Rationality of the Exceptional $\mathcal {W}$-Algebras $\mathcal {W}_k(\mathfrak {sp}_{4},f_{subreg})$ Associated with Subregular Nilpotent Elements of $\mathfrak {sp}_{4}$
Résumé
We prove the rationality of the exceptional $\mathcal {W}$-algebras $\mathcal {W}_k(\mathfrak {g},f)$ associated with the simple Lie algebra $\mathfrak {g}=\mathfrak {sp}_{4}$ and a subregular nilpotent element $f=f_{subreg}$ of $\mathfrak {sp}_{4}$, proving a new particular case of a conjecture of Kac–Wakimoto. Moreover, we describe the simple $\mathcal {W}_k(\mathfrak {g},f)$-modules and compute their characters. We also work out the nontrivial action of the component group on the set of simple $\mathcal {W}_k(\mathfrak {g},f)$-modules.