Jordan Frame in Supergravity and Cosmology

Abstract

The superconformal action can be gauge-fixed in a gauge where is leads to the Einstein frame supergravity defined by a Kahler potential $K(z, \bar z)$, or in a gauge where it leads to a Jordan frame supergravity defined by the frame function $Ω(z, \bar z)$, in addition to $K(z, \bar z)$. We present new supergravity $ξ$-attractor models with non-minimal gravity coupling. They describe potentials with an exponential and a polynomial approach to the plateau. The previously known $ξ$-attractors in the large $ξ$ limit predicted the spectral index $n_{s} = 1-2/N$ and the tensor-to-scalar ratio $r\to {12\over N^2}$. The new $ξ$-attractors in the large $ξ$ limit predict $n_{s} \geq 1-2/N$ and $r\to 0$, which provides a better match to the recent observational data and makes these models a target for the future B-mode experiments with small $r$. New $ξ$-attractors have some features similar to those of Palatini attractors. However, we show that the Palatini gravity with nonminimal scalar coupling and an independent affine connection has no supergravity embedding.