2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/40856It is pointed out that $K^0$ condensation in high density matter gives rise to an extremely light Goldstone boson whose mass comes entirely from weak interactions. This implies the existence of metastable non-topological domain walls with a long lifetime. We comment on the mass of the superfluid mode if baryon number is violated.8 pagesHigh Energy Physics - PhenomenologyAstrophysicsHigh Energy Physics - TheoryNuclear TheoryLight Goldstone boson and domain walls in the $K^0$-condensed phase of high density quark mattertext