Title: Top-forms of Leading Singularities in Nonplanar Multi-loop Amplitudes

Speaker: Dr. Gang Chen（陈刚） (Nanjing University)

Time: 3:30PM, Sept 6 (Sunday)

Place: Theoretical Physics Division，319

Abstract：Bipartite on-shell diagram is the latest tool in constructing scattering amplitudes. In this letter we prove that an on-shell diagram process a (rational) top-form if and only if the algebraic ideal comprised of the geometrical constraints can be shifted linearly during successive Britto-Cachazo-Feng-Witten (BCFW) integrations. With a proper geometric interpretation of the constraints in the Grassmannian manifold, the top-form integration contours can thus be obtained, and understood, in a straightforward way. All top-form integrands can be obtained with the BCFW bridge decomposition chain and the soft limit, completing the top-form picture of N = 4 Super Yang-Mills (SYM) scattering amplitudes of non-planar leading singularities, on arbitrary higher loops and beyond the Maximally-Helicity-Violation (MHV) level.