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1 results

  • 11 - Perturbation Theory

  • from Part III - Interactions
  • Michel Talagrand
  • Book:
    What Is a Quantum Field Theory?
    Published online:
    22 February 2022
    Print publication:
    17 March 2022, pp 299-321

  • Summary

    We give a brief and basic introduction to perturbation theory. The main idea is to attempt to consider the situation of interest as a small perturbation of a simpler situation (which can be understood completely), and in particular to consider a system with a weak interaction as a perturbation of a non-interacting system. We develop the interaction picture, which allows approximating the time-evolution of an interacting system by the partial sums of the Dyson series, a fundamental tool for the sequel. We illustrate these ideas on a rudimentary model of the interaction of electrons and “photons”.