Compact generation and perfect objects in homotopy categories of exact model structures
Abstract
Compact generation allows large triangulated categories to be studied through suitably small objects. For homotopy categories arising from exact model structures, a natural question is how this intrinsic notion of smallness relates to finite presentation in the underlying exact category. In this paper, we investigate this relation for hereditary projective model structures generated by finitely presented Gorenstein projective objects. We establish compact generation and study the stronger requirement that every compact object admits a finitely presented cofibrant representative. We call objects with such representatives perfect. Under local coherence and the existence of enough projectives among the finitely presented objects, the finitely presented cofibrant objects form a Frobenius category whose stable category describes the perfect objects and whose idempotent completion recovers all compact objects. The relative Q-shaped setting, for suitable small categories Q, makes explicit how these finiteness properties depend on the choice of exact structure. The pure exact structure yields a compactly generated homotopy category, called the Q-shaped pure derived category. On the other hand, the split exact structure yields the Q-shaped homotopy category, which is compactly generated only in the pure semisimple case, analogously to the classical homotopy category of complexes. Finally, for acyclic Q and for left artinian rings, we show that every compact object admits a strictly perfect representative. In particular, we establish that compact and perfect objects coincide, proving the conjecture of Holm and Jorgensen under these hypotheses.
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BibTeX
@misc{slaftsos2026compact,
title = {{Compact generation and perfect objects in homotopy categories of exact model structures}},
author = {Anastasios Slaftsos},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.36966},
eprint = {2610.36966},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.36966},
}
RIS
TY - UNPB
TI - Compact generation and perfect objects in homotopy categories of exact model structures
AU - Anastasios Slaftsos
PY - 2026
DA - 2026/10/27
PB - arXiv
DO - 10.48550/arxiv.2610.36966
UR - https://arxiv.org/abs/2610.36966
AB - Compact generation allows large triangulated categories to be studied through suitably small objects. For homotopy categories arising from exact model structures, a natural question is how this intrinsic notion of smallness relates to finite presentation in the underlying exact category. In this paper, we investigate this relation for hereditary projective model structures generated by finitely presented Gorenstein projective objects. We establish compact generation and study the stronger requirement that every compact object admits a finitely presented cofibrant representative. We call objects with such representatives perfect. Under local coherence and the existence of enough projectives among the finitely presented objects, the finitely presented cofibrant objects form a Frobenius category whose stable category describes the perfect objects and whose idempotent completion recovers all compact objects. The relative Q-shaped setting, for suitable small categories Q, makes explicit how these finiteness properties depend on the choice of exact structure. The pure exact structure yields a compactly generated homotopy category, called the Q-shaped pure derived category. On the other hand, the split exact structure yields the Q-shaped homotopy category, which is compactly generated only in the pure semisimple case, analogously to the classical homotopy category of complexes. Finally, for acyclic Q and for left artinian rings, we show that every compact object admits a strictly perfect representative. In particular, we establish that compact and perfect objects coincide, proving the conjecture of Holm and Jorgensen under these hypotheses.
ER -