We demonstrate that in the strong coupling limit (the superconducting gap Δ is as large as the chemical potential μ), which is relevant to the high-Tc superconductivity, the correlation corrections to the gap and critical temperature are about 10\% of the corresponding mean field approximation values. For the weak coupling (Δ≪μ) the correlation corrections are very large: of the order of 100\% of the corresponding mean field values.
@article{arxiv.cond-mat/9503175,
title = {Many Body Correlation Corrections to Superconducting Pairing in Two Dimensions.},
author = {M. Yu. Kuchiev and O. P. Sushkov},
journal= {arXiv preprint arXiv:cond-mat/9503175},
year = {2009}
}