Invariant Random Subgroups and Metrics on Moduli Spaces of Riemann Surfaces

Invariant Random Subgroups and Metrics on Moduli Spaces of Riemann Surfaces

Invariant Random Subgroups and Metrics on Moduli Spaces of Riemann Surfaces

Thursday, July 23, 2026
  • Lecturer: Polina Leonchik (Technion)
  • Location: Amado 919
Abstract:
An invariant random subgroup is a conjugation-invariant probability measure on the space of closed subgroups of a given group. Such measures may be viewed as a common generalization of normal subgroups and lattices.
Every finite-area hyperbolic surface determines an invariant random subgroup of the group of orientation-preserving isometries of the hyperbolic plane. In this way, the moduli space of the surface embeds into the space of invariant random subgroups. Taking the closure of its image produces a compactification known as the IRS compactification. Krifka proved that there is a continuous finite-to-one map from the augmented moduli space onto this compactification.
The main goal of the talk is to construct metrics on the moduli space of the once-punctured torus using the invariant-random-subgroup approach. We will then discuss their behaviour when a simple closed geodesic is pinched and compare the resulting asymptotic estimates with those for the classical Weil--Petersson metric.
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