The power spectrum of the cosmic microwave background from both the Planck and WMAP data exhibits a slight dip for multipoles in the range of l = 10 - 30 .
We show that such a dip could be the result of the resonant creation of massive particles that couple to the inflaton field .
For our best-fit models , the epoch of resonant particle creation reenters the horizon at a wave number of k _ { * } \sim 0.00011 \pm 0.0004 ( h 
Mpc ^ { -1 } ) .
The amplitude and location of this feature corresponds to the creation of a number of degenerate fermion species of mass \sim ( 8 - 11 ) / \lambda ^ { 3 / 2 } m _ { pl } during inflation where \lambda \sim ( 1.0 \pm 0.5 ) N ^ { -2 / 5 } is the coupling constant between the inflaton field and the created fermion species , while N is the number of degenerate species .
Although the evidence is of marginal statistical significance , this could constitute new observational hints of unexplored physics beyond the Planck scale .