46 research outputs found
Resonant nucleation of spatio-temporal order via parametric modal amplification
We investigate, analytically and numerically, the emergence of
spatio-temporal order in nonequilibrium scalar field theories. The onset of
order is triggered by destabilizing interactions (DIs), which instantaneously
change the interacting potential from a single to a double-well, tunable to be
either degenerate (SDW) or nondegenerate (ADW). For the SDW case, we observe
the emergence of spatio-temporal coherent structures known as oscillons. We
show that this emergence is initially synchronized, the result of parametric
amplification of the relevant oscillon modes. We also discuss how these ordered
structures act as bottlenecks for equipartition. For ADW potentials, we show
how the same parametric amplification mechanism may trigger the rapid decay of
a metastable state. For a range of temperatures, the decay rates associated
with this resonant nucleation can be orders of magnitude larger than those
computed by homogeneous nucleation, with time-scales given by a simple power
law, , where depends weakly on the
temperature and is the free-energy barrier of a critical
fluctuation.Comment: 38 pages, 20 figures now included within the tex
A Note on Inflation with Tachyon Rolling on the Gauss-Bonnet Brane
In this paper we study the tachyonic inflation in brane world cosmology with
Gauss-Bonnet term in the bulk. We obtain the exact solution of slow roll
equations in case of exponential potential. We attempt to implement the
proposal of Lidsey and Nunes, astro-ph/0303168, for the tachyon condensate
rolling on the Gauss-Bonnet brane and discuss the difficulties associated with
the proposal.Comment: RevTex4, 5 pages, no figures, Minor clarifications added and
references updated, To appear in PR
Inflationary Attractor in Braneworld Scenario
We demonstrate the attractor behavior of inflation driven by a scalar field
or a tachyon field in the context of recently proposed four-dimensional
effective gravity induced on the world-volume of a three-brane in
five-dimensional Einstein gravity, and we obtain a set of exact inflationary
solutions. Phase portraits indicate that an initial kinetic term decays rapidly
and it does not prevent the onset of inflation. The trajectories more rapidly
reach the slow-roll curve than in the standard cosmology.Comment: 7 pages, 8 figures, RevTeX, to appear in Phys. Rev. D69 (2004
Non-minimally Coupled Tachyonic Inflation in Warped String Background
We show that the non-minimal coupling of tachyon field to the scalar
curvature, as proposed by Piao et al, with the chosen coupling parameter does
not produce the effective potential where the tachyon field can roll down from
T=0 to large along the slope of the potential. We find a correct choice of
the parameters which ensures this requirement and support slow-roll inflation.
However, we find that the cosmological parameter found from the analysis of the
theory are not in the range obtained from observations. We then invoke warped
compactification and varying dilaton field over the compact manifold, as
proposed by Raeymaekers, to show that in such a setup the observed parameter
space can be ensured.Comment: minor typos corrected and references adde
Electromagnetic String Fluid in Rolling Tachyon
We study Born-Infeld type effective action for unstable D3-brane system
including a tachyon and an Abelian gauge field, and find the rolling tachyon
with constant electric and magnetic fields as the most general homogeneous
solution. Tachyonic vacua are characterized by magnitudes of the electric and
magnetic fields and the angle between them. Analysis of small fluctuations in
this background shows that the obtained configuration may be interpreted as a
fluid consisting of string-like objects carrying electric and magnetic fields.
They are stretched along one direction and the rolling tachyon move in a
perpendicular direction to the strings. Direction of the propagating waves
coincides with that of strings with velocity equal to electric field.Comment: LaTeX, 18 pages, 1 figure, minor correction
D-brane anti-D-brane effective action and brane interaction in open string channel
We construct the effective action of a -brane-anti--brane system by
making use of the non-abelian extension of tachyonic DBI action. We succeed the
construction by restricting the Chan-Paton factors of two non-BPS -branes
in the action to the Chan-Paton factors of a system. For the
special case that both branes are coincident, the action reduces to the one
proposed by A. Sen. \\The effective potential indicates that
when branes separation is larger than the string length scale, there are two
minima in the tachyon direction. As branes move toward each other under the
gravitational force, the tachyon tunneling from false to true vacuum may make a
bubble formation followed by a classical evolution of the bubble. On the other
hand, when branes separation is smaller than the string length scale, the
potential shows one maximum and one minimum. In this case, a homogeneous
tachyon rolling in real time makes an attractive potential for the branes
distance. This classical force is speculated to be the effective force between
the two branes.Comment: Latex, 14 pages, 1 figure, the version appears in JHE
Inflationary Attractor from Tachyonic Matter
We study the complete evolution of a flat and homogeneous universe dominated
by tachyonic matter. We demonstrate the attractor behaviour of the tachyonic
inflation using the Hamilton-Jacobi formalism. We else obtain analytical
approximations to the trajectories of the tachyon field in different regions.
The numerical calculation shows that an initial non-vanishing momentum does not
prevent the onset of inflation. The slow-rolling solution is an attractor.Comment: 4 pages, 2 figures, RevTe
Off-shell extension of S-matrix elements and tachyonic effective actions
We show that the on-shell S-matrix elements of four open string massless
scalars, two scalars and two tachyons, and four open string tachyons in the
super string theory can be written in a unique form. We then propose an
off-shell extension for the S-matrix element of four scalars which is
consistent, in the low energy limit, with the Dirac-Born-Infeld effective
action. Using a similar off-shell extension for the S-matrix element of two
scalars and two tachyons and for the S-matrix element of four tachyons, we show
that they are fully consistent with the tachyonic DBI action.Comment: Latex, 17 pages, v3:a paragraph comparing off-shell and on- shell
amplitudes added, reference adde
Phantom with Born-Infield type Lagrangian
Recent analysis of the observation data indicates that the equation of state
of the dark energy might be smaller than -1, which leads to the introduction of
phantom models featured by its negative kinetic energy to account for the
regime of equation of state . In this paper, we generalize the idea to
the Born-Infield type Lagrangian with negative kinetic energy term and give the
condition for the potential, under which the late time attractor solution
exists and also analyze a viable cosmological model in such a scheme.Comment: 13 pages, 6 figures, Reference updated, the final version will be
published in Phys. Rev.
Cosmological Dynamics of Phantom Field
We study the general features of the dynamics of the phantom field in the
cosmological context. In the case of inverse coshyperbolic potential, we
demonstrate that the phantom field can successfully drive the observed current
accelerated expansion of the universe with the equation of state parameter
. The de-Sitter universe turns out to be the late time attractor
of the model. The main features of the dynamics are independent of the initial
conditions and the parameters of the model. The model fits the supernova data
very well, allowing for at 95 % confidence level.Comment: Typos corrected. Some clarifications and references added. To appear
in Physical Review