Instant preheating in a scale invariant two measures theory
  The instant preheating mechanism in the framework of a scale invariant two
measures theory is studied. We introduce this mechanism into a non oscillating
inflationary model as another possible solution to the reheating of the
universe in this theory. In this framework, we consider that the model includes
two scalar matter fields, the first a dilaton field, that transforms under
scale transformations and it will be considered also as the field that drives
inflation and the second, a scalar field which will interact with the inflaton
through an effective potential. By assuming this interaction term, we obtain a
scenario of instant radiation or decay of particles according to the domain the
effective mass of the field that interacts with the inflaton. Also, we consider
a scale invariant Yukawa interaction and then after performing the transition
to the physical Einstein frame we obtain an expression for the decay rate from
our scalar field going into two fermions. Besides, from specific decay rates,
different constraints and bounds for the coupling parameters associated with
our model are found.
