Let G be a group acting on ℝ2 by orientation-preserving homeomorphisms. We show that a tight bound on orbits implies a global fixed point. Precisely, if for some k > 0 there is a ball of radius r > (1∕3)k such that each point x in the ball satisfies ∥g(x) − h(x)∥≤ k for all g,h ∈ G, and the action of G satisfies a nonwandering hypothesis, then the action has a global fixed point. In particular any group of measure-preserving, orientation-preserving homeomorphisms of ℝ2 with uniformly bounded orbits has a global fixed point. The constant (1∕3)k is sharp.
As an application, we also show that a group acting on ℝ2 by diffeomorphisms with orbits bounded as above is left orderable.
Keywords: fixed point, planar action, group action, prime end, left order, plane homeomorphism, Brouwer plane translation
Mann, Kathryn  1
@article{10_2140_agt_2012_12_421,
author = {Mann, Kathryn},
title = {Bounded orbits and global fixed points for groups acting on the plane},
journal = {Algebraic and Geometric Topology},
pages = {421--433},
year = {2012},
volume = {12},
number = {1},
doi = {10.2140/agt.2012.12.421},
url = {http://geodesic.mathdoc.fr/articles/10.2140/agt.2012.12.421/}
}
TY - JOUR AU - Mann, Kathryn TI - Bounded orbits and global fixed points for groups acting on the plane JO - Algebraic and Geometric Topology PY - 2012 SP - 421 EP - 433 VL - 12 IS - 1 UR - http://geodesic.mathdoc.fr/articles/10.2140/agt.2012.12.421/ DO - 10.2140/agt.2012.12.421 ID - 10_2140_agt_2012_12_421 ER -
Mann, Kathryn. Bounded orbits and global fixed points for groups acting on the plane. Algebraic and Geometric Topology, Tome 12 (2012) no. 1, pp. 421-433. doi: 10.2140/agt.2012.12.421
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