CR-invariant energy of Legendrian knots in the Heisenberg group

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Autori principali: Matsumoto, Yoshihiko, O'Hara, Jun
Natura: Preprint
Pubblicazione: 2026
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author Matsumoto, Yoshihiko
O'Hara, Jun
author_facet Matsumoto, Yoshihiko
O'Hara, Jun
contents We introduce an energy functional for Legendrian knots in the 3-dimensional Heisenberg group $\mathcal{H}$, which serves as a sub-Riemannian analog of the Möbius invariant knot energy in Euclidean 3-space introduced by the second author. The energy is obtained by regularizing a divergent integral of the potential of order -2 with respect to the Korányi distance on $\mathcal{H}$; this choice of distance is essential for the energy to be invariant under the action of PU(2,1). We characterize $\mathbb{R}$-circles in $\mathcal{H}$ as the minimizers of the energy, and establish a Heisenberg analog of the Doyle--Schramm cosine formula. We also show that the energy integrand admits an expression in terms of a complex-valued 2-form on the complement of the diagonal in $\mathcal{H}\times\mathcal{H}$, providing a partial analog of the infinitesimal cross ratio interpretation known from the classical setting.
format Preprint
id arxiv_https___arxiv_org_abs_2604_25713
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle CR-invariant energy of Legendrian knots in the Heisenberg group
Matsumoto, Yoshihiko
O'Hara, Jun
Geometric Topology
Complex Variables
Differential Geometry
57K10 (Primary) 32V05, 57K33 (Secondary)
We introduce an energy functional for Legendrian knots in the 3-dimensional Heisenberg group $\mathcal{H}$, which serves as a sub-Riemannian analog of the Möbius invariant knot energy in Euclidean 3-space introduced by the second author. The energy is obtained by regularizing a divergent integral of the potential of order -2 with respect to the Korányi distance on $\mathcal{H}$; this choice of distance is essential for the energy to be invariant under the action of PU(2,1). We characterize $\mathbb{R}$-circles in $\mathcal{H}$ as the minimizers of the energy, and establish a Heisenberg analog of the Doyle--Schramm cosine formula. We also show that the energy integrand admits an expression in terms of a complex-valued 2-form on the complement of the diagonal in $\mathcal{H}\times\mathcal{H}$, providing a partial analog of the infinitesimal cross ratio interpretation known from the classical setting.
title CR-invariant energy of Legendrian knots in the Heisenberg group
topic Geometric Topology
Complex Variables
Differential Geometry
57K10 (Primary) 32V05, 57K33 (Secondary)
url https://arxiv.org/abs/2604.25713