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Invariant random subgroups of semidirect products. (English) Zbl 1437.37002

The authors study transverse invariant random subgroups (IRSs) of semidirect products \(G=A \rtimes \Gamma\) when \(A\) is torsion-free abelian or simply connected nilpotent.
In particular, they characterize all IRSs of parabolic subgroups of \(\mathrm{SL}_d(\mathbb {R})\), and show that all ergodic IRSs of \(\mathbb {R}^d \rtimes \mathrm{SL}_d(\mathbb {R})\) are either of the form \(\mathbb {R}^d \rtimes K\) for some IRS of \(\mathrm{SL}_d(\mathbb {R})\), or are induced from IRSs of \(\Lambda \rtimes \mathrm{SL}(\Lambda)\), where \(\Lambda < \mathbb {R}^d\) is a lattice.
As applications they study IRSs of two familiar semidirect products: the special affine groups \(\mathbb {R}^d \rtimes \mathrm{SL}_d(\mathbb {R})\) and the parabolic subgroups of \(\mathrm{SL}_d(\mathbb {R})\).

MSC:

37A15 General groups of measure-preserving transformations and dynamical systems
37A05 Dynamical aspects of measure-preserving transformations
37A20 Algebraic ergodic theory, cocycles, orbit equivalence, ergodic equivalence relations
22E40 Discrete subgroups of Lie groups
22D40 Ergodic theory on groups

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