The return of Palatini inflationary attractors: Universal mapping of observables

Abstract

We study single-field slow-roll inflation in the context of Palatini gravity for the class of non-minimally coupled $\xi$-attractors, i.e.,\ models where the same function $f(\varphi )$ fixes both the non-minimal coupling, $1+\xi f(\varphi )$, and the inflationary potential, $V(\varphi )=V_{0}f(\varphi {)}^2$. As is well-known, for an arbitrary $f(\varphi )$, the number of $e$-folds is, at leading order, independent of $\xi$. Thanks to this, we provide an immediate mapping between the observables of the non-minimally coupled setup and those of the minimally coupled one. In the strong coupling limit, the tensor-to-scalar ratio is, as usual, suppressed, while the scalar spectral index is shifted towards larger values, with the magnitude of the shift depending only on the tensor-to-scalar ratio associated with the original potential $V(\varphi )$.

9 pages