Let $G$ be a finite dimensional connected Lie group and $Diffeo(G)$ be the diffeomorphism group of the underlying manifold. Is it true that $Diffeo(G)$ has the homotopy type of a finite dimensional Lie group? I can't seem to find a counterexample.
2026-04-01 14:02:53.1775052173
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Homotopy Type of Diffeomorphism Group of Lie Group
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A lower dimensional example is $S^1\times S^2$.
Hatcher calculated the homotopy type of $Diff(S^1\times S^2)$: It is the one of $O(2)\times O(3)\times \Omega SO(3)$. As the second homotopy group of this space does not vanish since $\pi_2(O(2)\times O(3)\times \Omega SO(3))\cong \mathbb{Z}$ holds, it cannot have the homotopy type of a finite dimensional Lie group.
Torus of dimension $\ge 25$ is a counter example. See here.