Exercises on derived categories, resolutions, and Brown representability

Derived categories, resolutions, and Brown representability

These notes are based on a series of five lectures given during the summer school ``Interactions between Homotopy Theory and Algebra'' held at the University of Chicago in 2004.

$Σ$-pure injectivity and Brown representability

We prove that a right $R$-module $M$ is $Σ$-pure injective if and only if $\mathrm{Add}(M)\subseteq \mathrm{Prod}(M)$. Consequently, if $R$ is a unital ring, the homotopy category $\mathbf{K}({\mathrm{Mod}\text{-} R})$ satisfies the Brown Representability Theorem if and only if the dual category has the same property. We also apply the main result to provide new characterizations for right pure-semisimple rings or to give a partial positive answer to a question of G. Bergman.

Failure of Brown representability in derived categories

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…

Tate动机导出范畴的分层

Stratification of Derived Categories of Tate Motives

本研究对特定代数闭域上混合Tate动机导出范畴的局部化张量理想分类，证明其满足Barthel-Heard-Sanders意义下的分层，核心是提出借助Brown–Adams可表示性传递分层的新技术，具备独立研究价值。