Collective oscillations of a Bose-Fermi mixture: Effect of unequal mass of Bose and Fermi particles

We investigate the effect of different mass of a Bose- and a Fermi-particle on the collective oscillations of the degenerate boson-fermion mixtures. In particular we consider the monopole and the quadrupole modes of the oscillations and study their characters and the frequencies by using variational-sum-rule approach. We find that for both the modes there exists a critical value of the ratio of boson-fermion mass below and above which the character and the frequency of the respective modes are significantly different.