Within the effective field theory of inflation , an initialization of the classical dynamics of the inflaton with approximate equipartition between the kinetic and potential energy of the inflaton leads to a brief fast roll stage that precedes the slow roll regime .
The fast roll stage leads to an attractive potential in the wave equations for the mode functions of curvature and tensor perturbations .
The evolution of the inflationary perturbations is equivalent to the scattering by this potential and a useful dictionary between the scattering data and observables is established .
Implementing methods from scattering theory we prove that this attractive potential leads to a suppression of the quadrupole moment for CMB and B-mode angular power spectra .
The scale of the potential is determined by the Hubble parameter during slow roll .
Within the effective field theory of inflation at the grand unification ( GUT ) energy scale we find that if inflation lasts a total number of efolds N _ { tot } \sim 59 , there is a 10 - 20 \% suppression of the CMB quadrupole and about 2 - 4 \% suppression of the tensor quadrupole .
The suppression of higher multipoles is smaller , falling off as 1 / l ^ { 2 } .
The suppression is much smaller for N _ { tot } > 59 , therefore if the observable suppression originates in the fast roll stage , there is the upper bound N _ { tot } \sim 59 .