Preheating with the Brakes On: The Effects of a Speed Limit
  We study preheating in models where the inflaton has a non-canonical kinetic
term, containing powers of the usual kinetic energy. The inflaton field
oscillating about its potential minimum acts as a driving force for particle
production through parametric resonance. Non-canonical kinetic terms can impose
a speed limit on the motion of the inflaton, modifying the oscillating inflaton
profile. This has two important effects: it turns a smooth sinusoidal profile
into a sharp saw-tooth, enhancing resonance, and it lengthens the period of
oscillations, suppressing resonance. We show that the second effect dominates
over the first, so that preheating with a non-canonical inflaton field is less
efficient than with canonical kinetic terms, and that the expansion of the
Universe suppresses resonance even further.
