IAS Amplitudes Group Meeting

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Abstract: The S-matrix bootstrap aims at constraining massive scattering amplitudes in quantum field theory (QFT) based on general principles, such as unitarity and crossing symmetry. I will review some old cornerstone results in the S-matrix bootstrap. Namely, the Froissart bound on the growth of the total cross section; Gribov's theorem which invalidates the black disk diffraction model in QFT but, more generally, constrains the Regge behavior of the amplitude; and the Aks theorem on the necessity of particle production in d>2. Most of these theorems result from two-particle unitarity, while very little is still known about multi-particle unitarity. If time permits I will show a new result, namely that the non-perturbative amplitude has an accumulation of Landau singularities between the 4- and 6-particle thresholds on the physical sheet (based on https://arxiv.org/abs/2111.12100).