Spinodal effect in the natural inflation model - art. no. 043505

Recently, Cormier and Holman pointed out that fluctuations of an inflaton f ield phi are significantly enhanced in the model of spinodal inflation with a potential V(phi) for which the second derivative V-(2)(phi) changes sign . As an application of this model, we investigate particle production in th e natural inflation model with a potential V(phi)=m(4)[1 + cos(phi/f)] by m aking use of the Hartree approximation. For typical mass scales f similar t o m(pl)similar to 10(19) GeV and m similar to m(GUT)similar to 10(16) GeV, we find that the growth of fluctuations relevantly occurs for the initial v alue of inflaton phi(0)less than or similar to 0.1m(pl). Especially for phi (0)less than or similar to 10(-6)m(pl), maximum fluctuations are so large t hat secondary inflation takes place by produced fluctuations. In this case, the achieved number of c-foldings becomes much larger than in the case whe re an effect of spinodal instability is neglected.