Speaker
Description
Divergence in perturbative expansions is where interesting physics takes place. Particle production on time-dependent backgrounds, as one such example, is interpreted as transition from one vacuum to another. In this talk, I establish that several conceptual issues in the conventional approach to particle production in cosmology may be eliminated by fully employing the exact WKB methodology, a resummation technique of the standard (divergent) WKB series solutions. Canonical quantization and defining vacuum are performed with respect to the resummed mode functions. The correct results are shown to be reproduced without resorting to special functions or approximations, if the quantity called the Voros coefficient, which plays an important role to renormalize the asymptotic vacuum states, is properly incorporated.