Inflation in supergravity from field redefinitions

Abstract

Supergravity (SUGRA) theories are specified by a few functions, most notably the real Kähler function denoted by $G(T_i, \bar {T}_i) = K + \log |W|^2$, where K is a real Kähler potential, and W is a holomorphic superpotential. A field redefinition $T_i \rightarrow f_1(T_i)$ does not change neither the theory, nor the Kähler geometry. Similarly, the Kähler transformation, $K \rightarrow K + f_2 + \bar f_2, W \rightarrow e^{-f_2} W$ where $f_2$ is holomorphic also leaves G and hence the theory and the geometry invariant. However, if we perform a field redefinition only in $K(T_i,\bar{T}_i) \rightarrow K(f(T_i),f(\bar{T}_i))$, while keeping the same superpotential $W(T_i)$, we get a different theory, as G is not invariant under such a transformation while maintaining the same Kähler geometry. This freedom of choosing $f(T_i)$ allows constructing an infinite number of new theories given a fixed Kähler geometry and a predetermined superpotential W. Our construction generalizes previous ones that were limited by the holomorphic property of $W$. In particular it allows for novel inflationary SUGRA models and particle phenomenology model building, where the different models correspond to different choices of field redefinitions. We demonstrate this possibility by constructing several prototypes of inflationary models (hilltop, Starobinsky-like, plateau, log-squared and bell-curve) all in flat Kähler geometry and an originally renormalizable superpotential $W$. The models are in accord with current observations and predict $r\in[10^{-6},0.06]$ spanning several decades that can be easily obtained. In the bell-curve model, there also exists a built-in gravitational reheating mechanism with $T_R\sim \mathcal{O}( 10^7 GeV)$.