Hybrid Inflation from Supergravity D Terms

TL;DR

This work proposes a D-term–driven hybrid inflation scenario in supergravity to solve the inflaton-mass problem characteristic of F-term inflation, by using an anomalous U(1) D-term to provide the vacuum energy. A two-field toy model with W = c σ φ^2 and K = -log(σ+σ̄) + φ φ̄ yields a slow-roll regime where the inflaton mass arises only at one loop, enabling $m^2_\sigma \ll H^2$ and successful inflation, followed by a hybrid exit when $\phi$ becomes tachyonic. The model can reproduce the observed density perturbations with plausible parameter choices ($M \sim M_P/300$, $c \sim 0.1$) and naturally arises in string-derived supergravity with anomalous U(1) factors. The authors argue that such D-term–driven scenarios are generic in certain string constructions (e.g., free-fermionic models) and could provide a concrete link between early-universe cosmology and string theory.

Abstract

We argue that the mass of the inflaton can be much smaller than the Hubble constant in supergravity models in which inflation is driven by D--terms and not F--terms. We investigate a supergravity toy model which leads to hybrid inflation due to an anomalous D--term. We show that the slow--roll condition can be satisfied and the correct magnitude for density perturbations can be obtained for some choice of model parameters. The kind of model considered can naturally arise in some string derived supergravity models.