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Apr 10, 2017 at 18:31 comment added Llohann You can use the compact version $SO(4)/S(O(2)\times O(2))$ (or something like that). people.sju.edu/~ktapp/so4.pdf gives a nice account on left-invariant metrics on $SO(4)$. On the other hand, I am pretty sure that homogeneous manifolds with positive curvature are already classified (please look at Ziller or Wilking survey on positively curved manifolds).
Apr 10, 2017 at 18:14 comment added L.F. Cavenaghi Nice! Do you know any article that provides the search for $G$-invariants metrics in this space?
Apr 10, 2017 at 18:07 comment added Bombyx mori @MikhailBorovoi: See math.stackexchange.com/questions/1828484/…, for example. You might find Qiaochu's answer easier to read than mine: math.stackexchange.com/questions/219100/…
Apr 10, 2017 at 16:37 comment added Mikhail Borovoi Could you please explain here how you construct a bijection between $S^2\times S^2$ and the set of oriented 2-planes in $\mathbb R^4$ ?
Apr 10, 2017 at 16:00 comment added Ben McKay But the maximal compact subgroup is $PSO(4)=SO(3) \times SO(3)$, preserving the splitting, if I remember correctly.
Apr 10, 2017 at 15:55 comment added Ben McKay See arxiv.org/pdf/math/0101017.pdf p. 5 for details.
Apr 10, 2017 at 15:53 history answered Ben McKay CC BY-SA 3.0