23 research outputs found
Chaotic Inflation on the Brane with Induced Gravity
We study the slow-roll inflationary dynamics in a self-gravitating induced
gravity braneworld model with bulk cosmological constant. For E \gg
M_{5}^{3}/M^{2}_{2} we find important corrections to the four-dimensional
Friedmann equation which bring the standard chaotic inflationary scenario in
closer agreement with recent observations. For \lambda/M^{3}_{5} \ll E \ll
M^{3}_{5}/M^{2}_{4} we find five-dimensional corrections to the Friedmann
equation, which give the known Randall-Sundrum results of the inflationary
parameters.Comment: LaTex file, 21 pages, 3 figures, the energy scales are redefined, new
results on the chaotic inflation, typos are corrected. Accepted for
publication in JCA
Bi-paracontact structures and Legendre foliations
We study almost bi-paracontact structures on contact manifolds. We prove that
if an almost bi-paracontact structure is defined on a contact manifold
, then under some natural assumptions of integrability, carries
two transverse bi-Legendrian structures. Conversely, if two transverse
bi-Legendrian structures are defined on a contact manifold, then admits an
almost bi-paracontact structure. We define a canonical connection on an almost
bi-paracontact manifold and we study its curvature properties, which resemble
those of the Obata connection of an anti-hypercomplex (or complex-product)
manifold. Further, we prove that any contact metric manifold whose Reeb vector
field belongs to the -nullity distribution canonically carries an
almost bi-paracontact structure and we apply the previous results to the theory
of contact metric -spaces.Comment: To appear on: Kodai Mathematical Journa
BTZ Solutions on Codimension-2 Braneworlds
We consider five-dimensional gravity with a Gauss-Bonnet term in the bulk and
an induced gravity term on a 2-brane of codimension-2. We show that this system
admits BTZ-like black holes on the 2-brane which are extended into the bulk
with regular horizons.Comment: 6 pages. Talk given at Recent Developments in Gravity (NEB XIII),
Thessaloniki, Greece, June 4-6, 2008
A late-accelerating universe with no dark energy - And a finite-temperature big bang
Brane-world models offer the possibility of explaining the late acceleration
of the universe via infra-red modifications to General Relativity, rather than
a dark energy field. However, one also expects ultra-violet modifications to
General Relativity, when high-energy stringy effects in the early universe
begin to grow. We generalize the DGP brane-world model via an ultra-violet
modification, in the form of a Gauss-Bonnet term in the bulk action. The
combination of infra-red and ultra-violet modifications produces an intriguing
cosmology. The DGP feature of late-time acceleration without dark energy is
preserved, but there is an entirely new feature - there is no hot big bang in
the early universe. The universe starts with finite density and pressure, from
a "sudden" curvature singularity.Comment: revised title and minor improvements, additional references; to
appear JCA
AdS/CFT Correspondence and the Reheating of the Brane-Universe
We present a mechanism for exit from inflation and reheating using the
AdS/CFT correspondence. A cosmological evolution is induced on a probe D3-brane
as it moves in a black D-brane background of type-0 string theory. If the
tachyon field is non zero, inflation is induced on the brane-universe, with the
equation of state parameter in the range -1<w<-1/3 depending on the position of
the probe brane in the bulk. As the probe brane approaches the horizon of the
background black hole, the inflation rate decreases and the value of w gets
larger. At some critical distance away from the horizon, inflation ends. When
the brane-universe reaches the horizon, the conformal invariance is restored,
the background geometry becomes AdS{5}X S{5}, and the brane-universe feels the
CFT thermal radiation and reheats.Comment: LaTex file, 18 pages, 2 figures, accepted for publication in JHE
Instability of brane cosmological solutions with flux compactifications
We discuss the stability of the higher-dimensional de Sitter (dS) brane
solutions with two-dimensional internal space in the Einstein-Maxwel theory. We
show that an instability appears in the scalar-type perturbations with respect
to the dS spacetime. We derive a differential relation which has the very
similar structure to the ordinary laws of thermodynamics as an extension of the
work for the six-dimensional model [20]. In this relation, the area of dS
horizon (integrated over the two internal dimensions) exactly behaves as the
thermodynamical entropy. The dynamically unstable solutions are in the
thermodynamically unstable branch. An unstable dS compactification either
evolves toward a stable configuration or two-dimensional internal space is
decompactified. These dS brane solutions are equivalent to the accelerating
cosmological solutions in the six-dimensional Einstein-Maxwell-dilaton theory
via dimensional reduction. Thus, if the seed higher-dimensional solution is
unstable, the corresponding six-dimensional solution is also unstable. From the
effective four-dimensional point of view, a cosmological evolution from an
unstable cosmological solution in higher dimensions may be seen as a process of
the transition from the initial cosmological inflation to the current dark
energy dominated Universe.Comment: 11 pages, 3 figures, references added, to appear in CQ
Inflation on a Warped Dvali-Gabadadze-Porrati Brane
We discuss an inflation model, in which the inflation is driven by a single
scalar field with exponential potential on a warped DGP brane. In contrast to
the power law inflation in standard model, we find that the inflationary phase
can exit spontaneously without any mechanism. The running of the index of
scalar perturbation spectrum can take an enough large value to match the
observation data, while other parameters are in a reasonable region.Comment: Revtex, v3: 15 pages including 6 eps figures, some changes made and
references added, to appear in JCA
Low energy effective theory on a regularized brane in 6D gauged chiral supergravity
We derive the low energy effective theory on a brane in six-dimensional
chiral supergravity. The conical 3-brane singularities are resolved by
introducing cylindrical codimension one 4-branes whose interiors are capped by
a regular spacetime. The effective theory is described by the Brans-Dicke (BD)
theory with the BD parameter given by . The BD field is
originated from a modulus which is associated with the scaling symmetry of the
system. If the dilaton potentials on the branes preserve the scaling symmetry,
the scalar field has an exponential potential in the Einstein frame. We show
that the time dependent solutions driven by the modulus in the four-dimensional
effective theory can be lifted up to the six-dimensional exact solutions found
in the literature. Based on the effective theory, we discuss a possible way to
stabilize the modulus to recover standard cosmology and also study the
implication for the cosmological constant problem.Comment: 12 pages, 1 figur
Hybrid compactifications and brane gravity in six dimensions
We consider a six-dimensional axisymmetric Einstein-Maxwell model of warped
braneworlds. The bulk is bounded by two branes, one of which is a conical
3-brane and the other is a 4-brane wrapped around the axis of symmetry. The
latter brane is assumed to be our universe. If the tension of the 3-brane is
fine-tuned, it folds the internal two-dimensional space in a narrow cone,
making sufficiently small the Kaluza-Klein circle of the 4-brane. An arbitrary
energy-momentum tensor can be accommodated on this ring-like 4-brane. We study
linear perturbations sourced by matter on the brane, and show that weak gravity
is apparently described by a four-dimensional scalar-tensor theory. The extra
scalar degree of freedom can be interpreted as the fluctuation of the internal
space volume (or that of the circumference of the ring), the effect of which
turns out to be suppressed at long distances. Consequently, four-dimensional
Einstein gravity is reproduced on the brane. We point out that as in the
Randall-Sundrum model, the brane bending mode is crucial for recovering the
four-dimensional tensor structure in this setup.Comment: 15 pages, 2 figures; v2: references added; v3: accepted for
publication in Class. Quant. Gra
Probing the Holography of Near-Horizon AdS(5)xS(5) Geometry
Using the AdS/CFT correspondence we study the holographic principle and the
CFT/FRW relations in the near-horizon AdS(5)xS(5) geometry with a probe
D3-brane playing the role of the boundary to this space. The motion of the
probe D3-brane in the bulk, induces a cosmological evolution on the brane. As
the brane crosses the horizon of the bulk black hole, it probes the holography
of the dual CFT. We test the holographic principle and we find corrections to
CFT/FRW relations in various physical cases: for radially moving, spinning and
electrically charged D3-brane and for a NS/NS B-field in the bulk.Comment: LaTex file, 30 pages, no figures; major revision, new results
presented, references added; to appear in JCA