Preheating can convert superhorizon fluctuations of light scalar fields present at the end of inflation into observable density perturbations. We show in detail how lattice field theory simulations and the separate universes approximation can be used to calculate these perturbations and make predictions for the nonlinearity parameter f NL . We also present a simple approximation scheme that can reproduce these results analytically. Applying these methods to the massless preheating model, we determine the parameter values that are ruled out by too high levels of non-Gaussianity.PACS numbers: 98.80.Cq, 11.15.Kc NL < 111, −151 < f equil. NL < 253 at 95% confidence limit. However, a recent work [8] using the WMAP three-year data found a significant non-Gaussianity: 26.9 < f local NL < 146.7 at 95% confidence limit. Measurements of large scale structure give
Our simulation code, which was used to produce the numerical results in Fig. 1 and Table 1, contained an error. The lattice discretization of the expression (8) for the energy density was incorrect, and the calculated quantity was therefore not the conserved energy that corresponds to the discretized lattice field equations. As a consequence, the numerical results cannot be trusted. This does not affect the validity of the method we described in our Letter. Corrected simulation results will appear in Ref. [1]. We thank the authors of that paper for pointing out this error to us.[1] J.
We calculate curvature perturbations in the scenario in which the curvaton field decays into another scalar field via parametric resonance. As a result of a nonlinear stage at the end of the resonance, standard perturbative calculation techniques fail in this case. Instead, we use lattice field theory simulations and the separate universe approximation to calculate the curvature perturbation as a nonlinear function of the curvaton field. For the parameters tested, the generated perturbations are highly non-Gaussian and not well approximated by the usual f NL parameterisation. Resonant decay plays an important role in the curvaton scenario and can have a substantial effect on the resulting perturbations.
If light scalar fields are present at the end of inflation, their nonequilibrium dynamics such as parametric resonance or a phase transition can produce non-Gaussian density perturbations. We show how these perturbations can be calculated using nonlinear lattice field theory simulations and the separate universe approximation. In the massless preheating model, we find that some parameter values are excluded while others lead to acceptable but observable levels of non-Gaussianity. This shows that preheating can be an important factor in assessing the viability of inflationary models.
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