On Preheating after Inflation in Scalar-Tensor Theories of Gravity

In this work, the preheating mechanism is investigated after inflation in general scalar-tensor theories of gravity. In the present scenario, two-field scenario is considered and then derived the potential of exponential and hyperbolic tangent forms. The evolution of the background system is studied when the back reaction on the background field is neglected. The particle production due to parametric resonances in both models is examined. It is found that in Minkowski space the stage of parametric resonances can be described by the Mathieu equation. Finally, parametric resonances in the models are sufficiently broad possible for the exponential growth of the number of particles are demonstrated. The case in which the expansion of space is taken into account is also discussed.