Threshold analysis for a family of 2×2 operator matrices
Аннотация
We consider a family of 2 2 operator matrices A(k), k T 3 := (-, ] 3 , > 0, acting in the direct sum of zero-and one-particle subspaces of a Fock space. It is associated with the Hamiltonian of a system consisting of at most two particles on a three-dimensional lattice Z 3 , interacting via annihilation and creation operators. We find a set := {k (1) , ..., k (8) } T 3 and a critical value of the coupling constant to establish necessary and sufficient conditions for either z = 0 = min kT 3 ess(A(k)) ( or z = 27/2 = max kT 3 ess(A(k)) is a threshold eigenvalue or a virtual level of A(k (i) ) for some k (i) .