86 research outputs found
Euclidean wormholes with Phantom field and Phantom field accompanied by perfect fluid
We study the classical Euclidean wormhole solutions for the gravitational
systems with minimally coupled pure Phantom field and minimally coupled Phantom
field accompanied by perfect fluid. It is shown that such solutions do exist
and then the general forms of the Phantom field potential are obtained for
which there are classical Euclidean wormhole solutions.Comment: 15 pages, major revision with perfect flui
Casimir Effect, Achucarro-Ortiz Black Hole and the Cosmological Constant
We treat the two-dimensional Achucarro-Ortiz black hole (also known as (1+1)
dilatonic black hole) as a Casimir-type system. The stress tensor of a massless
scalar field satisfying Dirichlet boundary conditions on two one-dimensional
"walls" ("Dirichlet walls") is explicitly calculated in three different vacua.
Without employing known regularization techniques, the expression in each
vacuum for the stress tensor is reached by using the Wald's axioms. Finally,
within this asymptotically non-flat gravitational background, it is shown that
the equilibrium of the configurations, obtained by setting Casimir force to
zero, is controlled by the cosmological constant.Comment: 20 pages, LaTeX, minor corrections, comments and clarifications
added, version to appear in Phys. Rev.
Strings on conifolds from strong coupling dynamics, part I
A method to solve various aspects of the strong coupling expansion of the
superconformal field theory duals of AdS_5 x X geometries from first principles
is proposed. The main idea is that at strong coupling the configurations that
dominate the low energy dynamics of the field theory compactified on a three
sphere are given by certain non-trivial semi-classical configurations in the
moduli space of vacua.
We show that this approach is self-consistent and permits one to express most
of the dynamics in terms of an effective N=4 SYM dynamics. This has the
advantage that some degrees of freedom that move the configurations away from
moduli space can be treated perturbatively, unifying the essential low energy
dynamics of all of these theories. We show that with this formalism one can
compute the energies of strings in the BMN limit in the Klebanov-Witten theory
from field theory considerations, matching the functional form of results found
using AdS geometry. This paper also presents various other technical results
for the semiclassical treatment of superconformal field theories.Comment: 52 pages, JHEP3 styl
D-Brane Effective Actions and Particle Production near the Beginning of the Tachyon Condensation
In this paper we will study the quantum field theory of fluctuation modes
around the classical solution that describes tachyon condensation on unstable
D-brane.We will calculate the number of particle produced near the beginning of
the rolling tachyon process. We will perform this calculation for different
tachyon effective actions and we will find that the rate of the particle
production strongly depends on the form of the effective action used for the
description of the early stage of the tachyon condensation.Comment: 21 page
Revised spherically symmetric solutions of gravity
We study spherically symmetric static empty space solutions in
model of gravity. We show that the Schwarzschild
metric is an exact solution of the resulted field equations and consequently
there are general solutions which {are perturbed Schwarzschild metric and
viable for solar system. Our results for large scale contains a logarithmic
term with a coefficient producing a repulsive gravity force which is in
agreement with the positive acceleration of the universe.Comment: 8 page
Energy Conditions in Modified Gravity with Non-minimal Coupling to Matter
In this paper we study a model of modified gravity with non-minimal coupling
between a general function of the Gauss-Bonnet invariant, , and matter
Lagrangian from the point of view of the energy conditions. Such model has been
introduced in Ref. [21] for description of early inflation and late-time cosmic
acceleration. We present the suitable energy conditions for the above mentioned
model and then, we use the estimated values of the Hubble, deceleration and
jerk parameters to apply the obtained energy conditions to the specific class
of modified Gauss-Bonnet models.Comment: 12 pages, no figur, Accepted for publication in Astrophysics and
Space Scienc
Dynamics of Warped Flux Compactifications
We discuss the four dimensional effective action for type IIB flux
compactifications, and obtain the quadratic terms taking warp effects into
account. The analysis includes both the 4-d zero modes and their KK
excitations, which become light at large warping. We identify an `axial' type
gauge for the supergravity fluctuations, which makes the four dimensional
degrees of freedom manifest. The other key ingredient is the existence of
constraints coming from the ten dimensional equations of motion. Applying these
conditions leads to considerable simplifications, enabling us to obtain the low
energy lagrangian explicitly. In particular, the warped K\"ahler potential for
metric moduli is computed and it is shown that there are no mixings with the KK
fluctuations and the result differs from previous proposals. The four
dimensional potential contains a generalization of the Gukov-Vafa-Witten term,
plus usual mass terms for KK modes.Comment: 37 pages. v2. References added, typos corrected. v3. Matches JHEP
versio
Implications of Space-Time foam for Entanglement Correlations of Neutral Kaons
The role of invariance and consequences for bipartite entanglement of
neutral (K) mesons are discussed. A relaxation of leads to a modification
of the entanglement which is known as the effect. The relaxation of
assumptions required to prove the theorem are examined within the context
of models of space-time foam. It is shown that the evasion of the EPR type
entanglement implied by (which is connected with spin statistics) is
rather elusive. Relaxation of locality (through non-commutative geometry) or
the introduction of decoherence by themselves do not lead to a destruction of
the entanglement. So far we find only one model which is based on non-critical
strings and D-particle capture and recoil that leads to a stochastic
contribution to the space-time metric and consequent change in the neutral
meson bipartite entanglement. The lack of an omega effect is demonstrated for a
class of models based on thermal like baths which are generally considered as
generic models of decoherence
On The Problem of Particle Production in c=1 Matrix Model
We reconsider and analyze in detail the problem of particle production in the
time dependent background of matrix model where the Fermi sea drains away
at late time. In addition to the moving mirror method, which has already been
discussed in hep-th/0403169 and hep-th/0403275, we describe yet another method
of computing the Bogolubov coefficients which gives the same result. We
emphasize that these Bogolubov coefficients are approximately correct for small
value of the deformation parameter.
We also study the time evolution of the collective field theory stress-tensor
with a special point-splitting regularization. Our computations go beyond the
approximation of the previous treatments and are valid at large coordinate
distances from the boundary at a finite time and up-to a finite coordinate
distance from the boundary at late time. In this region of validity our
regularization produces a certain singular term that is precisely canceled by
the collective field theory counter term in the present background. The energy
and momentum densities fall off exponentially at large distance from the
boundary to the values corresponding to the static background. This clearly
shows that the radiated energy reaches the asymptotic region signaling the
space-time decay.Comment: 37 pages, 5 figures. Section 6 is modified to clarify main
accomplishments of the paper including a discussion comparing stress-tensor
analysis with those preexisted in literature. Other modifications include
minor changes in the text and addition of one reference. Version accepted for
publication in JHE
Casimir Effect in 2D Stringy Black Hole Backgrounds
We consider the two-dimensional "Schwarzschild" and "Reissner-Nordstrom"
stringy black holes as systems of Casimir type. We explicitly calculate the
energy-momentum tensor of a massless scalar field satisfying Dirichlet boundary
conditions on two one-dimensional "walls". These results are obtained using the
Wald's axioms. Thermodynamical quantities such as pressure, specific heat,
isothermal compressibility and entropy of the two-dimensional stringy black
holes are calculated. A comparison is made between the obtained results and the
laws of thermodynamics. The results obtained for the extremal (Q=M) stringy
two-dimensional charged black hole are identical in all three different vacua
used; a fact that indicates its quantum stability.Comment: RevTeX, 27 pages, no figures, to appear in Phys.Rev. D, Vol 64 (Dec.
2001
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