Lower tensor to scalar ratio in a SUGRA motivated inflationary potential

TL;DR

This paper explores a supergravity-inspired inflationary potential that yields a very low tensor-to-scalar ratio, consistent with Planck 2018 data, and examines reheating constraints related to SUSY breaking scales.

Contribution

It introduces a D-term dominated supergravity inflationary potential with slow roll features leading to a low tensor-to-scalar ratio and analyzes reheating bounds within this framework.

Findings

Achieves a tensor-to-scalar ratio of order 10^{-3}.

Predicts inflationary observables within Planck 2018 1-sigma bounds.

Identifies parameter space for reheating temperature consistent with gravitino constraints.

Abstract

A scalar potential obtained from the $D$-term in the Supergravity models, which dominates over $F$ term and is mainly responsible for the inflationary phase in the early universe, is studied. The potential with canonical kinetic terms for scalar fields in the Lagrangian, has a very slow roll feature in comparison to various other plateau type inflationary potentials. In this case, a much lower tensor-to-scalar ratio ($r$) of $\mathcal{O}(10^{-3})$ is achievable. The requirement of slow roll condition for the inflation potential implies that the up type neutral scalar and the down type neutral scalar in Supergravity models are with equal field strength at the time of inflation. If this relationship holds down to the electroweak scale for the corresponding $vev$ values of these fields, then it will indicate a higher SUSY breaking scale around 100 TeV. The predicted values of the inflationary observables are well within the 1-$\sigma$ bounds of the recent constraints from {\it Planck'18} observations. The era of reheating after the inflationary phase, is also studied and the bounds on the reheating temperature ($T_{re}$) is calculated for a different equation of states during reheating ($w_{re}$) for the {\it Planck'18} allowed values of the scalar spectral index ($n_s$). For our model with $w_{re}=2/3$ and $w_{re}=1$, after satisfying all the bounds due to gravitino overproduction, we can have big parameter space for $T_{re}$ which is well inside {\it Planck'18} 1-$\sigma$ bound on $n_s$.