Bounding the homology of FI-modules

Abstract

The main theorem of Church-Ellenberg [arXiv:1506.01022] is a sharp bound on the homology of FI-modules, showing that the Castelnuovo-Mumford regularity of FI-modules over Z can be bounded in terms of generators and relations. We give a new proof of this theorem, inspired by earlier proofs by Li-Yu and Li. This should be read after Section 2 of Church-Ellenberg, which contains all needed terminology and background.