Boson Models with Interactions of Arbitrary Order

The paper considers quantal many-boson systems that are described by a rotationally invariant and boson-number conserving Hamiltonian. The properties of a generic model are studied, which treats N bosons of p different kinds with non-zero angular momenta ℓ1,ℓ2,…,ℓp, possibly augmented with a (number of) scalar s boson(s). The order k of the interaction between the bosons is arbitrary, and closed formulas are given for matrix elements between N-boson states for any k if p=1 and p=2. A recursive procedure is defined for arbitrary k and p. With the expressions derived in the paper, it is possible to express symbolically a Hamiltonian matrix element between N-boson states as a linear combination of k-body interaction matrix elements. More generally, the formulas allow the evaluation of matrix elements of tensor operators that are not necessarily scalar nor boson-number conserving. The numerical implementation of the formalism is discussed and illustrated with a few examples.