２００１年度 東大駒場原子核理論セミナー

Structural Change of Cooper Pairs and Momentum-dependent Gap in Color Superconductivity

The two-flavor color superconductivity is studied with a special attention to the {\it spatial}-momentum dependence of the gap and to the {\it spatial}-structure of Cooper pairs. The gap at extremely high baryon density ($\sim {\cal O}(10^{10} \rho_0)$ with $\rho_0$ being the normal nuclear matter density) is shown to have a sharp peak near the Fermi surface due to the weak-coupling nature of QCD. On the other hand, the gap is a smooth function of the momentum at lower densities ($\sim {\cal O}(10 \rho_0)$) due to strong color magnetic and electric interactions. To study the structural change of Cooper pairs from high density to low density, quark correlations in the color superconductor are studied in the momentum space and in the coordinate space. The size of the Cooper pair is shown to become comparable to the averaged inter-quark distance at low densities. Also, effects of the momentum-dependent quark-gluon vertex and the coupling to the antiquark pairing, which are both small at high density, are shown to be non-negligible at low densities. These features are highly contrasted to the standard BCS superconductivity in metals.