  We use the high sensitivity to magnetic flux of mesoscopic conductance
fluctuations in large quantum dots to investigate changes in the
two-dimensional electron dispersion caused by an in-plane magnetic field. In
particular, changes in effective mass and the breaking of momentum reversal
symmetry in the electron dispersion are extracted quantitatively from
correlations of conductance fluctuations. New theory is presented, and good
agreement between theory and experiment is found.
