Speaker
Description
The Gell-Mann-Low relation forms the foundation of all perturbative approaches to QFT. In order to establish how perturbation theory can be consistently generalised to finite-temperature systems it is therefore necessary to understand how this relation is modified by thermal effects. In this talk I will introduce a new proposal for how this relation should be generalised, based on the non-perturbative spectral characteristics of thermal correlation functions. I will outline why the perturbative expansion in this framework resolves the two major problems of the standard real-time approach, namely the appearance of products of on-shell components, and infrared divergences in massless theories. Moreover, by using numerical lattice simulations in massive $\phi^{4}$ theory I will demonstrate that this framework provides precise finite-temperature predictions of the lattice data, in contrast to the standard perturbative approach.