No-Scale Inflation

TL;DR

No-scale supergravity, derived from string compactifications, offers a natural framework for inflation that aligns with observational data, predicting a tilted scalar spectrum and low tensor-to-scalar ratio.

Contribution

This paper demonstrates that no-scale supergravity models produce inflationary predictions similar to the Starobinsky model, linking string theory and cosmological observations.

Findings

Predicted scalar spectral index n_s ~ 0.96

Tensor-to-scalar ratio r < 0.1

Consistent with Planck CMB data

Abstract

Supersymmetry is the most natural framework for physics above the TeV scale, and the corresponding framework for early-Universe cosmology, including inflation, is supergravity. No-scale supergravity emerges from generic string compactifications and yields a non-negative potential, and is therefore a plausible framework for constructing models of inflation. No-scale inflation yields naturally predictions similar to those of the Starobinsky model based on $R + R^2$ gravity, with a tilted spectrum of scalar perturbations: $n_s \sim 0.96$, and small values of the tensor-to-scalar perturbation ratio $r < 0.1$, as favoured by Planck and other data on the cosmic microwave background (CMB). Detailed measurements of the CMB may provide insights into the embedding of inflation within string theory as well as its links to collider physics.