Stokes phenomenon and gravitational particle production -- How to evaluate it in practice

Understand

We revisit gravitational particle production from the Stokes phenomenon viewpoint, which helps us make a systematic way to understand asymptotic behavior of mode functions in time-dependent background.

• One of our purposes of this work is to make the method more practical for evaluation of non-perturbative particle production rate.
• In particular, with several examples of time-dependent backgrounds, we introduce some approximation methods that make the analysis more practical.
• Specifically, we consider particle production in simple expanding backgrounds, preheating after $R^2$ inflation, and a transition model with smoothly changing mass.