  Deryagin, Grigoriev, and Rubakov (DGR) have shown that in finite-density QCD
at infinite Nc the Fermi surface is unstable with respect to the formation of
chiral waves with wavenumber twice the Fermi momentum, while the BCS
instability is suppressed. We show here that at large, but finite Nc, the DGR
instability only occurs in a finite window of chemical potentials from above
Lambda_QCD to mu_critical = exp(gamma ln^2 Nc + O(ln Nc ln ln Nc))Lambda_QCD,
where gamma = 0.02173. Our analysis shows that, at least in the perturbative
regime, the instability occurs only at extremely large Nc, Nc > 1000 Nf, where
Nf is the number of flavors. We conclude that the DGR instability is not likely
to occur in QCD with three colors, where the ground state is expected to be a
color superconductor. We speculate on possible structure of the ground state of
finite-density QCD with very large Nc.
