Spectral flow for an integrable staggered superspin chain

The flow of the low energy eigenstates of a $U_q\left[sl\right(2\left|1\right)]$ superspin chain with alternating fundamental (3) and dual ($\overline{3}$) representations is studied as function of a twist angle determining the boundary conditions. The finite size spectrum is characterized in terms of scaling dimensions and quasi momenta representing the two families of commuting transfer matrices for the model which are even and odd under the interchange $3\leftrightarrow \overline{3}$, respectively. Based on the extrapolation of our finite size data we find that under a variation of the boundary conditions from periodic to antiperiodic for the fermionic degrees of freedom levels from the continuous part of the spectrum flow into discrete levels and vice versa. (paper)