13,938 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
Entropy production and curvature perturbation from dissipative curvatons
Considering the curvaton field that follows dissipative slow-roll equation,
we show that the field can lead to entropy production and generation of
curvature perturbation after reheating. Spectral index is calculated to
discriminate warm and thermal scenarios of dissipative curvatons from the
standard curvaton model. In contrast to the original curvaton model, quadratic
potential is not needed in the dissipative scenario, since the growth in the
oscillating period is not essential for the model.Comment: 29 pages, 2 figures, accepted for publication in JCA
Hybrid Curvatons from Broken Symmetry
We present a new general mechanism for generating curvature perturbations
after inflation. Our model is based on the simple assumption that a field that
starts to oscillate after inflation has a potential characterized by an
underlying global symmetry that is slightly or badly broken. Inhomogeneous
preheating occurs due to the oscillation with the broken symmetry. Unlike the
traditional curvaton model, we will not identify the curvaton with the
oscillating field. The curvaton is identified with the preheat field that could
be either a scalar, vector, or fermionic field. We introduce an explicit mass
term for the curvaton, which is important for later evolution and the decay.
Our present model represents the simplest example of the hybrid of the
curvatons and inhomogeneous preheating.Comment: 21pages, 5 figures, accepted for publication in JHE
Cosmological perturbations from inhomogeneous preheating and multi-field trapping
We consider inhomogeneous preheating in a multi-field trapping model. The
curvature perturbation is generated by inhomogeneous preheating which induces
multi-field trapping at the enhanced symmetric point (ESP), and results in
fluctuation in the number of e-foldings. Instead of considering simple
reheating after preheating, we consider a scenario of shoulder inflation
induced by the trapping. The fluctuation in the number of e-foldings is
generated during this weak inflationary period, when the additional light
scalar field is trapped at the local maximum of its potential. The situation
may look similar to locked or thermal inflation or even to hybrid inflation,
but we will show that the present mechanism of generating the curvature
perturbation is very different from these others. Unlike the conventional
trapped inflationary scenario, we do not make the assumption that an ESP
appears at some unstable point on the inflaton potential. This assumption is
crucial in the original scenario, but it is not important in the multi-field
model. We also discuss inhomogeneous preheating at late-time oscillation, in
which the magnitude of the curvature fluctuation can be enhanced to accommodate
low inflationary scale.Comment: 18pages, 2 figures, to appear in JHE
Large N Expansion and Softly Broken Supersymmetry
We examine the supersymmetric non-linear O(N) sigma model with a soft
breaking term. In two dimensions, we found that the mass difference between
supersymmetric partner fields vanishes accidentally. In three dimensions, the
mass difference is observed but O(N) symmetry is always broken also in the
strong coupling region.Comment: Plain Latex(8pages), No Figur
Evolution of the curvature perturbations during warm inflation
This paper considers warm inflation as an interesting application of
multi-field inflation. Delta-N formalism is used for the calculation of the
evolution of the curvature perturbations during warm inflation. Although the
perturbations considered in this paper are decaying after the horizon exit, the
corrections to the curvature perturbations sourced by these perturbations can
remain and dominate the curvature perturbations at large scales. In addition to
the typical evolution of the curvature perturbations, inhomogeneous diffusion
rate is considered for warm inflation, which may lead to significant
non-Gaussianity of the spectrum.Comment: 23 pages, 1 figure, fixed references, accepted for publication in
JCA
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
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
Phase diagrams of a classical two-dimensional Heisenberg antiferromagnet with single-ion anisotropy
A classical variant of the two-dimensional anisotropic Heisenberg model
reproducing inelastic neutron scattering experiments on La_5 Ca_9 Cu_24 O_41
[M. Matsuda et al., Phys.Rev. B 68, 060406(R) (2003)] is analysed using mostly
Monte Carlo techniques. Phase diagrams with external fields parallel and
perpendicular to the easy axis of the anisotropic interactions are determined,
including antiferromagnetic and spin-flop phases. Mobile spinless defects, or
holes, are found to form stripes which bunch, debunch and break up at a phase
transition. A parallel field can lead to a spin-flop phase.Comment: 9 pages, 9 figures; final version as accepted by Phys. Rev. B (Fig. 5
replaced, added remarks in Secs. I, III, and V
Tadpole Method and Supersymmetric O(N) Sigma Model
We examine the phase structures of the supersymmetric O(N) sigma model in two
and three dimensions by using the tadpole method. Using this simple method, the
calculation is largely simplified and the characteristics of this theory become
clear. We also examine the problem of the fictitious negative energy state.Comment: Plain Latex(12pages), No figur
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