AdS space. As in general relativity, the theory possesses a unique nondegenerate AdS vacuum. It also admits charged black hole solutions which asymptotically behave as the Reissner-Nordström AdS black hole. We discuss black hole thermodynamics of these black holes. Then we study phase transitions in a dual quantum field theory in four dimensions, with the Stückelberg scalar field as an order parameter. We find in the probe limit that the black hole can develop hair below some critical temperature, which suggests a phase transition. Depending on the scalar coupling constants, the phase transition can be first or second order. Analysis of the free energy reveals that, comparing the two solutions, the hairy state is energetically favorable, thus a phase transition will occur in a dual field theory.

hep-th↗

arXiv2015

Scalar Boundary Conditions in Hyperscaling Violating Geometry

We study the possible boundary conditions of scalar field modes in a hyperscaling violation(HV) geometry with Lifshitz dynamical exponent $z (z\geqslant1)$ and hyperscaling violation exponent $θ(θ\neq0)$. For the case with $θ>0$, we show that in the parameter range with $1\leq z\leq 2,~-z+d-1<θ\leq (d-1)(z-1)$ or $z>2,~-z+d-1<θ\leq d-1$, the boundary conditions have different types, including the Neumann, Dirichlet and Robin conditions, while in the range with $θ\leq-z+d-1$, only Dirichlet type condition can be set. In particular, we further confirm that the mass of the scalar field does not play any role in determining the possible boundary conditions for $θ>0$, which has been addressed in Ref. \cite{1201.1905}. Meanwhile, we also do the parallel investigation in the case with $θ<0$. We find that for $m^2<0$, three types of boundary conditions are available, but for $m^2>0$, only one type is available.

hep-th↗

arXiv2015

Fermionic phase transition induced by the effective impurity in holography

We investigate the holographic fermionic phase transition induced by the effective impurity in holography, which is introduced by massless scalar fields in Einstein-Maxwell-massless scalar gravity. We obtain a phase diagram in $(α, T)$ plane separating the Fermi liquid phase and the non-Fermi liquid phase.

hep-th↗

arXiv2015

Transport coefficients from hyperscaling violating black brane: shear viscosity and conductivity

We investigate two transport coefficients, shear viscosity and conductivity, in a non-relativistic boundary filed theory without hyperscaling symmetry, which is dual to a bulk charged hyperscaling violating black brane. Employing matching method, we obtain that the ratio of shear viscosity and the entropy density is alway $1/4π$ at any temperature, which satisfies the Kovtun-Starinets-Son (KSS) bound. Besides, we also present the universal formulas of AC conductivity, which is closely dependent on the relation between geometrical parameters $z$ and $θ$. The optical conductivity at high frequency limit behaves with a (non)-power law scaling or approaches to be constant, depending on the choice of $z$ and $θ$. This feature is different from the observes in Lifshitz black brane that the optical conductivity always complies with a (non)-power law scaling in high frequency limit when the Lifshitz exponent $z>1$. We also argue that the temperate has no print on the exponent of (non)-power law scaling in large frequency while it will affect the strength of conductivity at low frequency.

hep-th↗

arXiv2015

Dynamically generated gap from holography in the charged black brane with hyperscaling violation

We holographically investigate the effects of a dipole coupling between a fermion field and a $U(1)$ gauge field on the dual fermionic sector in the charged gravity bulk with hyperscaling violation. We analytically study the features of the ultraviolet and infrared Green's functions of the dual fermionic system and we show that as the dipole coupling and the hyperscaling violation exponent are varied, the fluid possess Fermi, marginal Fermi, non-Fermi liquid phases and also an additional Mott insulating phase. We find that the increase of the hyperscaling violation exponent which effectively reduces the dimensionality of the system makes it harder for the Mott gap to be formed. We also show that the observed duality between zeros and poles in the presence of a dipole moment coupling still persists in theories with hyperscaling violation.

hep-th↗

arXiv2014

Formation of Fermi surfaces and the appearance of liquid phases in holographic theories with hyperscaling violation

We consider a holographic fermionic system in which the fermions are interacting with a U(1) gauge field in the presence of a dilaton field in a gravity bulk of a charged black hole with hyperscaling violation. Using both analytical and numerical methods, we investigate the properties of the infrared and ultaviolet Green's functions of the holographic fermionic system. Studying the spectral functions of the system, we find that as the hyperscaling violation exponent is varied, the fermionic system possesses Fermi, non-Fermi, marginal-Fermi and log-oscillating liquid phases. Various liquid phases of the fermionic system with hyperscaling violation are also generated with the variation of the fermionic mass. We also explore the properties of the flat band and the Fermi surface of the non-relativistic fermionic fixed point dual to the hyperscaling violation gravity.

hep-th↗

arXiv2014

Entanglement Entropy as a Probe of the Proximity Effect in Holographic Superconductors

We study the entanglement entropy as a probe of the proximity effect of a superconducting system by using the gauge/gravity duality in a fully back-reacted gravity system. While the entanglement entropy in the superconducting phase is less than the entanglement entropy in the normal phase, we find that near the contact interface of the superconducting to normal phase the entanglement entropy has a different behavior due to the leakage of Cooper pairs to the normal phase. We verify this behavior by calculating the conductivity near the boundary interface.

hep-th↗

arXiv2013

Holographic fermions with running chemical potential and dipole coupling

We explore the properties of the holographic fermions in extremal $R$-charged black hole background with a running chemical potential, as well as the dipole coupling between fermions and the gauge field in the bulk. We find that although the running chemical potential effect the location of the Fermi surface, it does not change the type of fermions. We also study the onset of the Fermi gap and the gap effected by running chemical potential and the dipole coupling. The spectral function in the limit $ω\rightarrow0$ and the existence of the Fermi liquid are also investigated. The running chemical potential and the dipole coupling altogether can make a non-Fermi liquid become the Landau-Fermi type.

hep-th↗