2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/42253In this talk, I try to show that the sign problem of dense QCD is due to modes whose frequency is higher than the chemical potential. An effective theory of quasi-quarks near the Fermi surface has a positive measure in the leading order. The higher-order corrections make the measure complex, but they are suppressed as long as the chemical potential is sufficiently larger than $Λ_{\rm QCD}$. As a consequence of the positivity of the effective theory, we can show that the global vector symmetries except the U(1) baryon number are unbroken at asymptotic density.6 pages, no figures, contribution to Strong and Electroweak Matter '02 (Heidelberg)High Energy Physics - Phenomenologytext