Room 6620,ITP new Building/理论物理所新楼6620报告厅

In this talk, I will connect, via tree-level double copy, any massless string amplitudes with color-ordered QFT amplitudes that are given by Cachazo-He-Yuan (CHY) formula. This can be derived by a detailed study of integration-by-part (IBP) reduction of string integrands. We present two new results in the context of heterotic and (compactified) bosonic string theories. We first find a new recursive expansion of any multitrace mixed correlator in these theories into a logarithmic part corresponding to the CHY integrand for Yang-Mills-scalar amplitudes, plus correlators with the total number of traces and gluons decreased. By iterating the expansion, we systematically reduce string correlators with any number of traces to linear combinations of Parke-Taylor factors and similarly for the cases with gluons. Based on this, we then derive a CHY formula for the corresponding DF^2+YM+phi^3 amplitudes. It is the first closed-form result for such multitrace amplitudes.