  We show that the forward limit of tree-level scattering equations with two
massive particles yields the SL(2,C)-covariant form of the one-loop scattering
equations recently proposed by Geyer et al. We clarify several properties about
these equations and the formulas at one loop. We then argue that in the
bi-adjoint scalar theory, such forward limit yields the correct one-loop
massless amplitudes, which leads to a new formula for the latter.

High Energy Physics - Theory