  Gap structure in noncentrosymmetric superconductors with spin-orbit band
splitting is studied using a microscopic model of pairing mediated by phonons
and/or spin fluctuations. The general form of pairing interaction in the band
representation is derived, which includes both the intraband and interband
pairing terms. In the case of isotropic interaction (in particular, for a
BCS-contact interaction), the interband pairing terms vanish identically at any
magnitude of the band splitting. The effects of pairing interaction anisotropy
are analyzed in detail for a metal of cubic symmetry with strong spin-orbit
coupling. It is shown that if phonons are dominant then the gaps in two bands
are isotropic, nodeless, and have in general different amplitudes. Applications
to the Li_2(Pd_{1-x},Pt_x)_3B family of noncentrosymmetric superconductors are
discussed.
