Significant cluster correlations at 30 h^-1 Mpc: Can standard models be ruled out?

We compute the cluster autocorrelation function, ξ_c(r), of an extended, complete sample of 220 rich (R ≥ 1) Abell clusters with measured redshifts. We correct for projection contamination and pay special attention to estimating the random errors, aiming at rejecting certain theoretical models. While the observed ξ_c in the range r < 20 h^-1 Mpc is in agreement with the predictions of CDM and textures models, we find an excess over both theories in the range 20 h^-1 Mpc ≤ r ≤ 40 h^-1 Mpc, significant at beyond the 3 σ level. Assuming that the observed ξ_c below 30 h^-1 Mpc represents the true correlations, the hypothesis that ξ_c vanishes right beyond this scale can be rejected with similar confidence. These results are in agreement with our earlier findings from the angular correlation function of the complete Abell and ACO catalogs. Possible remaining biases and ways out for these models are discussed.