1,327 research outputs found
A thermodynamical model for non-extremal black p-brane
We show that the correct entropy, temperature (and absorption probability) of
non-extremal black p-brane can be reproduced by a certain thermodynamical model
when maximizing its entropy. We show that the form of the model is related to
the geometrical similarity of non-extremal and near extremal black p-brane at
near horizon region, and argue about the appropriateness of the model.Comment: Almost the same version as the paper appeared in Physical Review
Microscopic Entropy of Non-dilatonic Branes: a 2D approach
We investigate non-dilatonic p-branes in the near-extremal, near-horizon
regime. A two-dimensional gravity model, obtained from dimensional reduction,
gives an effective description of the brane. We show that the AdS_p+2/CFT_p+1
correspondence at finite temperature admits an effective description in terms
of a AdS_2/CFT_1 duality endowed with a scalar field, which breaks the
conformal symmetry and generates a non-vanishing central charge. The entropy of
the CFT_1 is computed using Cardy formula. Fixing in a natural way a free,
dimensionless, parameter introduced in the model by a renormalization
procedure, we find exact agreement between the CFT_1 entropy and the
Bekenstein-Hawking entropy of the brane.Comment: 10 pages, no figure
Antibranes don't go black
When D-branes are inserted in flux backgrounds of opposite charge, the
resulting solution has a certain singularity in the fluxes. Recently it has
been argued, using numerical solutions, that for anti-D3 branes in the
Klebanov-Strassler background these singularities cannot be cloaked by a
horizon, which strongly suggests they are not physical. In this note we provide
an analytic proof that the singularity of all codimension-three antibrane
solutions (such as anti-D6 branes in massive type IIA supergravity or anti-D3
branes smeared on the T^3 of R^3xT^3 with fluxes) cannot be hidden behind a
horizon, and that the charge of black branes with smooth event horizons must
have the same sign as the charge of the flux background. Our result indicates
that infinitesimally blackening the antibranes immediately triggers brane-flux
annihilation, and strengthens the intuition that antibranes placed in flux with
positive charge immediately annihilate against it.Comment: 9 pages, 1 figur
Universal dS vacua in STU-models
Stable de Sitter solutions in minimal F-term supergravity are known to lie
close to Minkowski critical points. We consider a class of STU-models arising
from type IIB compactifications with generalised fluxes. There, we apply an
analytical method for solving the equations of motion for the moduli fields
based on the idea of treating derivatives of the superpotential of different
orders up to third as independent objects. In particular, supersymmetric and
no-scale Minkowski solutions are singled out by physical reasons. Focusing on
the study of dS vacua close to supersymmetric Minkowski points, we are able to
elaborate a complete analytical treatment of the mass matrix based on the
sGoldstino bound. This leads to a class of interesting universal dS vacua. We
finally explore a similar possibility around no-scale Minkowski points and
discuss some examples.Comment: 31 pages, 4 figures and 7 table
Transplanckian energy production and slow roll inflation
In this paper we investigate how the energy density due to a non-standard
choice of initial vacuum affects the expansion of the universe during
inflation. To do this we introduce source terms in the Friedmann equations
making sure that we respect the relation between gravity and thermodynamics. We
find that the energy production automatically implies a slow rolling
cosmological constant. Hence we also conclude that there is no well defined
value for the cosmological constant in the presence of sources. We speculate
that a non-standard vacuum can provide slow roll inflation on its own.Comment: 16 pages, 2 figures, version 2: minor corrections to section 4 and
references adde
Mimicking transPlanckian effects in the CMB with conventional physics
We investigate the possibility that fields coupled to the inflaton can
influence the primordial spectrum of density perturbations through their
coherent motion. For example, the second field in hybrid inflation might be
oscillating at the beginning of inflation rather than at the minimum of its
potential. Although this effect is washed out if inflation lasts long enough,
we note that there can be up to 30 e-foldings of inflation prior to horizon
crossing of COBE fluctuations while still giving a potentially visible
distortion. Such pumping of the inflaton fluctuations by purely conventional
physics can resemble transPlanckian effects which have been widely discussed.
The distortions which they make to the CMB could leave a distinctive signature
which differs from generic effects like tilting of the spectrum.Comment: 3 pages, 4 figures; presented at PASCOS 03, TIFR, Mumbai, Indi
10 + 1 to 3 + 1 in an Early Universe with mutually BPS Intersecting Branes
We assume that the early universe is homogeneous, anisotropic, and is
dominated by the mutually BPS 22'55' intersecting branes of M theory. The
spatial directions are all taken to be toroidal. Using analytical and numerical
methods, we study the evolution of such an universe. We find that,
asymptotically, three spatial directions expand to infinity and the remaining
spatial directions reach stabilised values. Any stabilised values can be
obtained by a fine tuning of initial brane densities. We give a physical
description of the stabilisation mechanism. Also, from the perspective of four
dimensional spacetime, the effective four dimensional Newton's constant G_4 is
now time varying. Its time dependence will follow from explicit solutions. We
find in the present case that, asymptotically, G_4 exhibits characteristic log
periodic oscillations.Comment: Latex file, 59 pages, 7 figures. Version 2: A minor correction and a
reference added. Version 3: Critical discussion of the main assumptions is
added in sections I and VIII; two references added. To appear in Physical
Review
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