Symmetry Breaking Indication for Supergravity Inflation in Light of the Planck 2015

TL;DR

This paper investigates how explicit symmetry breaking in supergravity inflation models can reconcile theoretical predictions with Planck 2015 data, predicting observable tensor fluctuations and spectral indices.

Contribution

It introduces symmetry breaking terms in supergravity inflation models to improve their compatibility with observational data, especially regarding tensor fluctuations.

Findings

Symmetry breaking leads to modulated inflaton potentials compatible with Planck data.

Models predict tensor-to-scalar ratios around 0.01, testable in future observations.

Breaking terms of order 10^{-2} significantly enhance inflation predictions.

Abstract

The supergravity (SUGRA) theories with exact global $U(1)$ symmetry or shift symmetry in K\"ahler potential provide the natural frameworks for inflation. However, the quadratic inflation is disfavoured by the new results on primordial tensor fluctuations from the Planck Collaboration. To be consistent with the new Planck data, we point out that the explicit symmetry breaking is needed, and study these two SUGRA inflation in details. For the SUGRA inflation with global $U(1)$ symmetry, the symmetry breaking term leads to a trigonometric modulation on inflaton potential. The coefficient of the $U(1)$ symmetry breaking term is of the order $10^{-2}$, which is sufficient large to improve the inflationary predictions while its higher order corrections are negligible. Such models predict sizeable tensor fluctuations and highly agree with the Planck results. In particular, the model with a linear $U(1)$ symmetry breaking term predicts the tensor-to-scalar ratio around $\textbf{r}\sim0.01$ and running spectral index $\alpha_s\sim-0.004$, which comfortably fit with the Planck observations. For the SUGRA inflation with breaking shift symmetry, the inflaton potential is modulated by an exponential factor. The modulated linear and quadratic models are consistent with the Planck observations. In both kinds of models the tensor-to-scalar ratio can be of the order $10^{-2}$, which will be tested by the near future observations.