  Non-axisymmetric oscillations of differentially rotating stars are studied
using both slow rotation and Cowling approximation. The equilibrium stellar
models are relativistic polytropes where differential rotation is described by
the relativistic j-constant rotation law. The oscillation spectrum is studied
versus three main parameters: the stellar compactness $M/R$, the degree of
differential rotation $A$ and the number of maximun couplings $\ell_{\rm max}$.
It is shown that the rotational splitting of the non-axisymmetric modes is
strongly enhached by increasing the compactness of the star and the degree of
differential rotation. Finally, we investigate the relation between the
fundamental quadrupole mode and the corotation band of differentially rotating
stars.
