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Proceedings of the 44th Symposium on Ring Theory and ...

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ALGEBRAIC STRATIFICATIONS OF DERIVED MODULE<br />

CATEGORIES AND DERIVED SIMPLE ALGEBRAS<br />

DONG YANG<br />

Abstract. In this note I will survey <strong>on</strong> some recent progress in <str<strong>on</strong>g>the</str<strong>on</strong>g> study <str<strong>on</strong>g>of</str<strong>on</strong>g> recollements<br />

<str<strong>on</strong>g>of</str<strong>on</strong>g> derived module categories.<br />

Key Words: Recollement, Algebraic stratificati<strong>on</strong>, Derived simple algebra.<br />

2010 Ma<str<strong>on</strong>g>the</str<strong>on</strong>g>matics Subject Classificati<strong>on</strong>: 16E35.<br />

The noti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> recollement <str<strong>on</strong>g>of</str<strong>on</strong>g> triangulated categories was introduced in [5] as an analogue<br />

<str<strong>on</strong>g>of</str<strong>on</strong>g> short exact sequence <str<strong>on</strong>g>of</str<strong>on</strong>g> modules or groups. In representati<strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g>ory <str<strong>on</strong>g>of</str<strong>on</strong>g> algebras it<br />

provides us with reducti<strong>on</strong> techniques, which have proved very useful, for example, in<br />

• proving c<strong>on</strong>jectures <strong>on</strong> homological dimensi<strong>on</strong>s, see [9];<br />

• computing homological invariants, see [11, 12];<br />

• classifying t-structures, see [14].<br />

In this note I will survey <strong>on</strong> some recent progress in <str<strong>on</strong>g>the</str<strong>on</strong>g> study <str<strong>on</strong>g>of</str<strong>on</strong>g> recollements <str<strong>on</strong>g>of</str<strong>on</strong>g> derived<br />

module categories.<br />

1. Recollements<br />

Let k be a field. For a k-algebra A denote by D(A) = D(Mod A) <str<strong>on</strong>g>the</str<strong>on</strong>g> (unbounded)<br />

derived category <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> category Mod A <str<strong>on</strong>g>of</str<strong>on</strong>g> right A-modules. The objects <str<strong>on</strong>g>of</str<strong>on</strong>g> D(A) are<br />

complexes <str<strong>on</strong>g>of</str<strong>on</strong>g> right A-modules. The category D(A) is triangulated with shift functor Σ<br />

being <str<strong>on</strong>g>the</str<strong>on</strong>g> shift <str<strong>on</strong>g>of</str<strong>on</strong>g> complexes. See [10] for a nice introducti<strong>on</strong> <strong>on</strong> derived categories.<br />

A recollement <str<strong>on</strong>g>of</str<strong>on</strong>g> derived module categories is a diagram <str<strong>on</strong>g>of</str<strong>on</strong>g> derived module categories<br />

<strong>and</strong> triangle functors<br />

(1.1)<br />

i ∗<br />

j !<br />

D(B) i ∗ =i !<br />

D(A) j ! =j ∗ D(C),<br />

i !<br />

j ∗<br />

where A, B <strong>and</strong> C are k-algebras, such that<br />

(1) (i ∗ , i ∗ = i ! , i ! ) <strong>and</strong> (j ! , j ! = j ∗ , j ∗ ) are adjoint triples;<br />

(2) j ! , i ∗ <strong>and</strong> j ∗ are fully faithful;<br />

(3) j ∗ i ∗ = 0;<br />

The detailed /final/ versi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> this paper will be /has been/ submitted for publicati<strong>on</strong> elsewhere.<br />

–256–

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