7,649 research outputs found
Inflation with
We discuss various models of inflationary universe with . A
homogeneous universe with may appear due to creation of the
universe "from nothing" in the theories where the effective potential becomes
very steep at large , or in the theories where the inflaton field
nonminimally couples to gravity. Inflation with generally requires
intermediate first order phase transition with the bubble formation, and with a
second stage of inflation inside the bubble. It is possible to realize this
scenario in the context of a theory of one scalar field, but typically it
requires artificially bent effective potentials and/or nonminimal kinetic
terms. It is much easier to obtain an open universe in the models involving two
scalar fields. However, these models have their own specific problems. We
propose three different models of this type which can describe an open
homogeneous inflationary universe.Comment: 29 pages, LaTeX, parameters of one of the models are slightly
modifie
Volume Weighted Measures of Eternal Inflation in the Bousso-Polchinski Landscape
We consider the cosmological dynamics associated with volume weighted
measures of eternal inflation, in the Bousso-Polchinski model of the string
theory landscape. We find that this measure predicts that observers are most
likely to find themselves in low energy vacua with one flux considerably larger
than the rest. Furthermore, it allows for a satisfactory anthropic explanation
of the cosmological constant problem by producing a smooth, and approximately
constant, distribution of potentially observable values of Lambda. The low
energy vacua selected by this measure are often short lived. If we require
anthropically acceptable vacua to have a minimum life-time of 10 billion years,
then for reasonable parameters a typical observer should expect their vacuum to
have a life-time of approximately 12 billion years. This prediction is model
dependent, but may point toward a solution to the coincidence problem of
cosmology.Comment: 35 pages, 8 figure
A symmetry for vanishing cosmological constant: Another realization
A more conventional realization of a symmetry which had been proposed towards
the solution of cosmological constant problem is considered. In this study the
multiplication of the coordinates by the imaginary number in the literature
is replaced by the multiplication of the metric tensor by minus one. This
realization of the symmetry as well forbids a bulk cosmological constant and
selects out dimensional spaces. On contrary to its previous
realization the symmetry, without any need for its extension, also forbids a
possible cosmological constant term which may arise from the extra dimensional
curvature scalar provided that the space is taken as the union of two
dimensional spaces where the usual 4-dimensional space lies at the intersection
of these spaces. It is shown that this symmetry may be realized through
spacetime reflections that change the sign of the volume element. A possible
relation of this symmetry to the E-parity symmetry of Linde is also pointed
out.Comment: The version to appear in PLB. The terms "non-orientable space" and
"extra-dimensional tranlation" are replaced by "space whose volume element
changes sign under extra dimensional reflections" and "extra dimensional
reflections", respectively; and typos are correcte
Stationarity of Inflation and Predictions of Quantum Cosmology
We describe several different regimes which are possible in inflationary
cosmology. The simplest one is inflation without self-reproduction of the
universe. In this scenario the universe is not stationary. The second regime,
which exists in a broad class of inflationary models, is eternal inflation with
the self-reproduction of inflationary domains. In this regime local properties
of domains with a given density and given values of fields do not depend on the
time when these domains were produced. The probability distribution to find a
domain with given properties in a self-reproducing universe may or may not be
stationary, depending on the choice of an inflationary model. We give examples
of models where each of these possibilities can be realized, and discuss some
implications of our results for quantum cosmology. In particular, we propose a
new mechanism which may help solving the cosmological constant problem.Comment: 30 pages, Stanford preprint SU-ITP-94-24, LaTe
The weight for random quark masses
In theories in which the parameters of the low energy theory are not unique,
perhaps having different values in different domains of the universe as is
possible in some inflationary models, the fermion masses would be distributed
with respect to some weight. In such a situation the specifics of the fermion
masses do not have a unique explanation, yet the weight provides the visible
remnant of the structure of the underlying theory. This paper introduces this
concept of a weight for the distribution of masses and provides a quantitative
estimate of it from the observed quarks and leptons. The weight favors light
quark masses and appears roughly scale invariant (rho ~ 1/m). Some relevant
issues, such as the running of the weight with scale and the possible effects
of anthropic constraints, are also discussed.Comment: 35pages, 19 figure
STATIONARY SOLUTIONS IN BRANS-DICKE STOCHASTIC INFLATIONARY COSMOLOGY
In Brans-Dicke theory the Universe becomes divided after inflation into many
exponentially large domains with different values of the effective
gravitational constant. Such a process can be described by diffusion equations
for the probability of finding a certain value of the inflaton and dilaton
fields in a physical volume of the Universe. For a typical chaotic inflation
potential, the solutions for the probability distribution never become
stationary but grow forever towards larger values of the fields. We show here
that a non-minimal conformal coupling of the inflaton to the curvature scalar,
as well as radiative corrections to the effective potential, may provide a
dynamical cutoff and generate stationary solutions. We also analyze the
possibility of large nonperturbative jumps of the fluctuating inflaton scalar
field, which was recently revealed in the context of the Einstein theory. We
find that in the Brans--Dicke theory the amplitude of such jumps is strongly
suppressed.Comment: 19 pages, LaTe
Quantum Creation of an Open Inflationary Universe
We discuss a dramatic difference between the description of the quantum
creation of an open universe using the Hartle-Hawking wave function and the
tunneling wave function. Recently Hawking and Turok have found that the
Hartle-Hawking wave function leads to a universe with Omega = 0.01, which is
much smaller that the observed value of Omega > 0.3. Galaxies in such a
universe would be about light years away from each other, so the
universe would be practically structureless. We will argue that the
Hartle-Hawking wave function does not describe the probability of the universe
creation. If one uses the tunneling wave function for the description of
creation of the universe, then in most inflationary models the universe should
have Omega = 1, which agrees with the standard expectation that inflation makes
the universe flat. The same result can be obtained in the theory of a
self-reproducing inflationary universe, independently of the issue of initial
conditions. However, there exist two classes of models where Omega may take any
value, from Omega > 1 to Omega << 1.Comment: 23 pages, 4 figures. New materials are added. In particular, we show
that boundary terms do not help to solve the problem of unacceptably small
Omega in the new model proposed by Hawking and Turok in hep-th/9803156. A
possibility to solve the cosmological constant problem in this model using
the tunneling wave function is discusse
Decoherence, instantons, and cosmological horizons
We consider the possibility that tunneling in a degenerate double-well
potential in de Sitter spacetime leads to coherent oscillations of quantum
probability to find the system in a given well. We concentrate on the case when
the mass scale of the potential is much larger than the Hubble parameter and
present a procedure for analytical continuation of the ``time''-dependent
instantons, which allows us to study the subsequent real-time evolution. We
find that the presence of the de Sitter horizon makes tunneling completely
incoherent and calculate the decoherence time. We discuss the difference
between this case and the case of a -vacuum, when tunneling in de
Sitter spacetime preserves quantum coherence.Comment: 21 pages, latex, 3 figure
Some Cosmological Implications of Hidden Sectors
We discuss some cosmological implications of extensions of the Standard Model
with hidden sector scalars coupled to the Higgs boson. We put special emphasis
on the conformal case, in which the electroweak symmetry is broken radiatively
with a Higgs mass above the experimental limit. Our refined analysis of the
electroweak phase transition in this kind of models strengthens the prediction
of a strongly first-order phase transition as required by electroweak
baryogenesis. We further study gravitational wave production and the
possibility of low-scale inflation as well as a viable dark matter candidate.Comment: 23 pages, 8 figures; some comments added, published versio
GUT Phase Transition and Hybrid Inflation
The supersymmetric model of hybrid inflation is interesting not only because
of its naturalness but also because of another reason. Its energy scale
determined by the COBE normalization is 10^15 - 10^16 GeV. It happens to be the
energy scale of interest in particle physics, namely, the mass scale of
right-handed neutrinos or the energy scale of the gauge-coupling unification.
It is true that topological defects are produced after the hybrid inflation if
it is related to a U(1)_B-L or a GUT-symmetry breaking, and hence one cannot
naively identify models of particle physics with that of inflation. But those
defects are not necessarily found in modified models. We show in this article
that quite a simple extension of the minimal supersymmetric hybrid inflation
model is free from monopoles or cosmic strings. Moreover, it happens to be
exactly the same as a well-motivated extension of SU(5)-unified theories. The
vacuum energy is dominated by F-term. The \eta-problem is not necessarily
serious when the model is realized by D-branes. Although it has been considered
that a coupling constant has to be very small when the vacuum energy is
dominated by F-term, this constraint is not applied either to the D-brane
model. They are due to a particular form of the Kahler potential and
interaction of the model. Reheating process is also discussed.Comment: 11 pages; references adde
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