Asko Jokinen

Non-Gaussianity from preheating

We consider a two-field model for inflation where the second order metric perturbations can be amplified by a parametric resonance during preheating. We demonstrate that there can arise a considerable enhancement of non-Gaussianity sourced by the local terms generated through the coupled perturbations. We argue that the non-Gaussianity parameter could be as large as f(NL) approximately 50. Our results may provide a useful test of preheating in future cosmic microwave background experiments.

Non-Gaussianity from instant and tachyonic preheating

We study non-Gaussianity in two distinct models of preheating: instant and tachyonic. In instant preheating non-Gaussianity is sourced by the local terms generated through the coupled perturbations of the two scalar fields. We find that the non-Gaussianity parameter is given by , where g is a coupling constant, so that instant preheating is unlikely to be constrained by WMAP or Planck. In the case of tachyonic preheating non-Gaussianity arises solely from the instability of the tachyon matter and is found to be large. We find that for single-field inflation the present WMAP data imply a bound on the scale of tachyonic instability. We argue that the tachyonic preheating limits are useful also for string-motivated inflationary models.

Seed perturbations for primordial magnetic fields from MSSM flat directions

We demonstrate that the MSSM flat directions can naturally account for the seed magnetic fields in the early Universe. The non-zero vacuum expectation value of an MSSM flat direction condensate provides masses to the gauge fields and thereby breaks conformal invariance. During inflation the condensate receives spatial perturbations and

Very large primordial non-gaussianity from multi-field: application to massless preheating

SU(2) x U(1)_Y

Minimal supersymmetric standard model flat direction as a curvaton

gauge currents are generated together with (hyper)magnetic fields. When these long wavelength vector perturbations reenter our horizon they give rise to

Inflation in large N limit of supersymmetric gauge theories

U(1)_{em}

Cosmological constraints on string scale and coupling arising from tachyonic instability

magnetic fields with an amplitude of

Flat direction condensate instabilities in the MSSM

10^{-30}

Identifying the curvaton within MSSM

Gauss, as required by the dynamo mechanism.We demonstrate that the minimally supersymmetric standard model (MSSM) flat directions can naturally account for the seed magnetic fields in the early Universe. The non-zero vacuum expectation value of an MSSM flat direction condensate provides masses to the gauge fields and thereby breaks conformal invariance. During inflation the condensate receives spatial perturbations and SU(2) × U(1)Y gauge currents are generated together with (hyper)magnetic fields. When these long wavelength vector perturbations re-enter our horizon they give rise to U(1)em magnetic fields with an amplitude of 10−30xa0G, as required by the dynamo mechanism.

Numerical simulations of fragmentation of the Affleck-Dine condensate

In this paper we derive a generic expression which is valid for scales larger than the Hubble radius and contains only local terms, for the second order curvature perturbations for more than one field, provided that the expansion is sourced from the energy density of a single field. As an application, motivated by our previous paper (Enqvist et al, 2005?Phys.?Rev.?Lett.?94?161301), we apply our formalism to two fields during preheating, where the inflaton oscillations are sourced from a ?4 potential which is governing the expansion of the Universe. A second field ?, coupled to the inflaton through g22?2, is excited from the vacuum fluctuations. The excited modes of ? amplify the super-Hubble isocurvature perturbations, which seed the second order curvature perturbations, giving rise to a significantly large non-Gaussianity. Our results show that within three inflaton oscillations for a range of parameters, 1?<?g2/??<?3, the non-Gaussianity parameter becomes , which is already ruled out by the current WMAP observation.