Modular Invariant Rings and the Weyl Groups of Special Unitary Groups
Kenshi Ishiguro
,
Naito Nishihara
For a compact connected Lie group G, the rational cohomology ring of its classifying space BG can be expressed as an invariant ring. Namely, for a maximal torus $T^{n}$ of G, it is well–known that $H^{*}(BG; \mathbb {Q} ) \cong H^{*}(BT^{n}; \mathbb {Q} )^{W(G)}$ which is a polynomial ring. If d divides n, the quotient $SU(n)/\mathbb {Z}_d$ is also a Lie group. Their rational cohomology rings are isomorphic, however, the integral representations of the Weyl groups $W(SU(n)/\mathbb {Z}_d)$ are not equivalent. So we ask if the modular invariant rings under the actions are polynomial. Our main theorem is a generalization of some results in [4] and [12].