In the present talk, we will discuss how we understand a three page note from Quillen's notebook where he tries to make sense of the technique of "adding counterterms to the Lagrangian to remove the infinities" used in renormalized perturbation theory. Then we explain what the counter-terms are in the situation of a quantized fermion field, interacting with a gauge field treated as an external field. Our discussion will also be very much inspired by I.M. Singer's lecture on families of Dirac operators with application to physics.
This talk is part of series of talks affiliated with the virtual Mittag-Leffler workshop "Scattering, microlocal analysis and renormalization", organized by Claudio Dappiaggi, Jacob Schach Møller and Michal Wrochna. The full schedule can be found at: