5,320 research outputs found
Islands in the landscape
The string theory landscape consists of many metastable de Sitter vacua,
populated by eternal inflation. Tunneling between these vacua gives rise to a
dynamical system, which asymptotically settles down to an equilibrium state. We
investigate the effects of sinks to anti-de Sitter space, and show how their
existence can change probabilities in the landscape. Sinks can disturb the
thermal occupation numbers that would otherwise exist in the landscape and may
cause regions that were previously in thermal contact to be divided into
separate, thermally isolated islands.Comment: 31 pages, 8 figure
Towards a gauge invariant volume-weighted probability measure for eternal inflation
An improved volume-weighted probability measure for eternal inflation is
proposed. For the models studied in this paper it leads to simple and
intuitively expected gauge-invariant results.Comment: 16 pages, 3 figs, few misprints corrected, comments adde
Creation of the universe with a stealth scalar field
The stealth scalar field is a non-trivial configuration without any
back-reaction to geometry, which is characteristic for non-minimally coupled
scalar fields. Studying the creation probability of the de Sitter universe with
a stealth scalar field by the Hartle and Hawking's semi-classical method, we
show that the effect of the stealth field can be significant. For the class of
scalar fields we consider, creation with a stealth field is possible for a
discrete value of the coupling constant and its creation probability is always
less than that with a trivial scalar field. However, those creation rates can
be almost the same depending on the parameters of the theory.Comment: 7 pages; v2, references added; v3, creation of the open universe
adde
Reheating after Inflation
The theory of reheating of the Universe after inflation is developed. The
transition from inflation to the hot Universe turns out to be strongly
model-dependent and typically consists of several stages. Immediately after
inflation the field begins rapidly rolling towards the minimum of its
effective potential. Contrary to some earlier expectations, particle production
during this stage does not lead to the appearance of an extra friction term
in the equation of motion of the field . Reheating
becomes efficient only at the next stage, when the field rapidly
oscillates near the minimum of its effective potential. We have found that
typically in the beginning of this stage the classical inflaton field
very rapidly (explosively) decays into -particles or into other bosons
due to broad parametric resonance. This stage cannot be described by the
standard elementary approach to reheating based on perturbation theory. The
bosons produced at this stage, as well as some part of the classical field
which survives the stage of explosive reheating, should further decay
into other particles, which eventually become thermalized. The last stages of
decay can be described in terms of perturbation theory. Complete reheating is
possible only in those theories where a single massive -particle can
decay into other particles. This imposes strong constraints on the structure of
inflationary models. On the other hand, this means that a scalar field can be a
cold dark matter candidate even if it is strongly coupled to other fields.Comment: 7 pages, 1 figure, LaTeX, UH-IfA-94/35; SU-ITP-94-13; YITP/U-94-15
(paper replaced by its version to be published in Phys. Rev. Lett.
Inflation without Slow Roll
We draw attention to the possibility that inflation (i.e. accelerated
expansion) might continue after the end of slow roll, during a period of fast
oscillations of the inflaton field \phi . This phenomenon takes place when a
mild non-convexity inequality is satisfied by the potential V(\phi). The
presence of such a period of \phi-oscillation-driven inflation can
substantially modify reheating scenarios.
In some models the effect of these fast oscillations might be imprinted on
the primordial perturbation spectrum at cosmological scales.Comment: 9 pages, Revtex, psfig, 1 figure, minor modifications, references
adde
Jordan Frame Supergravity and Inflation in NMSSM
We present a complete explicit N=1, d=4 supergravity action in an arbitrary
Jordan frame with non-minimal scalar-curvature coupling of the form . The action is derived by suitably gauge-fixing the superconformal
action. The theory has a modified Kaehler geometry, and it exhibits a
significant dependence on the frame function and its
derivatives over scalars, in the bosonic as well as in the fermionic part of
the action. Under certain simple conditions, the scalar kinetic terms in the
Jordan frame have a canonical form. We consider an embedding of the
Next-to-Minimal Supersymmetric Standard Model (NMSSM) gauge theory into
supergravity, clarifying the Higgs inflation model recently proposed by Einhorn
and Jones. We find that the conditions for canonical kinetic terms are
satisfied for the NMSSM scalars in the Jordan frame, which leads to a simple
action. However, we find that the gauge singlet field experiences a strong
tachyonic instability during inflation in this model. Thus, a modification of
the model is required to support the Higgs-type inflation.Comment: 1+36 pages, 4 figures; v2: discussion updated in Subsec. 4.1, Refs.
added, typos fixed. To appear in PR
Resonance enhancement of particle production during reheating
We found a consistent equation of reheating after inflation, which shows that
for small quantum fluctuations the frequencies of resonance are slighted
different from the standard ones. Quantum interference is taken into account
and we found that at large fluctuations the process mimics very well the usual
parametric resonance but proceed in a different dynamical way. The analysis is
made in a toy quantum mechanical model and we discuss further its extension to
quantum field theory.Comment: 4 pages, 4 figures(eps), using RevTe
Can the Gravitational Wave Background from Inflation be Detected Locally?
The Cosmic Background Explorer (COBE) detection of microwave background
anisotropies may contain a component due to gravitational waves generated by
inflation. It is shown that the gravitational waves from inflation might be
seen using `beam-in-space' detectors, but not the Laser Interferometer Gravity
Wave Observatory (LIGO). The central conclusion, dependent only on weak
assumptions regarding the physics of inflation, is a surprising one. The larger
the component of the COBE signal due to gravitational waves, the {\em smaller}
the expected local gravitational wave signal.Comment: 8 pages, standard LaTeX (no figures), SUSSEX-AST 93/7-
Racetrack Inflation
We develop a model of eternal topological inflation using a racetrack
potential within the context of type IIB string theory with KKLT volume
stabilization. The inflaton field is the imaginary part of the K\"ahler
structure modulus, which is an axion-like field in the 4D effective field
theory. This model does not require moving branes, and in this sense it is
simpler than other models of string theory inflation. Contrary to
single-exponential models, the structure of the potential in this example
allows for the existence of saddle points between two degenerate local minima
for which the slow-roll conditions can be satisfied in a particular range of
parameter space. We conjecture that this type of inflation should be present in
more general realizations of the modular landscape. We also consider
`irrational' models having a dense set of minima, and discuss their possible
relevance for the cosmological constant problem.Comment: 23 pages 7 figures. The final version with minor modifications, to
appear in JHE
More on Tachyon Cosmology in De Sitter Gravity
We aim to study rolling tachyon cosmological solutions in de Sitter gravity.
The solutions are taken to be flat FRW type and these are not time-reversal
symmetric. We find that cosmological constant of our universe has to be
fine-tuned at the level of the action itself, as in KKLT string
compactification. The rolling tachyon can give rise to required inflation with
suitable choice of the initial conditions which include nonvanishing Hubble
constant. We also determine an upper bound on the volume of the
compactification manifold.Comment: 15pp, 3 figures; references adde
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