Lusternik-Schnirelmann categories of non-simply connected compact simple Lie groups

Abstract

Let $F\hookrightarrow X\to B$ be a fibre bundle with structure group $G$, where $B$ is $(d-1)$-connected and of finite dimension, $d\ge 1$. We prove that the strong L-S category of $X$ is less than or equal to $m+\frac{\dim B}{d}$, if $F$ has a cone decomposition of length $m$ under a compatibility condition with the action of $G$ on $F$. This gives a consistent prospect to determine the L-S category of non-simply connected Lie groups. For example, we obtain $\cat{PU(n)} \leq 3(n{-}1)$ for all $n\ge 1$, which might be best possible, since we have $\cat{\mathrm{PU}(p^r)}=3(p^r{-}1)$ for any prime $p$ and $r\ge 1$. Similarly, we obtain the L-S category of $\mathrm{SO}(n)$ for $n\le 9$ and $\mathrm{PO}(8)$. We remark that all the above Lie groups satisfy the Ganea conjecture on L-S category.

13 pages