dorsal/arxiv
View SchemaDefinable functors and Brown--Adams representability
| Authors | Isaac Bird |
|---|---|
| Categories | |
| ArXiv ID | 2601.09443vv1 |
| URL | https://arxiv.org/abs/2601.09443 |
| License | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ |
Abstract
The question of when the derived category of a ring satisfies Brown--Adams representability is revisited via studying the transfer of pure homological dimension along definable functors: it is shown that, for any ring, the pure global dimension of the derived category is at least the pure global dimension of the ring; expanding results of Beligiannis and Keller-Christensen-Neeman. This result is obtained by constructing `change of category' isomorphisms of PExt groups across definable functors. The same isomorphisms illustrate circumstances when one can transfer the property of Brown--Adams representability. We demonstrate how these methods can be used to test whether certain derived category of quasi-coherent sheaves are a Brown category. We also make an investigation into the structure of derived categories of von Neumann regular rings, which are shown in many cases to control Brown--Adams representability; this includes a new proof of the telescope conjecture, and a new and short proof that a coherent ring satisfies Freyd's (strong) generating hypothesis if and only if it is von Neumann regular.
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"date_created": "2026-02-17T05:53:20.331000Z",
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"abstract": "The question of when the derived category of a ring satisfies Brown--Adams representability is revisited via studying the transfer of pure homological dimension along definable functors: it is shown that, for any ring, the pure global dimension of the derived category is at least the pure global dimension of the ring; expanding results of Beligiannis and Keller-Christensen-Neeman. This result is obtained by constructing `change of category\u0027 isomorphisms of PExt groups across definable functors. The same isomorphisms illustrate circumstances when one can transfer the property of Brown--Adams representability. We demonstrate how these methods can be used to test whether certain derived category of quasi-coherent sheaves are a Brown category. We also make an investigation into the structure of derived categories of von Neumann regular rings, which are shown in many cases to control Brown--Adams representability; this includes a new proof of the telescope conjecture, and a new and short proof that a coherent ring satisfies Freyd\u0027s (strong) generating hypothesis if and only if it is von Neumann regular.",
"arxiv_id": "2601.09443",
"authors": [
"Isaac Bird"
],
"categories": [
"math.RT",
"math.AT",
"math.CT"
],
"license": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
"title": "Definable functors and Brown--Adams representability",
"url": "https://arxiv.org/abs/2601.09443",
"version": "v1"
},
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