258 research outputs found
Stable Exact Solutions in Cosmological Models with Two Scalar Fields
The stability of isotropic cosmological solutions for two-field models in the
Bianchi I metric is considered. We prove that the sufficient conditions for the
Lyapunov stability in the Friedmann-Robertson-Walker metric provide the
stability with respect to anisotropic perturbations in the Bianchi I metric and
with respect to the cold dark matter energy density fluctuations. Sufficient
conditions for the Lyapunov stability of the isotropic fixed points of the
system of the Einstein equations have been found. We use the superpotential
method to construct stable kink-type solutions and obtain sufficient conditions
on the superpotential for the Lyapunov stability of the corresponding exact
solutions. We analyze the stability of isotropic kink-type solutions for string
field theory inspired cosmological models.Comment: 23 pages, v3:typos corrected, references adde
On Nonlocal Modified Gravity and Cosmology
Despite many nice properties and numerous achievements, general relativity is
not a complete theory. One of actual approaches towards more complete theory of
gravity is its nonlocal modification. We present here a brief review of
nonlocal gravity with its cosmological solutions. In particular, we pay special
attention to two nonlocal models and their nonsingular bounce solutions for the
cosmic scale factor.Comment: 11 pages, Published in Springer Proceedings in Mathematics &
Statistics 111 (2014) 251-26
Localization of the SFT inspired Nonlocal Linear Models and Exact Solutions
A general class of gravitational models driven by a nonlocal scalar field
with a linear or quadratic potential is considered. We study the action with an
arbitrary analytic function , which has both simple and double roots.
The way of localization of nonlocal Einstein equations is generalized on models
with linear potentials. Exact solutions in the Friedmann-Robertson-Walker and
Bianchi I metrics are presented.Comment: 20 pages, 3 figures, published in the proceedings of the VIII
International Workshop "Supersymmetries and Quantum Symmetries" (SQS'09),
Dubna, Russia, July 29 - August 3, 2009, http://theor.jinr.ru/~sqs09
Brane-Induced Gravity's Shocks
We construct exact gravitational field solutions for a relativistic particle
localized on a tensional brane in brane-induced gravity. They are a
generalization of gravitational shock waves in 4D de Sitter space. We provide
the metrics for both the normal branch and the self-inflating branch DGP
braneworlds, and compare them to the 4D Einstein gravity solution and to the
case when gravity resides only in the 5D bulk, without any brane-localized
curvature terms. At short distances the wave profile looks the same as in four
dimensions. The corrections appear only far from the source, where they differ
from the long distance corrections in 4D de Sitter space. We also discover a
new non-perturbative channel for energy emission into the bulk from the
self-inflating branch, when gravity is modified at the de Sitter radius.Comment: 4 pages, revtex4; v4: a sign error corrected; the correction
tantamount to swapping normal and self-inflating branch solutions; the only
significant change is that the spectacular new instability is on the
self-inflating branch in the limit of vanishing brane tension; more details
available in hep-th/050203
On Gauge Equivalence of Tachyon Solutions in Cubic Neveu-Schwarz String Field Theory
Simple analytic solution to cubic Neveu-Schwarz String Field Theory including
the sector is presented. This solution is an analog of the
Erler-Schnabl solution for bosonic case and one of the authors solution for the
pure case. Gauge transformations of the new solution to others known
solutions for the string tachyon condensation are constructed explicitly.
This gauge equivalence manifestly supports the early observed fact that these
solutions have the same value of the action density.Comment: 8 pages, LaTe
Zeta Nonlocal Scalar Fields
We consider some nonlocal and nonpolynomial scalar field models originated
from p-adic string theory. Infinite number of spacetime derivatives is
determined by the operator valued Riemann zeta function through d'Alembertian
in its argument. Construction of the corresponding Lagrangians L starts
with the exact Lagrangian for effective field of p-adic tachyon
string, which is generalized replacing p by arbitrary natural number n and then
taken a sum of over all n. The corresponding new objects we
call zeta scalar strings. Some basic classical field properties of these fields
are obtained and presented in this paper. In particular, some solutions of the
equations of motion and their tachyon spectra are studied. Field theory with
Riemann zeta function dynamics is interesting in its own right as well.Comment: 13 pages, submitted to Theoretical and Mathematical Physic
Tachyon dark energy models: dynamics and constraints
We explore the dynamics of dark energy models based on a Dirac-Born-Infeld
(DBI) tachyonic action, studying a range of potentials. We numerically
investigate the existence of tracking behaviour and determine the present-day
value of the equation of state parameter and its running, which are compared
with observational bounds. We find that tachyon models have quite similar
phenomenology to canonical quintessence models. While some potentials can be
selected amongst many possibilities and fine-tuned to give viable scenarios,
there is no apparent advantage in choosing a DBI scalar field instead of a
Klein-Gordon one.Comment: 10 pages, 4 figures. v2: references added, matches the published
versio
FRW Cosmology with Non-positively Defined Higgs Potentials
We discuss the classical aspects of dynamics of scalar models with
non-positive Higgs potentials in the FRW cosmology. These models appear as
effective local models in non-local models related with string field theories.
After a suitable field redefinition these models have the form of local Higgs
models with a negative extra cosmological term and the total Higgs potential is
non-positively defined and has rather small coupling constant. The
non-positivity of the potential leads to the fact that on some stage of
evolution the expansion mode gives place to the mode of contraction, due to
that the stage of reheating is absent. In these models the hard regime of
inflation gives place to inflation near the hill top and the area of the slow
roll inflation is very small. Meanwhile one can obtain enough e-foldings before
the contraction to make the model under consideration admissible to describe
inflation.Comment: 40 pages, 20 figures, typos correcte
Nonlocal Dynamics of p-Adic Strings
We consider the construction of Lagrangians that might be suitable for
describing the entire -adic sector of an adelic open scalar string. These
Lagrangians are constructed using the Lagrangian for -adic strings with an
arbitrary prime number . They contain space-time nonlocality because of the
d'Alembertian in argument of the Riemann zeta function. We present a brief
review and some new results.Comment: 8 page
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
- …