Separated variables and wave functions for rational gl(N) spin chains in the companion twist frame

Authors: Paul Ryan and Dmytro Volin Preprint number: UUITP-49/18 We propose a basis for rational gl(N) spin chains in an arbitrary rectangular representation (S^A) that factorises the Bethe vectors into products of Slater determinants in Baxter Q-functions. This basis is constructed by repeated action of fused transfer matrices on a suitable reference state. We prove that it diagonalises the so-called B-operator, hence the operatorial roots of the latter are the separated variables. The spectrum of the separated variables is also explicitly computed and it turns out to be labelled by Gelfand-Tsetlin patterns. Our approach utilises a special choice of the spin chain twist which substantially simplifies derivations.