PUB - Publikationen an der Universität Bielefeld

We revisit the issue of color neutrality in effective model descriptions ofdense quark matter based on global color symmetry. While the equilibriumthermodynamics of such models is now well understood, we examine the collectivemodes, focusing on the fluctuations of the order parameter. We point out thatthe constraint of color neutrality must be carefully generalized in order toobtain physically consistent and well-defined results. Particularly importantis that the collective modes associated with order parameter fluctuationscouple to charge density fluctuations in the neutral medium. We start byproving explicitly that, in contrast to claims made previously in literature,Nambu-Goldstone bosons of spontaneously broken global color symmetry remainexactly massless even after imposing the color neutrality constraint. As thenext step, we make the argument general by using effective field theory. Wethen employ the high-density approximation to calculate the couplings in theeffective Lagrangian and thus the Nambu-Goldstone boson dispersion relations.