New approach for amplitudes with multiple fermion lines * *Supported by the National Natural Science Foundation of China (12135013, 11975242); It was also supported in part by National Key Research and Development Program of China (2020YFA0406400)

Abstract

A new approach for tree-level amplitudes with multiple fermion lines is presented. It primarily focuses on the simplification of fermion lines. By calculating two vectors recursively without any matrix multiplications, the result of a fermion line is reduced to a very compact form depending only on the two vectors. Comparisons with other packages are presented, and the results show that our package FDC provides a very good performance in the processes of multiple fermion lines with this new approach and some other improvements. A further comparison with WHIZARD shows that this new approach has a competitive efficiency in computing pure amplitude squares without phase space integration.