#### Volume 19, issue 4 (2015)

 Recent Issues
 The Journal About the Journal Subscriptions Editorial Board Editorial Interests Editorial Procedure Submission Guidelines Submission Page Author Index To Appear ISSN (electronic): 1364-0380 ISSN (print): 1465-3060
The invariant measures of some infinite interval exchange maps

### W Patrick Hooper

Geometry & Topology 19 (2015) 1895–2038
##### Abstract

We classify the locally finite ergodic invariant measures of certain infinite interval exchange transformations (IETs). These transformations naturally arise from return maps of the straight-line flow on certain translation surfaces, and the study of the invariant measures for these IETs is equivalent to the study of invariant measures for the straight-line flow in some direction on these translation surfaces. For the surfaces and directions to which our methods apply, we can characterize the locally finite ergodic invariant measures of the straight-line flow in a set of directions of Hausdorff dimension larger than $\frac{\mathfrak{1}}{\mathfrak{2}}$. We promote this characterization to a classification in some cases. For instance, when the surfaces admit a cocompact action by a nilpotent group, we prove each ergodic invariant measure for the straight-line flow is a Maharam measure, and we describe precisely which Maharam measures arise. When the surfaces under consideration are of finite area, the straight-line flows in the directions we understand are uniquely ergodic. Our methods apply to translation surfaces admitting multitwists in a pair of cylinder decompositions in nonparallel directions.

##### Keywords
interval exchange, IET, ergodic, measure classification, Veech group, translation surface, skew product, Maharam measure, infinite ergodic theory, Wind-tree, renormalization
##### Mathematical Subject Classification 2010
Primary: 37E05
Secondary: 37E20, 37A40