Research On The On Shell Methods For Scattering Amplitudes

This paper presents several developments and applications of on-shell meth-ods to calculate scattering amplitudes. At tree level, we first introduce the con-struction of amplitudes by factorization limits, and then propose a more system-atic and efficient approach, the multi-step BCFW recursion relations, to resolve the problem of boundary contributions in BCFW recursion relation. At loop level, we generalize the unitarity cut method for one-loop amplitudes to two-loop cases, provide a feasible scheme to identify the basis of two-loop Feynman integrals.