QCD at finite baryon density: nucleon droplets and color superconductivity
Abstract
We use a variational procedure to study finite density QCD in an approximation in which the interaction between quarks is modelled by that induced by instantons. We find that uniform states with conventional chiral symmetry breaking have negative pressure with respect to empty space at all but the lowest densities, and are therefore unstable. This is a precisely defined phenomenon which motivates the basic picture of hadrons assumed in the MIT bag model, with nucleons as droplets of chiral symmetry restored phase. At all densities high enough that the chirally symmetric phase fills space, we find that color symmetry is broken by the formation of a <qq> condensate of quark Cooper pairs. A plausible ordering scheme leads to a substantial gap in a Lorentz scalar channel involving quarks of two colors, and a much smaller gap in an axial vector channel involving quarks of the third color.
 Publication:

Physics Letters B
 Pub Date:
 March 1998
 DOI:
 10.1016/S03702693(98)000513
 arXiv:
 arXiv:hepph/9711395
 Bibcode:
 1998PhLB..422..247A
 Keywords:

 High Energy Physics  Phenomenology;
 High Energy Physics  Theory;
 Nuclear Theory
 EPrint:
 13 pages, LaTeX, uses revtex. Typographical corrections, references revised