Hidden infinite symmetries survive across a family of deformed field theories

Exactly solvable field theories possess infinitely many conserved charges organized into a Yangian algebra, but deforming such theories can obscure whether those charges survive. By generalizing a 1970s recursive procedure due to Brezin, Itzykson, Zinn-Justin, and Zuber, the authors derive sufficient conditions for deformed charges to still satisfy a Yangian algebra and the associated Maillet bracket structure. Applying this to a wide class of sigma models and their auxiliary-field deformations, they find Yangian symmetry intact in every case. The result provides a systematic explanation for why integrability is so robust under these deformations.