TY - JOUR

T1 - Cross-ratio Dynamics on Ideal Polygons

AU - Arnold, Maxim

AU - Fuchs, Dmitry

AU - Izmestiev, Ivan

AU - Tabachnikov, Serge

N1 - Publisher Copyright:
© 2020 The Author(s) 2018. Published by Oxford University Press. All rights reserved.

PY - 2022/5/1

Y1 - 2022/5/1

N2 - Two ideal polygons, (p1,\ldots, pn) and (q1,\ldots, qn), in the hyperbolic plane or in hyperbolic space are said to be α-related if the cross-ratio [pi,pi+1,qi,qi+1] = α for all i (the vertices lie on the projective line, real or complex, respectively). For example, if α =-1, the respective sides of the two polygons are orthogonal. This relation extends to twisted ideal polygons, that is, polygons with monodromy, and it descends to the moduli space of Möbius-equivalent polygons. We prove that this relation, which is generically a 2-2 map, is completely integrable in the sense of Liouville. We describe integrals and invariant Poisson structures and show that these relations, with different values of the constants α, commute, in an appropriate sense. We investigate the case of small-gons and describe the exceptional ideal pentagons and hexagons that possess infinitely many α-related polygons.

AB - Two ideal polygons, (p1,\ldots, pn) and (q1,\ldots, qn), in the hyperbolic plane or in hyperbolic space are said to be α-related if the cross-ratio [pi,pi+1,qi,qi+1] = α for all i (the vertices lie on the projective line, real or complex, respectively). For example, if α =-1, the respective sides of the two polygons are orthogonal. This relation extends to twisted ideal polygons, that is, polygons with monodromy, and it descends to the moduli space of Möbius-equivalent polygons. We prove that this relation, which is generically a 2-2 map, is completely integrable in the sense of Liouville. We describe integrals and invariant Poisson structures and show that these relations, with different values of the constants α, commute, in an appropriate sense. We investigate the case of small-gons and describe the exceptional ideal pentagons and hexagons that possess infinitely many α-related polygons.

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U2 - 10.1093/imrn/rnaa289

DO - 10.1093/imrn/rnaa289

M3 - Article

AN - SCOPUS:85130026613

SN - 1073-7928

VL - 2022

SP - 6770

EP - 6853

JO - International Mathematics Research Notices

JF - International Mathematics Research Notices

IS - 9

ER -