Chaotic hybrid new inflation in supergravity with a running spectral index

TL;DR

The paper tackles the challenge of realizing a running spectral index within a supergravity framework. It proposes a sequential inflation scenario—chaotic inflation realized via a shift-symmetric inflaton, followed by hybrid inflation that generates $n_s>1$ on large scales and $n_s<1$ on smaller scales, and finally a dynamically initiated new inflation—to set up observable cosmological scales with the desired spectrum. By introducing spurion fields and a carefully designed superpotential $W=W_H+W_I+W_N$, the model achieves natural couplings, a controlled initial condition for new inflation, and a consistent amplitude ${\cal R}$ for density perturbations, while keeping a single underlying energy scale determined by the spurions. The analysis yields viable parameter choices, including a gravitino mass around tens of TeV, and demonstrates how early star formation and reionization can be accommodated within this unified supergravity construction.

Abstract

We propose an inflation model in supergravity, in which chaotic and hybrid inflation occurs successively, followed by new inflation. During hybrid inflation, adiabatic fluctuations with a running spectral index with $\ns >1$ on a large scale and $\ns <1$ on a smaller scale are generated, as favored by recent results of the first year Wilkinson Microwave Anisotropy Probe. The initial condition of new inflation is also set dynamically during hybrid inflation, and its duration and the amplitude of density fluctuations take appropriate values to help early star formation to realize early reionization.