Ricci flows and bracket flows on twisted principal bundles
We show that Ricci flows of invariant metrics on twisted principal bundles with nilpotent fibres over are immortal and type III. After normalisation and lift to the universal cover, a sequence of metrics converges in the Cheeger–Gromov topology to a homogeneous expanding Ricci soliton. The proof extends the bracket flow technique from homogeneous Ricci flows to invariant Ricci flows on twisted principal bundles.