Propagation of zero sound in superfluid3He-B under magnetic field

We present a theory of zero sound propagation in super fluid³He-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 toF₂^s andF₀^a. Numerical results for the sound velocity and absorption spectrum are presented. We show that the collective modeJ = 1,J_z = 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. We show that the anomalies discovered by Ling et al. and Sounders et al. near the pair breaking edge in theq H geometry consist of theJ = 1,J_z = 0 collective mode and the pair breaking cusps in theJ_z = 0, ±2 channels.