Propagation of zero sound in superfluid 3He-B under magnetic field

The authors present a theory of zero sound propagation in superfluid 3He-B with an order parameter strongly distorted by magnetic field. A general formula of the dispersion relation for arbitrary magnetic field in the collisionless regime is derived within the weak coupling theory and under the assumption of particle-hole symmetry. The Landau parameters are taken into account up to F22 and F0a. Numerical results for the sound velocity and absorption spectrum are presented. The authors show that the collective mode J = 1, Jz = 0 yields a sizable peak in the sound absorption spectrum under weak but finite magnetic field. The quasi-particle excitations under magnetic field also exhibit cusp-like fine structures in the absorption spectrum. The authors show that the anomalies discovered by Ling et al. and Saunders et al. near the pair breaking edge in the q perpendicular H geometry consist of the J = 1, Jz = 0 collective mode and the pair breaking cusps in the Jz = 0, ± 2 channels