Does Current Data Prefer a Non-minimally Coupled Inflaton?

Understand

We examine the impact of a non-minimal coupling of the inflaton to the Ricci scalar, $\frac12 \xi R\phi^2$, on the inflationary predictions.

• Such a non-minimal coupling is expected to be present in the inflaton Lagrangian on fairly general grounds.
• As a case study, we focus on the simplest inflationary model governed by the potential $V\propto \phi^2$, using the latest combined 2015 analysis of Planck and BICEP2/Keck Array.
• We find that the presence of a coupling $\xi$ is favoured at a significance of $99\%$ CL, assuming that nature has chosen the potential $V\propto \phi^2$ to generate the primordial perturbations and a number of e-foldings $N=60$.