  Natural inflation driven by Pseudo-Nambu-Goldstone bosons have a problem that
the nearly scale invariant spectrum of density perturbations is attained only
when the symmetry breaking scale is of the order of Planck scale. We show here
that if one couples the PNGB to a thermal bath as in warm inflation models, the
amplitude and spectral index which agrees with the WMAP data is obtained with
the symmetry breaking in the GUT scale. We give a GUT model of PNGB arising out
of spontaneously broken lepton number at the GUT scale which gives rise to
heavy Majorana masses for the right handed neutrinos which is needed in see-saw
models. This model also generates a lepton asymmetry because of the derivative
coupling of the PNGB to the lepton current. A characteristic feature of this
model is the prediction of large non-gaussianity which may be observed in the
forthcoming PLANCK experiment.
