Observational constraints on inflation with the nonlinear sigma fields in light of Plank 2015

TL;DR

This paper investigates an inflation model involving nonlinear sigma fields with SO(3) symmetry, deriving observable predictions and constraining the model using Planck 2015 data.

Contribution

It introduces a novel inflation model with nonlinear sigma fields maintaining homogeneity and isotropy, and provides observational constraints based on Planck 2015 data.

Findings

Constraints on model parameters from Planck 2015 data

Predictions for scalar and tensor power spectra

Implications for spectral indices and tensor-to-scalar ratio

Abstract

We study an inflation model with a nonlinear sigma field which has $SO(3)$ symmetry. The background solution of the nonlinear sigma field is proportional to the space coordinates linearly while keeping the homogeneous and isotropic background spacetime. We calculate the observable quantities including the power spectra of the scalar and tensor modes, the spectral indices, the tensor-to-scalar ratio, and the running of the spectral indices, and then constrain our model with the Planck 2015 observational data.