Eigenvector and eigenvalue problem for 3D bosonic model
  In this paper we reformulate free field theory models defined on the rectangular $D+1$ dimensional lattices as $D+1$ evolution models. This evolution is in part a simple linear evolution on free (``creation'' and ``annihilation'') operators. Formal eigenvectors of this linear evolution can be directly constructed, and them play the role of the ``physical'' creation and annihilation operators. These operators being completed by a ``physical'' vacuum vector give the spectrum of the evolution operator, as well as the trace of the evolution operator give a correct expression for the partition function. As an example, Bazhanov -- Baxter's free bosonic model is considered. 
I. G. Korepanov and S. M. Sergeev