Goldstone boson currents in a kaon condensed color-flavor locked phase

We study the stability of the kaon condensed color-flavor locked (CFL) phase of dense quark matter with regard to the formation of a nonzero Goldstone boson current. In the kaon condensed phase there is an electrically charged fermion which becomes gapless near µ_s⁽¹⁾~=1.35Delta and a neutral fermion which becomes gapless near µ_s⁽²⁾~=1.61Delta. Here, µ_s=m_s²/(2p_F) is the shift in the Fermi energy due to the strange quark mass m_s and Delta is the gap in the chiral limit. The transition to the gapless phase is continuous at µ_s⁽¹⁾ and first order at µ_s⁽²⁾. We find that the magnetic screening masses are real in the regime µ_s<µ_s⁽²⁾, but some screening masses are imaginary for µ_s>µ_s⁽²⁾. We show that there is a very weak current instability for µ_s>µ_s⁽¹⁾ and a more robust instability in a small window near µ_s⁽²⁾. We show that in the Goldstone boson current phase all components of the magnetic screening mass are real. There is a range of values of µ_s below 2Delta in which the magnetic gluon screening masses are imaginary but the phase is stable with respect to electrically neutral fluctuations of the gauge field.

©2007 The American Physical Society