We show that if C is a finite split category, k is a field of characteristic 0 and α is a 2-cocycle of C with values in k × then the twisted category algebra k α C is quasi-hereditary.
IntroductionThroughout this paper we assume that C is a finite category, that is, the objects of C form a finite set, and for every X, Y ∈ Ob(C), the morphism set Hom C (X, Y ) is finite. The category C is called split if, for each morphism s ∈ Hom C (X, Y ), there is a (not necessarily unique) morphism t ∈ Hom C (Y, X) such that s • t • s = s. Note that u := t • s • t then also satisfies s • u • s = s, and also u • s • u = u. In the special case where C has only one object this leads to the notion of a regular monoid, see [10].Let k be a field, and let α be a 2-cocycle of C with values in k × . That is, for every pair s, t ∈ Mor(C) such that t •s exists, one has an element α(t, s) ∈ k × such that the following holds: for any s, t, u ∈ Mor(C) such that t • s and u • t exist, one has α(u • t, s)α(u, t) = α(u, t • s)α(t, s). We will study the twisted category algebra k α C, that is, the k-vector space with basis Mor(C) and multiplicationThe aim of this paper, see Theorem 3.5, is to show that if C is a finite split category and if k has characteristic 0 then k α C is a quasi-hereditary algebra. This generalizes a result of Putcha, see [16], who proved that regular monoid algebras are quasi-hereditary over k = C. In Theorem 4.2 we identify the standard modules, generalizing Putcha's results in [16].