Minimal $R+R^2$ Supergravity Models of Inflation Coupled to Matter

TL;DR

This paper explores matter couplings in minimal supergravity models of inflation, revealing that matter must have an R-symmetry and that the inflaton potential arises from a D-term, with the vacuum always supersymmetric and metastable.

Contribution

It demonstrates how matter coupling in new minimal supergravity models requires R-symmetry and analyzes the resulting inflationary potential and vacuum structure.

Findings

Matter must possess an R-symmetry in these models.

Inflaton potential is generated by a D-term of the gauged R-symmetry.

The vacuum is always exactly supersymmetric and metastable.

Abstract

The supersymmetric extension of "Starobinsky" $R+\alpha R^2$ models of inflation is particularly simple in the "new minimal" formalism of supergravity, where the inflaton has no scalar superpartners. This paper is devoted to matter couplings in such supergravity models. We show how in the new minimal formalism matter coupling presents certain features absent in other formalisms. In particular, for the large class of matter couplings considered in this paper, matter must possess an R-symmetry, which is gauged by the vector field which becomes dynamical in the "new minimal" completion of the $R+\alpha R^2$ theory. Thus, in the dual formulation of the theory, where the gauge vector is part of a massive vector multiplet, the inflaton is the superpartner of the massive vector of a nonlinearly realized R-symmetry. The F-term potential of this theory is of no-scale type, while the inflaton potential is given by the D-term of the gauged R-symmetry. The absolute minimum of the potential is always exactly supersymmetric, so in this class of models if realistic vacua exist, they must be always metastable. We also briefly comment on possible generalizations of the examples discussed here and we exhibit some features of higher-curvature supergravity coupled to matter in the "old minimal" formalism.