Resurrecting Quadratic Inflation with a non-minimal coupling to gravity

Abstract

We study Quadratic Inflation with the inflaton field ϕ coupled non-minimally to the curvature scalar R, so that the potential during inflation is of the form V∝ m2ϕ2+ξ Rϕ2. We show that with a suitable choice of the non-minimal coupling strength, ξ=\U0001d4aa(10−3), one can resurrect the success of the scenario when compared against the Planck and BICEP2/Keck Array data, and that in the region of the parameter space which is still allowed the model predicts values of the tensor-to-scalar ratio in the range 0.01⩽ r < 0.12, making it possible to either confirm the scenario or rule it out already by the current or near-future experiments, such as BICEP3 or LiteBIRD. However, we show that in this case the near-future observations are unlikely to be able to distinguish between the metric and Palatini formulations of gravity.