Journal Home Page Cumulative Index List of all Volumes Complete Contentsof this Volume Previous Article Journal of Lie Theory 31 (2021), No. 4, 1085--1112Copyright Heldermann Verlag 2021 A Calabi-Yau Algebra with E6 Symmetry and the Clebsch-Gordan Series of sl(3) Nicolas Crampé Institut Denis-Poisson, Université de Tours et d'Orléans, Tours, France crampe1977@gmail.com Loic Poulain d'Andecy Laboratoire de Mathématiques, Université de Reims-Champagne-Ardenne, Reims, France loic.poulain-dandecy@univ-reims.fr Luc Vinet Centre de Recherches Mathématiques, Université de Montrél, Canada vinet@crm.umontreal.ca [Abstract-pdf] Building on classical invariant theory, it is observed that the polarised traces generate the centraliser $Z_L(sl(N))$ of the diagonal embedding of $U(sl(N))$ in $U(sl(N))^{\otimes L}$. The paper then focuses on $sl(3)$ and the case $L=2$. A Calabi-Yau algebra $\mathcal{A}$ with three generators is introduced and explicitly shown to possess a PBW basis and a certain central element. It is seen that $Z_2(sl(3))$ is isomorphic to a quotient of the algebra $\mathcal{A}$ by a single explicit relation fixing the value of the central element. Upon concentrating on three highest weight representations occurring in the Clebsch-Gordan series of $U(sl(3))$, a specialisation of $\mathcal{A}$ arises, involving the pairs of numbers characterising the three highest weights. In this realisation in $U(sl(3))\otimes U(sl(3))$, the coefficients in the defining relations and the value of the central element have degrees that correspond to the fundamental degrees of the Weyl group of type $E_6$. With the correct association between the six parameters of the representations and some roots of $E_6$, the symmetry under the full Weyl group of type $E_6$ is made manifest. The coefficients of the relations and the value of the central element in the realisation in $U(sl(3))\otimes U(sl(3))$ are expressed in terms of the fundamental invariant polynomials associated to $E_6$. It is also shown that the relations of the algebra $\mathcal{A}$ can be realised with Heun type operators in the Racah or Hahn algebra. Keywords: Calabi-Yau algebra, polarised traces, centraliser algebra, Clebsch-Gordan series, Heun operators, Weyl group of type E6. MSC: 17B35, 16S30, 17B10, 16R30, 22E46. [ Fulltext-pdf  (218  KB)] for subscribers only.