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Exotic Dehn twists on sums of two contact $3$-manifolds

Eduardo Fernández and Juan Muñoz-Echániz

Geometry & Topology 29 (2025) 1571–1618
Abstract

We exhibit the first examples of exotic contactomorphisms with infinite order as elements of the contact mapping class group. These are given by certain Dehn twists on the separating sphere in a connected sum of two closed contact 3-manifolds. We detect these by a combination of hard and soft techniques. We make essential use of an invariant for families of contact structures which generalizes the Kronheimer–Mrowka contact invariant in monopole Floer homology. We then exploit an h-principle for families of convex spheres in tight contact 3-manifolds, from which we establish a parametric version of Colin’s decomposition theorem. As a further application, we exhibit new exotic 1-parametric phenomena in overtwisted contact 3-manifolds.

Keywords
contact structures on 3-manifolds, contactomorphisms, Dehn twist, monopole Floer homology
Mathematical Subject Classification
Primary: 53D35, 57K33, 57R58
References
Publication
Received: 3 July 2023
Revised: 9 April 2024
Accepted: 27 July 2024
Published: 31 May 2025
Proposed: Yakov Eliashberg
Seconded: Ciprian Manolescu, Leonid Polterovich
Authors
Eduardo Fernández
Mathematics Department
University of Georgia
Athens, GA
United States
Juan Muñoz-Echániz
Department of Mathematics
Columbia University
New York, NY
United States
Simons Center for Geometry and Physics
State University of New York, Stony Brook
Stony Brook, NY
United States

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