Ehrenfest time and the coherent backscattering off ballistic cavities

If the Ehrenfest time tau_E of a ballistic cavity is not negligible in comparison to its dwell time tau_D, the weak localization correction to the cavity's transmission is suppressed proportional to exp(-tau_E/tau_D). At the same time, quantum interference enhances the probability of reflection into the mode of incidence by a factor two. This `enhanced backscattering' does not depend on the Ehrenfest time. We show that, in addition to the diagonal enhanced backscattering, there are off-diagonal contributions to coherent backscattering that become relevant if the Ehrenfest time is not negligible.