Phys. Lett. B  822, 136698 (2021)

Infrared photons and asymptotic symmetries

Zhengwen Liu¹ and Pujian Mao^2,*

1 Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, 22607 Hamburg, Germany

2 Center for Joint Quantum Studies and Department of Physics, School of Science, Tianjin University, 135 Yaguan Road, Tianjin 300350, China

* Corresponding Authors:  Z. Liu (Email: zhengwen.liu@desy.de )  P. Mao (Email: pjmao@tju.edu.cn )

Abstract

S-matrix elements exhibit universal factorization when multiple infrared photons are emitted in scattering processes. We explicitly show that the leading soft factorization of tree-level amplitudes with the emission of any number of soft photons can be interpreted as the Ward identity of the asymptotic symmetry of gauge theory.