A family of algebraic operations extending the Turaev cobracket

Abstract

We introduce a family of maps parametrised by certain ribbon graphs. It is based on a connection in non-commutative geometry and contains the double divergence as a special case. Applying the construction to the case of the group algebra of the fundamental group of a compact connected oriented surface with boundary, we obtain an algebraic generalisation of the Turaev cobracket. If the connection is flat, they define classes in the Lie algebra cohomology of the space of derivations. In the case of the free associative algebra, we show that they are canonically identified with the standard generators of the cohomology ring of the matrix Lie algebra $\mathfrak{gl}_n$.