On the symmetry foundation of double soft theorems

Li, Zhi-Zhong (Department of Physics and Astronomy, National Taiwan University, Taipei, 10617, Taiwan) ; Lin, Hung-Hwa  (Department of Physics and Astronomy, National Taiwan University, Taipei, 10617, Taiwan) ; Zhang, Shun-Qing (Department of Physics and Astronomy, National Taiwan University, Taipei, 10617, Taiwan)

07 December 2017

Abstract: Double-soft theorems, like its single-soft counterparts, arises from the underlying symmetry principles that constrain the interactions of massless particles. While single soft theorems can be derived in a non-perturbative fashion by employing current algebras, recent attempts of extending such an approach to known double soft theorems has been met with difficulties. In this work, we have traced the difficulty to two inequivalent expansion schemes, depending on whether the soft limit is taken asymmetrically or symmetrically, which we denote as type A and B respectively. The soft-behaviour for type A scheme can simply be derived from single soft theorems, and are thus non-perturbatively protected. For type B, the information of the four-point vertex is required to determine the corresponding soft theorems, and thus are in general not protected. This argument can be readily extended to general multi-soft theorems. We also ask whether unitarity can be emergent from locality together with the two kinds of soft theorems, which has not been fully investigated before.


Published in: JHEP 1712 (2017) 032
Published by: Springer/SISSA
DOI: 10.1007/JHEP12(2017)032
arXiv: 1710.00480
License: CC-BY-4.0



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