  We investigate the effect of ring-exchange on the ground-state properties and
magnetic excitations of the $S = 1/2$ Heisenberg model on the anisotropic
triangular lattice with ring-exchange at $T = 0$ using linear spin-wave theory.
Classically, we find stable N\'{e}el, spiral and collinear magnetically ordered
phases. Upon including quantum fluctuations to the model, linear spin-wave
theory shows that ring exchange induces a large quantum disordered region in
the phase diagram, completely wiping out the classically stable collinear
phase. Analysis of the spin-wave spectra for each of these three models
demonstrates that the large spin-liquid phase observed in the full model is a
direct manifestation of competing classical orders. To understand the origin of
these competing phases we introduce models where either the four spin
contributions from ring exchange, or the renormalization of the Heisenberg
terms due to ring exchange are neglected. We find that these two terms favor
rather different physics.
