Separable integral extensions and plus closure

Abstract

Let R be an excellent local domain of positive characteristic, and R^+ denote the integral closure of R in an algebraic closure of its fraction field. Hochster and Huneke proved that R^+ is a big Cohen-Macaulay algebra for R, and asked if there is a smaller R-algebra with the Cohen-Macaulay property. In this paper we establish the existence of a smaller big Cohen-Macaulay algebra which is, moreover, a separable extension.