Abstract We consider
gl2 g l 2 -invariant quantum integrable models solvable by the algebraic Bethe ansatz. We show that the form of on-shell Bethe vectors is preserved under certain twist transformations of the monodromy matrix. We also derive the actions of the twisted monodromy matrix entries on the twisted off-shell Bethe vectors.
We study the class of
o2n+1 -invariant quantum integrable models in the framework of the algebraic Bethe ansatz and propose a construction of the
o2n+1 -invariant Bethe vector in terms of the Drinfeld currents for the Yangian double
DY(o2n+1) . We calculate the action of the monodromy matrix elements on the off-shell Bethe vectors for these models and obtain recurrence relations for these vectors. The action formulas can be used to investigate scalar products of Bethe vectors in
o2n+1 -invariant models.