Twisted Yangian symmetry of the open Hubbard model
  We show that, in the open Hubbard model with integrable boundary conditions, the bulk Yangian symmetry is broken to a twisted Yangian. We prove that the associated charges commute with the Hamiltonian and the reflection matrix, and that they form a coideal subalgebra. 
Alejandro De La Rosa Gomez and Niall J. MacKay
hep-th cond-mat.str-el math.QA