  The yielding behaviour of hard sphere glasses under large amplitude
oscillatory shear has been studied by probing the interplay of Brownian motion
and shear-induced diffusion at varying oscillation frequencies. Stress,
structure and dynamics are followed by experimental rheology and Browian
Dynamics simulations. Brownian motion assisted cage escape dominates at low
frequencies while escape through shear-induced collisions at high ones, both
related with a yielding peak in\ $G^{\prime \prime}$. At intermediate
frequencies a novel, for HS glasses, double peak in $G^{\prime \prime}$ is
revealed reflecting both mechanisms. At high frequencies and strain amplitudes
a persistent structural anisotropy causes a stress drop within the cycle after
strain reversal, while higher stress harmonics are minimized at certain strain
amplitudes indicating an apparent harmonic response.
