  The orthogonal dimer structure in the SrCu2(BO3)2 spin-1/2 magnet provides a
realization of the Shastry-Sutherland model. Using a dimer-product variational
wave function, we map out the phase diagram of the Shastry-Sutherland model
including anisotropies. Based on the variational solution, we construct a
bond-wave approach to obtain the excitation spectra as a function of magnetic
field. The characteristic features of the experimentally measured neutron and
ESR spectra are reproduced, like the anisotropy induced zero field splittings
and the persistent gap at higher fields.
