  We investigate spontaneous symmetry breaking within the linear sigma model
with the SU(2)xU(1) internal symmetry at finite chemical potential, which was
suggested as a model for kaon condensation in the CFL phase of dense quark
matter. One-loop corrections to the scalar field effective potential as well as
its propagator are calculated. Particular attention is paid to the type-II
Goldstone boson that appears in the Bose--Einstein condensed phase.
Furthermore, we show that the type-I Goldstone boson -- the superfluid phonon
-- is allowed to decay due to the nonlinearity of its dispersion relation at
high momentum, and determine its decay width.
