Multiple inflation and the WMAP 'glitches'

Observations of anisotropies in the cosmic microwave background by the Wilkinson Microwave Anisotropy Probe suggest the possibility of oscillations in the primordial density perturbation. Such deviations from the usually assumed scale-free spectrum were predicted in the multiple inflation model wherein `flat direction' fields undergo rapid phase transitions due to the breaking of supersymmetry by the large vacuum energy driving inflation. This causes sudden changes in the mass of the (gravitationally coupled) inflaton and interrupts its slow roll. We calculate analytically the resulting modifications to the density perturbation and demonstrate how the oscillations arise.