Dispersion induced splitting of the collective mode spectrum in A-phase of superfluid He

The whole collective mode spectrum in A-phase of superfluid ³He with dispersion corrections is calculated. The degeneracy of clapping-modes depends on the direction of the collective mode momentum k with respect to the vector l (mutual orbital moment of Cooper pairs), namely: the mode degeneracy remains the same as in case of zero momentum k for k∥l only. For any other directions there is a three-fold splitting of these modes, which reaches maximum for k⊥l. The obtained results means that new interesting features can be observed in ultrasound experiments in axial-phase: the change of the number of peaks in ultrasound absorption into clapping-mode. Single peak, observed for these modes in axial-phase by Ling et al. R. Ling, W. Wojtanowski, J. Saunders, E.R. Dobbs, J. Low Temp. Phys. 78 (1990) 187] will split into three peaks under change the ultrasound direction with respect to the vector l.