Unitarity Methods for Magnus Amplitudes

Abstract

Magnus amplitudes refer to the matrix elements of the logarithm of the $S$-matrix. Modern unitarity methods construct cut-constructible parts of scattering amplitudes without directly invoking Feynman diagrams, offering an efficient way of obtaining loop integrands for scattering amplitudes. A procedure is proposed that adapts unitarity methods to the computation of Magnus amplitudes by modifying the $i0^+$ prescriptions of scattering amplitude integrands. A sufficient condition for applying the procedure at the level of master integrals is identified.