The number and location of eigenvalues for the two-particle Schrödinger operators on lattices

Abstract: We study the Schr\"odinger operators $H_{\gamma \lambda \mu}(K)$, $K\in\T$ being a fixed (quasi)momentum of the particles pair, associated with a system of two identical bosons on the one-dimensional lattice $\mathbb{Z}$, where the real quantities $\gamma$, $\lambda$ and $\mu$ describe the interactions between pairs of particles on one site, two nearest neighboring sites and next two neighboring sites, respectively. We found a partition of the three-dimensional space $(\gamma, \lambda,\mu)$ of interaction parameters into connected components and the exact number of eigenvalues of this operator that lie below and above the essential spectrum, in each component. Moreover, we show that for any $K\in\T^d$ the number of eigenvalues of $H_{\gamma\lambda\mu}(K)$ is not less than the corresponding number of eigenvalues of $H_{\gamma\lambda\mu}(0)$.