Modes of superfluid 3He in the entire hydrodynamic region

Abstract Dispersion relations for hydrodynamic modes are normally derived in the limit of small damping. This limit covers the entire hydrodynamic region as long as the region conincides with the small damping region (e.g., in 4 He-II). This is not the case in 3.5. Superfluid 3 He. In this paper the dispersion relations of second sound and sq-mode are generalized throughout the hydrodynamic region. It might have experimental implications for any 3He experiment dealing with frequencies of Hz and higher. They are discussed in detail.