  We consider a model of DBI inflation where two stacks of mobile branes are
moving ultra relativistically in a warped throat. The stack closer to the tip
of the throat is annihilated with the background anti-branes while inflation
proceeds by the second stack. The effects of branes annihilation and particles
creation during DBI inflation on the curvature perturbations power spectrum and
the scalar spectral index are studied. We show that for super-horizon scales,
modes which are outside the sound horizon at the time of branes collision, the
spectral index has a shift to blue spectrum compared to the standard DBI
inflation. For small scales the power spectrum approaches to its background DBI
inflation value with the decaying superimposed oscillatory modulations.
