Extensions between functors from Jacobi diagrams in handlebodies

Abstract: The first Ext-groups between Schur functors in the category of modules over the $\Bbbk$-linearization $\Bbbk\mathbf{gr}^{\operatorname{op}}$ of the opposite of the category of finitely generated free groups are computed for a filed $\Bbbk$ of characteristic $0$. The $\Bbbk$-linear category $\mathbf{A}$ of Jacobi diagrams in handlebodies, which was introduced by Habiro and Massuyeau, has an $\mathbb{N}$-grading whose degree $0$ part identifies with the category $\Bbbk\mathbf{gr}^{\operatorname{op}}$. We compute the first Ext-groups in the category of $\mathbf{A}$-modules between simple $\mathbf{A}$-modules which are induced by Schur functors.