Precessing domains and the Castaing instability in confined alkali-metal gases

We explore the analogy between two-component quantum alkali-metal gases and spin-polarized helium systems. Recent experiments in trapped gases are put into the frame of the existing theory for the Castaing instability in transverse channels and the formation of homogeneous precessing domains in spin-polarized systems. Analogous effects have already been observed in spin-polarized ³He and ³He-⁴He mixture systems. The threshold effect of the confining potential on the instability is analyzed. Additional experimental possibilities for the observation of a transverse instability in a trap are discussed.