Hybrid natural inflation from non-Abelian discrete symmetry

A spontaneously broken global discrete symmetry may have pseudo Goldstone modes associated with the spontaneous breaking of the approximate continuous symmetry of the low dimension terms in the Lagrangian. These provide natural candidates for an inflaton that can generate slow-roll inflation. We show that. in the case of a non-Abelian discrete symmetry, the pseudo Goldstone modes readily couple to further scalar fields in a manner that the end of inflation is determined by these additional scalar fields, generating hybrid inflation. We give a simple parameterisation of the inflationary potential in this case, determine the inflationary parameters resulting, and show that phenomenological Successful inflation is possible while keeping the scale of symmetry breaking sub-Planckian. Unlike natural inflation the inflation scale can be very low. We construct two simple hybrid inflation models, one non-supersymmetric and one supersymmetric. In the latter case no parameters need be chosen anomalously small. (C) 2010 Elsevier B.V. All rights reserved.