Seminari di gruppo IV

Md. Abhishek, "Why is the on-shell technique better than the off-shell technique to compute scattering amplitudes?"




The scattering cross section, which counts the number of scattering events, is proportional to the square of the scattering amplitude. In perturbative quantum field theory, we use Feynman diagrams to compute scattering amplitudes. Although Feynman diagrams are very efficient for a smaller number of legs and loops, the number of diagrams increases factorially with the external legs. The reason behind the complexity of Feynman diagram computation is that individual Feynman diagrams contain off-shell internal lines and are gauge-dependent. On the other hand, scattering amplitudes are only a function of on-shell quantities and are gauge-invariant. On-shell techniques to compute scattering amplitudes have made enormous progress in the last couple of decades. The main focus of on-shell computation is to evaluate the analytic expression of the final amplitude without involving the complications of off-shell computation. In this talk, I will discuss the well-known Britto-Cachazo-Feng-Witten (BCFW) on-shell recursion relation to construct a higher-point tree-level scattering amplitude from a lower-point one.