  The excitation spectrum of a S=1/2 2D triangular quantum antiferromagnet is
studied using 1/S expansion. Due to the non-collinearity of the classical
ground state significant and non-trivial corrections to the spin wave spectrum
appear already in the first order in 1/S in contrast to the square lattice
antiferromagnet. The resulting magnon dispersion is almost flat in a
substantial portion of the Brillouin zone. Our results are in quantitative
agreement with recent series expansion studies by Zheng, Fjaerestad, Singh,
McKenzie, and Coldea [PRL 96, 057201 (2006) and cond-mat/0608008].
