Ground state of ID bosons with delta interaction: link to the BCS model

The Bethe roots describing the ground-state energy of the integrable one-dimensional (ID) model of interacting bosons with weakly repulsive two-body delta interactions are seen to satisfy the set of Richardson equations appearing in the strong coupling limit of an integrable BCS pairing model. The BCS model describes boson-boson interactions with zero centre of mass momentum of pairs. It follows that the Bethe roots of the weakly interacting boson model are given by the zeros of Laguerre polynomials. The ground-state energy and the lowest excitation are obtained explicitly via the Bethe roots. A direct link has thus been established, in the context of integrable 11) models, between bosons interacting via weakly repulsive two-body delta interactions and strongly interacting BCS boson pairs.