IAS Physics Group Meeting

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Abstract: In this talk, we will review three methods for cancelling infrared divergences in quantum field theories order-by-order in perturbation theory: i) by computing sufficiently inclusive cross sections, ii) by modifying the definition of the S-matrix, and iii) by dressing the scattering states using the coherent-state formalism. First, we explore which processes need to be summed over in order to obtain finite cross sections. Next, we discuss how theories with massless particles break the traditional assumptions about free evolution of scattering states at asymptotic times, leading to infrared-divergences. We show how to incorporate these interactions into a redefinition of the S-matrix and thereby obtain finite amplitudes. Finally, we show how these finite amplitudes can be thought of as scattering between coherent states, and connect to their physical interpretation.