Two-Field Analysis of No-Scale Supergravity Inflation

TL;DR

This paper extends the analysis of two-field supergravity inflation models, showing how effects in no-scale supergravity can significantly influence inflationary predictions for key observables like the spectral index and tensor-to-scalar ratio.

Contribution

It generalizes the two-field inflation analysis to arbitrary Kähler potentials in supergravity, revealing how two-field effects can modify inflationary predictions and reduce the tensor-to-scalar ratio.

Findings

Two-field effects can lower the tensor-to-scalar ratio $r$ to very small values.

The spectral index $n_s$ can interpolate between different inflationary models.

Non-Gaussianity $f_{NL}$ remains below current experimental sensitivity.

Abstract

Since the building-blocks of supersymmetric models include chiral superfields containing pairs of effective scalar fields, a two-field approach is particularly appropriate for models of inflation based on supergravity. In this paper, we generalize the two-field analysis of the inflationary power spectrum to supergravity models with arbitrary K\"ahler potential. We show how two-field effects in the context of no-scale supergravity can alter the model predictions for the scalar spectral index $n_s$ and the tensor-to-scalar ratio $r$, yielding results that interpolate between the Planck-friendly Starobinsky model and BICEP2-friendly predictions. In particular, we show that two-field effects in a chaotic no-scale inflation model with a quadratic potential are capable of reducing $r$ to very small values $\ll 0.1$. We also calculate the non-Gaussianity measure $f_{\rm NL}$, finding that is well below the current experimental sensitivity.