Mean-field theory for the t-J model

We present a new mean-field theory for the t-J model using a representation in which singly occupied sites or spins are represented by bosons and empty sites or holes by fermions. We obtain a phase diagram which includes ferromagnetic, antiferromagnetic, spiral (with the pitch inversely proportional to the density of holes), and disordered spin-liquid phases, with a clear separation of charge and spin excitations. We comment on the conditions for obtaining superconductivity in the model