  Particle decay during inflation is studied by implementing a dynamical
renormalization group resummation combined with a small Delta expansion. Delta
measures the deviation from the scale invariant power spectrum and regulates
the infrared. In slow roll inflation, Delta is a simple function of the slow
roll parameters epsilon_V, eta_V.We find that quantum fluctuations can
self-decay as a consequence of the inflationary expansion through processes
which are forbidden in Minkowski space-time. We compute the self-decay of the
inflaton quantum fluctuations during slow roll inflation.For wavelengths deep
inside the Hubble radius the decay is enhanced by the emission of ultrasoft
collinear quanta, i.e. bremsstrahlung radiation of superhorizon quanta which
becomes the leading decay channel for physical wavelengths
H<<k_{ph}(eta)<<H/(eta_V-eps_V). The decay of short wavelength fluctuations
hastens as the physical wave vector approaches the horizon. Superhorizon
fluctuations decay with a power law eta^Gamma in conformal time where in terms
of the amplitude of curvature perturbations Delta^2_R, the scalar spectral
index n_s, the tensor to scalar ratio r and slow roll parameters: Gamma \simeq
[32 xi^2_V Delta^2_R]/ /(n_s-1+r/4)^2.The behavior of the growing mode
eta^{eta_V-epsilon_V+Gamma}/eta features an anomalous scaling dimension Gamma.
We discuss the implications of these results for scalar and tensor
perturbations and for non-gaussianities in the power spectrum. The recent WMAP
data suggests Gamma >3.6 10^{-9}.
