Effective Action for D-branes on SU(2)/U(1) Gauged WZW Model

Dynamics of D-branes on $SU(2)/U(1)$ gauged WZW model are investigated. We find the effective action for infinite $k$, where $k$ is the level of WZW model. We also consider finite $k$ correction to the effective action which is compatible with Fedosov's deformation quantization of the background.Comment: 12 pages, Latex file. v2: Acknowledgement added. to appear in Phys. Lett.

The stability and gravitational Newtonian limit of a modified Randall-Sundrum model

For a modified Randall-Sundrum model [Phys. Rev. D 88 (2013) 025048], the graviton equations are derived and the mass spectrum found. The latter includes a massless graviton and a continuum mass with a gap. There is no negative mass-squared in the spectrum, so the model is stable. The gravitational Newtonian limit is obtained with an exponentially suppressed modification from extra dimension.Comment: 10 page

Entanglement entropy of singular surfaces under relevant deformations in holography

In the vacuum state of a CFT, the entanglement entropy of singular surfaces contains a logarithmic universal term which is only due to the singularity of the entangling surface. We consider the relevant perturbation of a three dimensional CFT for singular entangling surface. We observe that in addition to the universal term due to the entangling surface, there is a new logarithmic term which corresponds to a relevant perturbation of the conformal field theory with a coefficient depending on the scaling dimension of the relevant operator. We also find a new power law divergence in the holographic entanglement entropy. In addition, we study the effect of a relevant perturbation in the Gauss-Bonnet gravity for a singular entangling surface. Again a logarithmic term shows up. This new term is proportional to both the dimension of the relevant operator and the Gauss-Bonnet coupling. We also introduce the renormalized entanglement entropy for a kink region which in the UV limit reduces to a universal positive finite term.Comment: 21 pages. v2: 30 pages, title changed, one section regarding the renormalization added, minor corrections in text and equation

Non-Commutative Instantons and the Information Metric

By using the so-called Information Metric on the moduli space of an anti-selfdual (ASD) Instanton in a Self-Dual (SD) Non-Commutative background, we investigate the geometry of moduli space. The metric is evaluated perturbatively in non-commutativity parameter and we show that by putting a cut-off in the location of instanton in the definition of Information Metric we can recover the five dimensional space time in the presence of a B-field. This result shows that the non-commutative YM-Instanton Moduli corresponds to D-Instanton Moduli in the gravity side where the radial and transverse location of D-Instanton are corresponding to YM-Instanton size and location, respectively. The match is shown in the first order of non-commutativity parameter.Comment: latex. v2) 14 pages, keywords and references added, to appear in MPL

Curved Corner Contribution to the Entanglement Entropy in an Anisotropic Spacetime

We study the holographic entanglement entropy of anisotropic and nonconformal theories that are holographically dual to geometries with hyperscaling violation, parameterized by two parameters $z$ and $\theta$. In the vacuum state of a conformal field theory, it is known that the entanglement entropy of a kink region contains a logarithmic universal term which is only due to the singularity of the entangling surface. But, we show that the effects of the singularity as well as anisotropy of spacetime on the entanglement entropy exhibit themselves in various forms depending on $z$ and $\theta$ ranges. We identify the structure of various divergences that may be appear in the entanglement entropy, specially those which give rise to a universal contribution in the form of the logarithmic or double logarithmic terms. In the range $z>1$, for values $z=2k/(2k-1)$ with some integer $k$ and $\theta=0$, Lifshitz geometry, we find a double logarithmic term. In the range $0<z$, for values $\theta=1-2n|z-1|$ with some integer $n$ we find a logarithmic term.Comment: 19 pages, 2 figs; v2: introduction and conclusion expanded, refs adde

Holographic Aspects of a Higher Curvature Massive Gravity

We study the holographic dual of a massive gravity with Gauss-Bonnet and cubic quasi-topological higher curvature terms. Firstly, we find the energy-momentum two-point function of the 4-dimensional boundary theory where the massive term breaks the conformal symmetry as expected. An $a$-theorem is introduced based on the null energy condition. Then we focus on a black brane solution in this background and derive the ratio of shear viscosity to entropy density for the dual theory. It is worth mentioning that the concept of viscosity as a transport coefficient is obscure in a nontranslational invariant theory as in our case. So although we use the Green-Kubo's formula to derive it, we rather call it the rate of entropy production per the Planckian time due to a strain. Results smoothly cover the massless limit.Comment: v2: 20 pages, typo corrected, references added; v3: section 2.2 revised; v4: section 2.2 modified, viscosity formula revised, 2 figs added, references added; v5: 23 pages, a sign mistake in eq. (74) fixed (results modified), eq. (34) modified, one fig added, refs added, to appear in EPJ