Discreteness and cone finiteness for triangulated categories

Let D\mathsf{D} be a Hom-finite Krull--Schmidt triangulated category and let H\mathsf{H} be the heart of a bounded tt-structure. The category D\mathsf{D} is H\mathsf{H}-discrete when, for every function v ⁣:ZK0(H)v\colon\mathbb{Z}\to K_0(\mathsf{H}), only finitely many objects DDD\in\mathsf{D} satisfy [Hi(D)]=v(i)[H^i(D)]=v(i) for all iZi\in\mathbb{Z}. Discreteness conjectures.

  1. If D\mathsf{D} is H\mathsf{H}-discrete, then all bounded hearts in D\mathsf{D} are discrete.
  2. If D\mathsf{D} is H\mathsf{H}-discrete, then (D,H)(\mathsf{D},\mathsf{H}') is H\mathsf{H}'-discrete for every bounded heart H\mathsf{H}'.
  3. If D\mathsf{D} is H\mathsf{H}-discrete and H\mathsf{H} is finite, then all bounded hearts are finite.
  4. D\mathsf{D} is H\mathsf{H}-discrete if and only if D\mathsf{D} is cone finite.

These statements are expected to hold in general and are proved in the source for derived-discrete algebras. The source also notes that discreteness with respect to a bounded heart does not force Hom boundedness, so the hypotheses distinguish different finiteness properties.

Sources & referencesView supporting material

Primary source

Nathan Broomhead, David Pauksztello and David Ploog, “Discrete triangulated categories”, arXiv:1512.01482 (2018).

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