Particle decay during inflation: self-decay of inflaton quantum   fluctuations during slow roll
  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}. 
D. Boyanovsky, H. J. de Vega, N. G. Sanchez