64 research outputs found
Cosmological Aspects of Rolling Tachyon
We examine the possibility of rolling tachyon to play the dual roll of
inflaton at early epochs and dark matter at late times. We argue that enough
inflation can be generated with the rolling tachyon either by invoking the
large number of branes or brane world assisted inflation. However, reheating is
problematic in this model.Comment: RevTeX 4 pages, Talk delivered in PASCOS held at TIFR (Mumbai) from
3rd Jan to 9th Jan. To appear in the proceedings of PASCOS to be published in
a special issue of Praman
Quintessential inflation
We present an explicit observationally acceptable model for evolution from
inflation to the present epoch under the assumption that the entropy and matter
of the familiar universe are from gravitational particle production at the end
of inflation. This eliminates the problem of finding a satisfactory coupling of
the inflaton and matter fields. Since the inflaton potential may be a
monotonic function of the inflaton , the inflaton energy could produce an
observationally significant effective cosmological constant, as in
quintessence.Comment: 6 pages, REVTeX, 1 figur
Phase Transition in Conformally Induced Gravity with Torsion
We have considered the quantum behavior of a conformally induced gravity in
the minimal Riemann-Cartan space. The regularized one-loop effective potential
considering the quantum fluctuations of the dilaton and the torsion fields in
the Coleman-Weinberg sector gives a sensible phase transition for an
inflationary phase in De Sitter space. For this effective potential, we have
analyzed the semi-classical equation of motion of the dilaton field in the
slow-rolling regime.Comment: 7pages, no figur
Some exact non-vacuum Bianchi VI0 and VII0 instantons
We report some new exact instantons in general relativity. These solutions
are K\"ahler and fall into the symmetry classes of Bianchi types VI0 and VII0,
with matter content of a stiff fluid. The qualitative behaviour of the
solutions is presented, and we compare it to the known results of the
corresponding self-dual Bianchi solutions. We also give axisymmetric Bianchi
VII0 solutions with an electromagnetic field.Comment: latex, 15 pages with 3 eps figure
Curvaton reheating: an application to braneworld inflation
The curvaton was introduced recently as a distinct inflationary mechanism for
generating adiabatic density perturbations. Implicit in that scenario is that
the curvaton offers a new mechanism for reheating after inflation, as it is a
form of energy density not diluted by the inflationary expansion. We consider
curvaton reheating in the context of a braneworld inflation model, {\em steep
inflation}, which features a novel use of the braneworld to give a new
mechanism for ending inflation. The original steep inflation model featured
reheating by gravitational particle production, but the inefficiency of that
process brings observational difficulties. We demonstrate here that the
phenomenology of steep inflation is much improved by curvaton reheating.Comment: 8 pages RevTeX4 file with two figures incorporated. Improved
referencing, matches PRD accepted versio
How long before the end of inflation were observable perturbations produced?
We reconsider the issue of the number of e-foldings before the end of
inflation at which observable perturbations were generated. We determine a
plausible upper limit on that number for the standard cosmology which is around
60, with the expectation that the actual value will be up to 10 below this. We
also note a special property of the model which reduces the
uncertainties in that case and favours a higher value, giving a fairly definite
prediction of 64 e-foldings for that model. We note an extreme (and highly
implausible) situation where the number of e-foldings can be even higher,
possibly up to 100, and discuss the shortcomings of quantifying inflation by
e-foldings rather than by the change in . Finally, we discuss the impact of
non-standard evolution between the end of inflation and the present, showing
that again the expected number of e-foldings can be modified, and in some cases
significantly increased.Comment: 7 pages RevTeX4 file with one figure incorporated. Minor updates to
match version accepted by Physical Review
Aspects of Tachyonic Inflation with Exponential Potential
We consider issues related to tachyonic inflation with exponential potential.
We find exact solution of evolution equations in the slow roll limit in FRW
cosmology. We also carry out similar analysis in case of Brane assisted
tachyonic inflation. We investigate the phase space behavior of the system and
show that the dust like solution is a late time attractor. The difficulties
associated with reheating in the tachyonic model are also indicated.Comment: New References added. To appear in Phys. Rev.
Relic Gravity Waves from Braneworld Inflation
We discuss a scenario in which extra dimensional effects allow a scalar field
with a steep potential to play the dual role of the inflaton as well as dark
energy (quintessence). The post-inflationary evolution of the universe in this
scenario is generically characterised by a `kinetic regime' during which the
kinetic energy of the scalar field greatly exceeds its potential energy
resulting in a `stiff' equation of state for scalar field matter . The kinetic regime precedes the radiation dominated epoch and
introduces an important new feature into the spectrum of relic gravity waves
created quantum mechanically during inflation. The gravity wave spectrum
increases with wavenumber for wavelengths shorter than the comoving horizon
scale at the commencement of the radiative regime. This `blue tilt' is a
generic feature of models with steep potentials and imposes strong constraints
on a class of inflationary braneworld models. Prospects for detection of the
gravity wave background by terrestrial and space-borne gravity wave
observatories such as LIGO II and LISA are discussed.Comment: Revised in response to referee's suggestions. Main conclusions
strengthened. 23 pages latex, 9 figures. Accepted for publication in Phys.
Rev.
Gravitino Production After Inflation
We investigate the production of gravitinos in a cosmological background.
Gravitinos can be produced during preheating after inflation due to a combined
effect of interactions with an oscillating inflaton field and absence of
conformal invariance. In order to get insight on conformal properties of
gravitino we reformulate phenomenological supergravity in SU(2,2|1)-symmetric
way. The Planck mass and F- and D-terms appear via the gauge-fixed value of a
superfield that we call conformon. We find that in general the probability of
gravitino production is not suppressed by the small gravitational coupling.
This may lead to a copious production of gravitinos after inflation. Efficiency
of the new non-thermal mechanism of gravitino production is very sensitive to
the choice of the underlying theory. This may put strong constraints on certain
classes of inflationary models.Comment: 18 pages, v2: the version to be published in Phys. Rev.D; v3:
matching notations with longer paper hep-th/000617
Dynamics of Scalar field in a Brane World
We study the dynamics of a scalar field in the brane cosmology. We assume
that a scalar field is confined in our 4-dimensional world. As for the
potential of the scalar field, we discuss three typical models: (1) a power-law
potential, (2) an inverse-power-law potential, and (3) an exponential
potential. We show that the behavior of the scalar field is very different from
a conventional cosmology when the energy density square term is dominated.Comment: 15pages, 8figures, submitted to Physical Review
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