Confronting Cold Dark Matter Cosmologies with Strong Clustering of Lyman Break Galaxies at [CLC][ITAL]z[/ITAL][/CLC] ∼ 3

We perform a detailed analysis of the statistical significance of a concentration of Lyman break galaxies at z ~ 3 recently discovered by Steidel et al. (1997), using a series of N-body simulations with N=256³ particles in a (100)³ comoving box. While the observed number density of Lyman break galaxies at z~3 implies that they correspond to systems with dark matter halos of 10¹²M_, the resulting clustering of such objects on average is not strong enough to be reconciled with the concentration if it is fairly common; we predict one similar concentration approximately per (6~ 10) fields in three representative cold dark matter models. Considering the current observational uncertainty of the frequency of such clustering at z~3, it would be premature to rule out the models, but the future spectroscopic surveys in a dozen fields could definitely challenge all the existing cosmological models a posteriori fitted to the $z=0$ universe.