Failure of Brown representability in derived categories
Abstract
Let T be a triangulated category with coproducts, C the full subcategory of compact objects in T. If T is the homotopy category of spectra, Adams proved the following in [Adams71]: All contravariant homological functors C --> Ab are the restrictions of representable functors on T, and all natural transformations are the restrictions of morphisms in T. It has been something of a mystery, to what extent this generalises to other triangulated categories. In [Neeman97], it was proved that Adams' theorem remains true as long as C is countable, but can fail in general. The failure exhibited was that there can be natural transformations not arising from maps in T. A puzzling open problem remained: Is every homological functor the restriction of a representable functor on T? In a recent paper, Beligiannis made some progress. But in this article, we settle the problem. The answer is no. There are examples of derived categories T = D(R) of rings, and contravariant homological functors C --> Ab which are not restrictions of representables.
Cite
@article{arxiv.math/0001056,
title = {Failure of Brown representability in derived categories},
author = {J. Daniel Christensen and Bernhard Keller and Amnon Neeman},
journal= {arXiv preprint arXiv:math/0001056},
year = {2017}
}
Comments
22 pages, to appear in Topology. http://jdc.math.uwo.ca Lots of minor revisions. This version should closely match the published version