Pre-inflationary relics in the CMB?

String Theory and Supergravity allow, in principle, to follow the transition of the inflaton from pre-inflationary fast roll to slow roll. This introduces an infrared depression in the primordial power spectrum that might have left an imprint in the CMB anisotropy, if it occurred at accessible wavelengths. We model the effect extending ΛCDM with a scale ΔΔ related to the infrared depression and explore the constraints allowed by Planck 2015 data, employing also more conservative, wider Galactic masks in the low resolution CMB likelihood. In an extended mask with fsky=39%fsky=39%, we thus find Δ=(0.351±0.114)×10−3Mpc−1, at 99.4% confidence level, to be compared with a nearby value at 88.5% with the standard fsky=94%fsky=94% mask. With about 64 ee-folds of inflation, these values for ΔΔ would translate into primordial energy scales O(1014)GeV.