9,796 research outputs found
pp Wave Big Bangs: Matrix Strings and Shrinking Fuzzy Spheres
We find pp wave solutions in string theory with null-like linear dilatons.
These provide toy models of big bang cosmologies. We formulate Matrix String
Theory in these backgrounds. Near the big bang ``singularity'', the string
theory becomes strongly coupled but the Yang-Mills description of the matrix
string is weakly coupled. The presence of a second length scale allows us to
focus on a specific class of non-abelian configurations, viz. fuzzy cylinders,
for a suitable regime of parameters. We show that, for a class of pp waves,
fuzzy cylinders which start out big at early times dynamically shrink into
usual strings at sufficiently late times.Comment: 29 pages, ReVTeX and AMSLaTeX. 4 Figures. v2: Typo corrected and
reference adde
27/32
We show that when an N=2 SCFT flows to an N=1 SCFT via giving a mass to the
adjoint chiral superfield in a vector multiplet with marginal coupling, the
central charges a and c of the N=2 theory are related to those of the N=1
theory by a universal linear transformation. In the large N limit, this
relationship implies that the central charges obey a_IR/a_UV=c_IR/c_UV=27/32.
This gives a physical explanation to many examples of this number found in the
literature, and also suggests the existence of a flow between some theories not
previously thought to be connected.Comment: 3 pages. v2: references added, minor typos correcte
Born-Infeld Type Extension of (Non-)Critical Gravity
We consider the Born-Infeld type extension of (non-)critical gravity which is
higher curvature gravity on Anti de-Sitter space with specific combinations of
scalar curvature and Ricci tensor. This theory may also be viewed as a natural
extension of three-dimensional Born-Infeld new massive gravity to arbitrary
dimensions. We show that this extension is consistent with holographic
-theorem and scalar graviton modes are absent in this theory. After showing
that ghost modes in the theory can be truncated consistently by appropriate
boundary conditions, we argue that the theory is classically equivalent to
Einstein gravity at the non-linear level. Black hole solutions are discussed in
the view point of the full non-linear classical equivalence between the theory
and Einstein gravity. Holographic entanglement entropy in the theory is also
briefly commented on.Comment: 1+13 pages, improvements in presentation, references added, accepted
to PR
Holographic Dual of BCFT
We propose a holographic dual of a conformal field theory defined on a
manifold with boundaries, i.e. boundary conformal field theory (BCFT). Our new
holography, which may be called AdS/BCFT, successfully calculates the boundary
entropy or g-function in two dimensional BCFTs and it agrees with the finite
part of the holographic entanglement entropy. Moreover, we can naturally derive
a holographic g-theorem. We also analyze the holographic dual of an interval at
finite temperature and show that there is a first order phase transition.Comment: 5 pages, 3 figs, a reference added, typos corrected, to be published
in PR
Comparative Planetary Atmospheres: Models of TrES-1 and HD209458b
We present new self-consistent atmosphere models for transiting planets
TrES-1 and HD209458b. The planets were recently observed with the Spitzer Space
Telescope in bands centered on 4.5 and 8.0 m, for TrES-1, and 24 m,
for HD209458b. We find that standard solar metallicity models fit the
observations for HD209458b. For TrES-1, which has an T_eff ~300 K cooler, we
find that models with a metallicity 3-5 times enhanced over solar abundances
can match the 1 error bar at 4.5 m and 2 at 8.0m.
Models with solar abundances that included energy deposition into the
stratosphere give fluxes that fall within the 2 error bars in both
bands. The best-fit models for both planets assume that reradiation of absorbed
stellar flux occurs over the entire planet. For all models of both planets we
predict planet/star flux ratios in other Spitzer bandpasses.Comment: Accepted to the Astrophysical Journal Letters, May 17, 200
Three flavour Quark matter in chiral colour dielectric model
We investigate the properties of quark matter at finite density and
temperature using the nonlinear chiral extension of Colour Dielectric Model
(CCM). Assuming that the square of the meson fields devlop non- zero vacuum
expectation value, the thermodynamic potential for interacting three flavour
matter has been calculated. It is found that remain zero
in the medium whereas changes in the medium. As a result, and
quark masses decrease monotonically as the temperature and density of the quark
matter is increased.In the present model, the deconfinement density and
temperature is found to be lower compared to lattice results. We also study the
behaviour of pressure and energy density above critical temperature.Comment: Latex file. 5 figures available on request. To appear in Phys. Rev.
Seeing a c-theorem with holography
There is no known model in holography exhibiting a -theorem where the
central charges of the dual CFT are distinct. We examine a holographic model of
RG flows in a framework where the bulk gravity theory contains higher curvature
terms. The latter allows us to distinguish the flow of the central charges
and in the dual field theories in four dimensions. One finds that the flow
of is naturally monotonic but that of is not. Extending the analysis of
holographic RG flows to higher dimensions, we are led to formulate a novel
c-theorem in arbitrary dimensions for a universal coefficient appearing in the
entanglement entropy of the fixed point CFT's.Comment: 5 pages, 1 figure, v2: minor change
The group approach to AdS space propagators: A fast algorithm
In this letter we show how the method of [4] for the calculation of two-point
functions in d+1-dimensional AdS space can be simplified. This results in an
algorithm for the evaluation of the two-point functions as linear combinations
of Legendre functions of the second kind. This algorithm can be easily
implemented on a computer. For the sake of illustration, we displayed the
results for the case of symmetric traceless tensor fields with rank up to l=4.Comment: 14 pages, comment adde
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