Characteristic-free bounds for the Castelnuovo-Mumford regularity

We study bounds for the Castelnuovo-Mumford regularity of homogeneous ideals in a polynomial ring in terms of the number of variables and the degree of the generators. In particular our aim is to give a positive answer to a question posed by Bayer and Mumford in [BaM], by showing that the known upper bound in characteristic zero holds true also in positive characteristic. We first analyse Giusti’s proof, which provides the result in characteristic 0, giving some insight on the combinatorial properties needed in that context. For the general case we provide a new argument which employs Bayer and Stillman criterion for detecting regularity.