Diquark condensation at strong coupling

The possibility of diquark condensation at sufficiently large baryon chemicalpotential and zero temperature is analyzed in QCD at strong coupling. Inagreement with other strong coupling analysis, it is found that a first orderphase transition separates a low density phase with chiral symmetryspontaneously broken from a high density phase where chiral symmetry isrestored. In none of the phases diquark condensation takes place as anequilibrium state, but, for any value of the chemical potential, there is ametastable state characterized by a non-vanishing diquark condensate. Theenergy difference between this metastable state and the equilibrium statedecreases with the chemical potential and is minimum in the high density phase.The results indicate that there is attraction in the quark-quark sector also atstrong coupling, and that the attraction is more effective at high baryondensity, but for infinite coupling it is not enough to produce diquarkcondensation. It is argued that the absence of diquark condensation is not apeculiarity of the strong coupling limit, but persists at sufficiently largefinite couplings.Comment: 10 pages, 2 figures. An important discussion concerning the extension of the results to finite couplings adde