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Consider the manifold $M := \operatorname{SO}(n) \times \mathbb{S}^{n-1}$, endowed with the product metric given by the bi-invariant metric of $\operatorname{SO}(n)$ and the round metric of $\mathbb{S}^{n-1}$.

Consider the left action of $\operatorname{SO}(m)$, for some $m \leq n$ on $M$ given as $(g, (x, y)) \mapsto (xg^t, gy)$ for every $g \in \operatorname{SO}(m)$ and every $(x, y) \in \operatorname{SO}(n) \times \mathbb{S}^{n-1}$. Seeing $\operatorname{SO}(m)$ as a subgroup of $\operatorname{SO}(n)$ of the form $$ \begin{pmatrix} I_{n-m} & 0\\ 0 & U \end{pmatrix}, $$ with $I_{n-m}$ the identity matrix of dimension $n-m$ and $U \in \operatorname{SO}(m)$.

Since the action is free, smooth and proper, there exists a metric on $M/\operatorname{SO}(m)$ such that the map $\pi: M \to M/\operatorname{SO}(m)$ is a Riemannian submersion with totally geodesic fibres.

From O'Neill's formula, we know that for every pair of orthonormal horizontal vectors $U, W \in T_{(x,y)} M$, $$ K_{M/\operatorname{SO}(m)}(\pi_* U, \pi_* W) = K_M(U, W) + \frac{3}{4}|[U, W]^V|^2, $$ where $K_{M/\operatorname{SO}(m)}$ is the sectional curvature of $M/\operatorname{SO}(m)$, $K_M$ is the sectional curvature of $M$, and $[U, W]^V$ is the vertical component of the Lie derivative of $U$ and $W$. (Note that the latter is well-defined since for every two horizontal vector fields $\tilde{U}$, $\tilde{W}$ extending $U, W$, the vertical component of their Lie derivative $[\tilde{U}, \tilde{W}]^V$ only depends on $U$ and $W$).

My question is: is it possible to upper bound $|[U, W]^V|^2$? This way, it would be possible to upper bound the curvature of the quotient space.

Update: I am not sure if it would be helpful to see $\mathbb{S}^{n-1}$ as the quotient $\operatorname{SO}(n)/\operatorname{SO}(n-1)$, that way one can see the total space $M$ as a Lie group ($\operatorname{SO}(n) \times \operatorname{SO}(n)$) endowed with the bi-invariant metric. Modifying the action accordingly, which now would be given by the group $\operatorname{SO}(m) \times \operatorname{SO}(n-1)$, as $$ ((g, h), (x, y)) \mapsto (xg^t, gyh), $$ for any $(g, h) \in \operatorname{SO}(m) \times \operatorname{SO}(n-1)$, and any $(x, y) \in \operatorname{SO}(n) \times \operatorname{SO}(n)$. In this setting, I believe the quotient space is a bi-quotient (see @RamiroLafuente 's comment). Does this make things any simpler or clearer?

Clarification: I know there exists a bound from the fact that the quotient space is compact, but I need something explicit. At least I would need how the curvature grows (linearly, polynomially, exponentially...) with respect to the dimensions of the original manifold and the group acting on it.

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    $\begingroup$ This manifold is a biquotient, as you noted in your Update at the end of the post. The sectional curvature of biquotients has been studied thoroughly in the literature for various examples, due to their connection to positive curvature. See e.g. link.springer.com/article/10.1007/s00208-011-0634-7 (arXiv version arxiv.org/pdf/0809.4771) and therein references, which may help with your bounds. $\endgroup$ Commented Jul 5 at 4:06
  • $\begingroup$ Thank you for your comment @RamiroLafuente ! I see that Eschenburg habilitation seems to be a good reference text. Unluckily, it is only written in German. Do you know any other good references to get started on this topic? $\endgroup$ Commented Jul 5 at 11:06
  • $\begingroup$ From compactness, there is an upper bound. It might be tricky to find an exact bound, but maybe you do not need it. $\endgroup$ Commented Jul 12 at 3:17
  • $\begingroup$ Thanks, @AntonPetrunin but yeah I need a more explicit bound (I need to see at least its relation with the dimension of the manifold) $\endgroup$ Commented Jul 12 at 8:13
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    $\begingroup$ Please be aware that the software has flagged this question as having more than 20 edits. In the span of 5 weeks that is rather a lot, and each edit bumps the question to the top of the front page. A lot of these edits were exceedingly minor (adding one comma to a displayed equation??) This behaviour is looked down, it is better to really ensure that edits are saved up and done all at once, or else minor stylistic edits can be foregone. $\endgroup$
    – David Roberts
    Commented Aug 7 at 1:34

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