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

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

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

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

On gaugino condensation in the effective theory

We analyze the gaugino condensation in the effective theory for N=1 SU(N) Supersymmetric QCD with $N_{f}$ flavors. It is known that taking the vacuum expectation value of the matter field to be infinite, we can show that gaugino condensation can occur. At such a limit we should consider only pure supersymmetric Yang-Mills theory. But when we include an interaction term of order $O(\frac{1}{v})$, the situation can change. We analyze the effect of this interaction term and examine the gaugino condensation in the low energy Yang-Mills theory by using the scheme of Nambu-Jona-Lasinio.Comment: 5 pages, Plain Late

Q ball inflation

We show that inflation can occur in the core of a Q-ball.Comment: 11 pages, latex2e, no figure, references added, final version to appear in PR

String production after angled brane inflation

We describe string production after angled brane inflation. First, we point out that there was a discrepancy in previous discussions. The expected tension of the cosmic string calculated from the four-dimensional effective Lagrangian did not match the one obtained in the brane analysis. In the previous analysis, the cosmic string is assumed to correspond to the lower-dimensional daughter brane, which wraps the same compactified space as the original mother brane. In this case, however, the tension of the daughter brane cannot depend on the angle (\theta). On the other hand, from the analysis of the effective Lagrangian for tachyon condensation, it is easy to see that the tension of the cosmic string must be proportional to \theta, when \theta << 1. This is an obvious discrepancy that must be explained by consideration of the explicit brane dynamics. In this paper, we will solve this problem by introducing a simple idea. We calculate the tension of the string in the two cases, which matches precisely. The cosmological constraint for angled inflation is relaxed, because the expected tension of the cosmic string becomes smaller than the one obtained in previous arguments, by a factor of \theta.Comment: 13pages, 3 figures, typos correcte

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

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