On adiabatic invariant in generalized Galileon theories

Understand

We consider background dynamics of generalized Galileon theories in the context of inflation, where gravity and inflaton are non-minimally coupled to each other.

• In the inflaton oscillation regime, the Hubble parameter and energy density oscillate violently in many cases, in contrast to the Einstein gravity with minimally coupled inflaton.
• However, we find that there is an adiabatic invariant in the inflaton oscillation regime in any generalized Galileon theory.
• This adiabatic invariant is useful in estimating the expansion law of the universe and also the particle production rate due to the oscillation of the Hubble parameter.