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Regular Seminar Andrea Marzolla (Bruxelles U.)
room G.O. Jones 610
Poincaré invariance imposes strong non-perturbative constraints on the dependence of scattering amplitudes on the kinematical variables. For massless external states, Benincasa and Cachazo have shown that the 3-point amplitude is fully determined up to a constant (the coupling). We extend their approach, based on the spinor-helicity formalism, to time-like momenta, and we find that, even when massive external states are involved, the functional form of the 3-point amplitude is fully determined, up to (several) constants. In this talk I review the derivation in the massless case, enlightening the role of the little group covariance of the amplitude in constraining its functional form, and the particularly simple form that these constraints get in the spinor language. Then I will show how to extend this procedure to the massive case, deriving the constraining equations for the massive little group, and eventually showing the expressions for 3-point amplitudes involving one, two, or three massive particles.