Spectrum of transfer matrix for $U_q(B_n)$-invariant $A^{(2)}_{2n}$ open   spin chain
  We propose an expression for the eigenvalues of the transfer matrix for the $U_q(B_n)$-invariant open quantum spin chain associated with the fundamental representation of $A^{(2)}_{2n}$. By assumption, the Bethe Ansatz equations are ``doubled'' with respect to those of the corresponding closed chain with periodic boundary conditions. We verify that the transfer matrix eigenvalues have the correct analyticity properties and asymptotic behavior. We also briefly discuss the structure of the eigenstates of the transfer matrix. 
Simone Artz, Luca Mezincescu, and Rafael I. Nepomechie