Secular growths and their relation to equilibrium states in perturbative QFT

Abstract

In the perturbative treatment of interacting quantum field theories, if the interaction Lagrangian changes adiabatically in time, secular growths may appear in the truncated perturbative series also when the Lagrangian has returned to be constant. If this happens, the perturbative approach does not furnish reliable results. In this talk we show that these effects are avoided for a QFT on Minkowski spacetime, if the interaction Lagrangian is spatially compact and for a large family of background states. In particular, this family of background states for which secular growths are absent is characterized and for equilibrium states the possibility of removing the spacetime cutoff in connection with the thermalisation process is further presented. The content of the talk is based on a joint work together with Nicola Pinamonti and Leonardo Sangaletti.