Group action on Sylow subgroups

823 Views Asked by At

Let $G$ be a finite group, $p$ a prime dividing the order of $G$, $X$ the set of $p$-Sylow subgroups of $G$. $G$ acts on $X$ by conjugation, and by the Sylow theorems the action is transitive and $\lvert X \rvert \equiv 1\pmod p$. Can we say anything more about the action? An answer to any single one of the following questions would be very welcome.

  1. If the action is imprimitive, so the normalizers are not maximal, what do the blocks of imprimitivity look like?

  2. If it is primitive, when is it $2$-transitive? $k$-transitive?

  3. Is the action always faithful? How do two normalizers (point stabilizers) intersect?

  4. What does the action of the normalizer $G_x$ on $X \, \backslash \, \{ x \}$ look like? What about the action of the $p$-Sylow alone?

  5. We can also look at the action of a subgroup $H \leq G$ on $X$: when is it transitive? Otherwise, what do the orbits look like?

  6. What can we say about a subgroup $H \leq G$ that acts regularly on $X$?

I know that's a lot of questions, but I'm just trying to get a better grasp of the action of $G$ on $X$, because I didn't find much more than transitivity itself in the litterature. Thanks in advance!