9,631 research outputs found
Aspects of warm-flat directions
Considering the mechanism of dissipative slow-roll that has been used in warm
inflation scenario, we show that dissipation may alter usual cosmological
scenarios associated with SUSY-flat directions. We mainly consider SUSY-flat
directions that have strong interactions with non-flat directions and may cause
strong dissipation both in thermal and non-thermal backgrounds. An example is
the Affleck-Dine mechanism in which dissipation may create significant (both
qualitative and quantitative) discrepancies between the conventional scenario
and the dissipative one. We also discuss several mechanisms of generating
curvature perturbations in which the dissipative field, which is distinguished
from the inflaton field, can be used as the source of cosmological
perturbations. Considering the Morikawa-Sasaki dissipative coefficient, the
damping caused by the dissipation may be significant for many MSSM flat
directions even if the dissipation is far from thermal equilibrium.Comment: 22 pages, accepted for publication in International Journal of Modern
Physics
Brane inflation without slow-roll
The scenario of brane inflation without using the conventional slow-roll
approximations has been investigated. Based on the mechanism of generating the
curvature perturbations at the end of inflation, a new brane inflation paradigm
was developed. The conditions for making a sufficiently large enough number of
e-foldings and for generating the curvature perturbations without producing
dangerous relics were also examined. Benefits of our scenario are subsequently
discussed in detail.Comment: 21 pages, 2 figures, added an appendix, accepted for publication in
JHE
Curvaton paradigm can accommodate multiple low inflation scales
Recent arguments show that some curvaton field may generate the cosmological
curvature perturbation. As the curvaton is independent of the inflaton field,
there is a hope that the fine-tunings of inflation models can be cured by the
curvaton scenario. More recently, however, D.H.Lyth discussed that there is a
strong bound for the Hubble parameter during inflation even if one assumes the
curvaton scenario. Although the most serious constraint was evaded, the bound
seems rather crucial for many models of a low inflation scale. In this paper we
try to remove this constraint. We show that the bound is drastically modified
if there were multiple stages of inflation.Comment: 9pages, no figure, references added, final versio
Generating the curvature perturbation with instant preheating
A new mechanism for generating the curvature perturbation at the end of
inflaton has been investigated. The dominant contribution to the primordial
curvature perturbation may be generated during the period of instant
preheating. The mechanism converts isocurvature perturbation related to a light
field into curvature perturbation, where the ``light field'' is not the
inflaton field. This mechanism is important in inflationary models where
kinetic energy is significant at the end of inflaton. We show how one can apply
this mechanism to various brane inflationary models.Comment: 17 pages, 1 figure, To appear in JCA
Elliptic Inflation: Generating the curvature perturbation without slow-roll
There are many inflationary models in which inflaton field does not satisfy
the slow-roll condition. However, in such models, it is always difficult to
generate the curvature perturbation during inflation. Thus, to generate the
curvature perturbation, one must introduce another component to the theory. To
cite a case, curvatons may generate dominant part of the curvature perturbation
after inflation. However, we have a question whether it is unrealistic to
consider the generation of the curvature perturbation during inflation without
slow-roll. Assuming multi-field inflation, we encounter the generation of the
curvature perturbation during inflation without slow-roll. The potential along
equipotential surface is flat by definition and thus we do not have to worry
about symmetry. We also discuss about KKLT models, in which corrections lifting
the inflationary direction may not become a serious problem if there is a
symmetry enhancement at the tip (not at the moving brane) of the inflationary
throat.Comment: 27pages, 8figures, to appear in JCA
Dark matter production from cosmic necklaces
Cosmic strings have gained a great interest, since they are formed in a large
class of brane inflationary models. The most interesting story is that cosmic
strings in brane models are distinguished in future cosmological observations.
If the strings in brane models are branes or superstrings that can move along
compactified space, and also if there are degenerated vacua along the
compactified space, kinks interpolate between degenerated vacua become
``beads'' on the strings. In this case, strings turn into necklaces. In the
case that the compact manifold in not simply connected, a string loop that
winds around a nontrivial circle is stable due to the topological reason. Since
the existence of the (quasi-)degenerated vacua and the nontrivial circle is a
common feature of the brane models, it is important to study cosmological
constraints on the cosmic necklaces and the stable winding states. In this
paper, we consider dark matter production from loops of the cosmic necklaces.
Our result suggests that necklaces can put stringent bound on certain kinds of
brane models.Comment: 27 pages, 5 figures, added many comments and 3 figures, accepted for
publication in JCA
Evolution of curvature perturbation in generalized gravity theories
Using the cosmological perturbation theory in terms of the delta-N formalism,
we find the simple formulation of the evolution of the curvature perturbation
in generalized gravity theories. Compared with the standard gravity theory, a
crucial difference appears in the end-boundary of the inflationary stage, which
is due to the non-ideal form of the energy momentum tensor that depends
explicitly on the curvature scalar. Recent study shows that
ultraviolet-complete quantum theory of gravity may be approximated by using a
generalized gravity action. Our paper may give an important step in
understanding the evolution of the curvature perturbation during inflation,
where the energy momentum tensor may not be given by the ideal form due to the
corrections from the fundamental theory.Comment: 15pages, fixed references, accepted for publication in CQ
How Can We Obtain a Large Majorana-Mass in Calabi-Yau Models ?
In a certain type of Calabi-Yau superstring models it is clarified that the
symmetry breaking occurs by stages at two large intermediate energy scales and
that two large intermediate scales induce large Majorana-masses of right-handed
neutrinos. Peculiar structure of the effective nonrenormalizable interactions
is crucial in the models. In this scheme Majorana-masses possibly amount to
O(10^{9 \sim 10}\gev) and see-saw mechanism is at work for neutrinos. Based
on this scheme we propose a viable model which explains the smallness of masses
for three kind of neutrinos .
Special forms of the nonrenormalizable interactions can be understood as a
consequence of an appropriate discrete symmetry of the compactified manifold.Comment: 30-pages + 6-figures, LaTeX, Preprint DPNU-94-02, AUE-01-9
- âŠ