  We consider relativistic superfluids where the U(1) baryon symmetry is
spontaneously broken. Using the formalism of the quantum effective action, we
show that the low-energy dynamics of the superfluid Goldstone boson is
completely determined by the equation of state. Applying the general formalism
to asymptotically high densities, we find the effective action for the
superfluid Goldstone field to leading order in alpha_s, and show that terms
containing fifth and higher powers of the Goldstone boson appear only at the
alpha_s^2 level with known coefficients.
