On FLRW reductions of N=1 supergravity

An FLRW reduction of N=1 supergravity is troublesome since spatial isotropy prohibits a non-vanishing Rarita-Schwinger field. In view of this, we consider the quadratic form $\psi_m^{\ \alpha} \psi_{n \alpha}$ arising from a particular superspace generalization of the metric tensor. Imposing the FLRW form on this object reduces $\psi_m^{\ \alpha}$ to a single 2-component spinor $\phi^\alpha$, which becomes the superpartner of both the scale factor $a$ and lapse $N$, thus inducing the conformal time gauge, $N=a$. Time-reparametrization invariance is restored if we allow for deviations of FLRW form that are proportional to the gauge fields $N, \psi_0^{\ \alpha}$. We determine the allowed supergravity transformations that preserve the resulting FLRW supermultiplets.