Dressing chains and the spectral theory of the Schrödinger operator (Q1335884)

The authors consider the sequence of Schrödinger operators \[ L_ i = - (D + f_ i) (D-f_ i) = - \Delta + u_ i, \quad u_ i = f_ i' + f^ 2_ i, \tag{1} \] where the functions \(f_ i\) satisfy the following system of ordinary differential equations, \[ (f_ i + f_{i+1})' = f_ i^ 2 - f_{i+1}^ 2 + \alpha_ i, \quad f_{i+N} = f_ i, \quad \alpha_{i+N} = \alpha_ i, \tag{2} \] \(1 \leq i \leq N\), called a dressing chain. Here \(\alpha_ 1, \dots, \alpha_ N\) are constant parameters. The authors study the system (2) and prove, for example, that if \(N\) is odd and \(\alpha_ 1 + \cdots + \alpha_ N = 0\) then the chain (2) is a completely integrable Hamiltonian system. The spectral properties of the corresponding Schrödinger operators (1) are investigated as well.