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 \ll k _ { ph } ( \eta ) \ll H / ( \eta _ { V } - \epsilon _ { 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 \triangle ^ { 2 } _ { \mathcal { R } } , the scalar spectral index n _ { s } , the tensor to scalar ratio r and slow roll parameters :

\Gamma \simeq \frac { 32 \xi ^ { 2 } _ { V } \triangle ^ { 2 } _ { \mathcal { R } } } { ( n _ { s } -1 + \frac% { r } { 4 } ) ^ { 2 } } \left [ 1 + \mathcal { O } ( \epsilon _ { V } , \eta _ { V } ) \right ] . 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 as well as for non-gaussianities in the power spectrum .
The recent WMAP data suggests \Gamma \gtrsim 3.6 \times 10 ^ { -9 } .