We examine the impact of a non-minimal coupling of the inflaton to the Ricci scalar , \frac { 1 } { 2 } \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 .
Within the context of the same scenario , we find that the value of \xi is different from zero at the 2 \sigma level .
When considering the cross-correlation polarization spectra from BICEP2/ Keck Array and Planck , a value of r = 0.038 _ { -0.030 } ^ { +0.039 } is predicted in this particular non-minimally coupled scenario .
Future cosmological observations may therefore test these values of r and verify or falsify the non-minimally coupled model explored here .