On the Symmetry Foundation of Double Soft Theorems

Understand

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.
• We show that soft-behaviour for type A scheme can simply be derived from single soft theorems, and are thus non-preturbatively protected.