  The application of the Schwinger-boson transformation to quantum Heisenberg
magnets is briefly reviewed, beginning with the derivation of a rotationally
invariant mean-field theory. The inclusion of Gaussian fluctuations is
discussed in some detail for a general (non-Bravais) lattice, extending
available results for simple lattices. Numerical results are presented for the
ground-state energy of the Shastry-Sutherland model, and possible future
refinements of the method are outlined.
