44 research outputs found
Effective Action for D-branes on SU(2)/U(1) Gauged WZW Model
Dynamics of D-branes on gauged WZW model are investigated. We
find the effective action for infinite , where is the level of WZW
model. We also consider finite 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
Graviton Propagation in an Asymmetric Warped Background: Lorentz Violation and the Null Energy Condition
The graviton propagation in an asymmetric background is studied. The
background is a configuration in the six-dimensional Salam-Sezgin model, in
which a 3-form H-field turned on [JHEP 0910(2009)086]. The compact dimensions
form a cylindrical space with branes as boundaries. The background gets
asymmetry due to the H-field and violates the Lorentz symmetry. We derive the
graviton equation in this background and show that it gets massless mode
traveling with superluminal speed. A tower of K-K modes exists with a mass gap.
On the other hand, it is known that breaking the Lorentz symmetry on an
asymmetric background is constrained by the null energy condition. This no-go
theorem doesn't work well in six-dimensional space-times and by this model we
provide a counterexample for which the null energy condition is satisfied while
the Lorentz symmetry is gravitationally violated.Comment: 20 pages, 1 figure. v2: published version, more phenomenological
discussions added, references added, numerical error fixe
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 and . 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 and 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 , for values with some integer and ,
Lifshitz geometry, we find a double logarithmic term. In the range , for
values with some integer 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 -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