Zoom virtual seminar: click here to enter the room.
I will revisit implications of elastic unitarity and extended analyticity for the S-matrix of unitary, relativistic, gapped theories in d≥3 spacetime dimensions. Elastic unitarity leads to a natural threshold expansion for the discontinuity of the scattering amplitude at low energies, as well as for the double discontinuity of the amplitude close to the leading Landau curve. Using extended analyticity, crossing and the Froissart-Gribov formula one can constrain the amplitude in terms of the threshold expansion data. One can also consider a lower bound on inelasticity for particle production at finite energy and spin. Finally, I discuss implementation of elastic unitarity in the current numerical S-matrix bootstrap program.