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On the critical regularity of nilpotent groups acting on the interval: the metabelian case
- Part of
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- Journal:
- Ergodic Theory and Dynamical Systems , First View
- Published online by Cambridge University Press:
- 24 September 2024, pp. 1-22
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Let G be a torsion-free, finitely generated, nilpotent and metabelian group. In this work, we show that G embeds into the group of orientation-preserving
$C^{1+\alpha }$-diffeomorphisms of the compact interval for all 
$\alpha < 1/k$, where k is the torsion-free rank of 
$G/A$ and A is a maximal abelian subgroup. We show that, in many situations, the corresponding 
$1/k$ is critical in the sense that there is no embedding of G with higher regularity. A particularly nice family where this happens is the family of 
$(2n+1)$-dimensional Heisenberg groups, for which we can show that the critical regularity is equal to 
$1+1/n$.
