https://doi.org/10.1140/epjc/s10052-020-8154-9
Special Article – Tools for Experiment and Theory
QED and QCD helicity amplitudes in parton-shower gauge
1
Institute of Science and Engineering, Shimane University, Matsue, 690-8504, Japan
2
KEK Theory Center, Tsukuba, 305-0801, Japan
3
KEK and Sokendai, Tsukuba, 305-0801, Japan
4
Present address: Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, Kashiwa, 277-8583, Japan
5
Faculty of Education, Iwate University, Morioka, Iwate, 020-8550, Japan
* e-mail: mawatari@iwate-u.ac.jp
Received:
18
March
2020
Accepted:
16
June
2020
Published online:
29
June
2020
We introduce photon and gluon propagators in which the scalar polarization component is subtracted systematically by making use of the BRST invariance of the off-shell vector boson created from physical on-shell states. The propagator has the light-cone gauge form, where the spacial component of the gauge vector points along the negative of the off-shell vector boson momentum. We call the gauge as parton-shower gauge, since in collinear configurations the absolute value squared of each Feynman amplitude reproduces all the singular behaviors of the corresponding parton shower in this gauge. We introduce new HELAS codes that can be used to calculate the tree-level helicity amplitudes of arbitrary QED and QCD processes by using MadGraph. The absence of subtle gauge cancellation among Feynman amplitudes allows numerical codes to evaluate singular behaviors accurately, and helps us gaining physical insights on interference patterns.
© The Author(s), 2020
