Silver blaze puzzle in 1/Nc expansions of cold and dense QCD matter

We consider quantum chromodynamics ( QCD) with Nc colors and Nf quark flavors at finite quark chemical potential mu q or isospin chemical potential mu I. We specifically address the nature of the "silver blaze" behavior in the framework of 1/ Nc expansions. Starting with the QCD partition function, we implement Veneziano's N-f/ Nc expansion to identify the density onset. We find the baryon mass MB and the pion mass m(pi) appearing from different orders of Veneziano's expansion. We argue that the confining properties are responsible for the silver blaze behavior in the region of m(pi)/ 2 < mu q < MB/ Nc. We point out, however, that Veneziano's expansion brings about a subtlety along the same line as the baryon problem in finite-density quenched lattice simulations. We emphasize that the large-Nc limit can allow for the physical ordering of MB and mp thanks to the similarity between the large- Nc limit and the quenched approximation, while unphysical ghost quarks contaminate the baryon sector if Nc is finite. We also discuss the " orientifold" large-Nc limit that does not quench quark loops.