Hearts of t-structures in the derived category of a commutative Noetherian ring

preprint2015arXivOpen access

Abstract

Let RR be a commutative Noetherian ring and let D(R)\mathcal D(R) be its (unbounded) derived category. We show that all compactly generated t-structures in D(R)\mathcal D(R) associated to a left bounded filtration by supports of Spec(R)(R) have a heart which is a Grothendieck category. Moreover, we identify all compactly generated t-structures in D(R)\mathcal D(R) whose heart is a module category. As geometric consequences for a compactly generated t-structure (U,U⊥[1])(\mathcal{U},\mathcal{U}^\perp [1]) in the derived category D(X)\mathcal{D}(\mathbb{X}) of a Noetherian scheme X\mathbb{X}, we get the following: 1) If the sequence (U[−n]∩D≤0(X))n∈N(\mathcal{U}[-n]\cap\mathcal{D}^{\leq 0}(\mathbb{X}))_{n\in\mathbb{N}} is stationnary, then the heart H\mathcal{H} is a Grothendieck category; 2) If H\mathcal{H} is a module category, then H\mathcal{H} is always equivalent to Qcoh(Y)\text{Qcoh}(\mathbb{Y}), for some affine subscheme Y⊆X\mathbb{Y}\subseteq\mathbb{X}; 3) If X\mathbb{X} is connected, then: a) when ⋂k∈ZU[k]=0\bigcap_{k\in\mathbb{Z}}\mathcal{U}[k]=0, the heart H\mathcal{H} is a module category if, and only if, the given t-structure is a translation of the canonical t-estructure in D(X)\mathcal{D}(\mathbb{X}); b) when X\mathbb{X} is irreducible, the heart H\mathcal{H} is a module category if, and only if, there are an affine subscheme Y⊆X\mathbb{Y}\subseteq\mathbb{X} and an integer mm such that U\mathcal{U} consists of the complexes U∈D(X)U\in\mathcal{D}(\mathbb{X}) such that the support of Hj(U)H^j(U) is in X∖Y\mathbb{X}\setminus\mathbb{Y}, for all j>mj>m.

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