We obtain the effective inflaton potential during slow roll inflation by
including the one loop quantum corrections to the energy momentum tensor from
scalar curvature and tensor perturbations as well as quantum fluctuations from
light scalars and light Dirac fermions generically coupled to the inflaton.
During slow roll inflation there is a clean and unambiguous separation between
superhorizon and subhorizon contributions to the energy momentum tensor. The
superhorizon part is determined by the curvature perturbations and scalar field
fluctuations: both feature infrared enhancements as the inverse of a
combination of slow roll parameters which measure the departure from scale
invariance in each case.Fermions and gravitons do not exhibit infrared
divergences. The subhorizon part is completely specified by the trace anomaly
of the fields with different spins and is solely determined by the space-time
geometry. The one-loop quantum corrections to the amplitude of curvature and
tensor perturbations are obtained to leading order in slow-roll and in the
(H/M_PL)^2 expansion. This study provides a complete assessment of the
backreaction problem up to one loop including bosonic and fermionic degrees of
freedom. The result validates the effective field theory description of
inflation and confirms the robustness of the inflationary paradigm to quantum
fluctuations. Quantum corrections to the power spectra are expressed in terms
of the CMB observables:n_s, r and dn_s/dln k. Trace anomalies (especially the
graviton part) dominate these quantum corrections in a definite direction: they
enhance the scalar curvature fluctuations and reduce the tensor fluctuations.Comment: 18 pages, no figure