Published online by Cambridge University Press: 08 February 2021
For a finite-dimensional Hopf algebra $\mathsf {A}$, the McKay matrix
$\mathsf {M}_{\mathsf {V}}$ of an
$\mathsf {A}$-module
$\mathsf {V}$ encodes the relations for tensoring the simple
$\mathsf {A}$-modules with
$\mathsf {V}$. We prove results about the eigenvalues and the right and left (generalized) eigenvectors of
$\mathsf {M}_{\mathsf {V}}$ by relating them to characters. We show how the projective McKay matrix
$\mathsf {Q}_{\mathsf {V}}$ obtained by tensoring the projective indecomposable modules of
$\mathsf {A}$ with
$\mathsf {V}$ is related to the McKay matrix of the dual module of
$\mathsf {V}$. We illustrate these results for the Drinfeld double
$\mathsf {D}_n$ of the Taft algebra by deriving expressions for the eigenvalues and eigenvectors of
$\mathsf {M}_{\mathsf {V}}$ and
$\mathsf {Q}_{\mathsf {V}}$ in terms of several kinds of Chebyshev polynomials. For the matrix
$\mathsf {N}_{\mathsf {V}}$ that encodes the fusion rules for tensoring
$\mathsf {V}$ with a basis of projective indecomposable
$\mathsf {D}_n$-modules for the image of the Cartan map, we show that the eigenvalues and eigenvectors also have such Chebyshev expressions.