ON MAXIMAL DIAGONALIZABLE LIE SUBALGEBRAS OF THE FIRST HOCHSCHILD COHOMOLOGY

Let A be a basic connected finite dimensional algebra over an algebraically closed field, with ordinary quiver without oriented cycles. Given a presentation of A by quiver and admissible relations, Assem and de la Pena have constructed an embedding of the space of additive characters of the fundamental group of the presentation into the first Hochschild cohomology group of A. We compare the embeddings given by the different presentations of A. In some situations, we characterise the images of these embeddings in terms of ( maximal) diagonalizable subalgebras of the first Hochschild cohomology group ( endowed with its Lie algebra structure).