Helical phase inflation and its observational constraints

We consider a class of helical phase inflation models from the ${\mathcal N}=1$ supergravity where the phase component of a complex field acts as an inflaton. This class of models avoids the eta problem in supergravity inflation due to the phase monodromy of the superpotential. We study the inflationary predictions of this class of models in the context of both standard and large extra dimensional brane cosmology, and find that they can easily accommodate the Planck 2018 and BICEP2 constraints. We find that the helical phase inflation has $\alpha$-attractors and the attractors depend on one model parameter only.