Chekanov’s Lagrangian Hofer Metric

Updated 5 August 2025

Chekanov's Lagrangian Hofer metric is a quantitative invariant that measures the minimal Hofer energy required to connect Hamiltonian isotopic Lagrangian submanifolds.
It leverages Floer theory and J-holomorphic curve techniques to establish nondegeneracy and derive explicit lower bounds through spectral invariants.
The metric reveals rich large-scale geometry via quasi-isometric embeddings, demonstrating features like infinite diameter and structural rigidity in Lagrangian spaces.

Chekanov’s Lagrangian Hofer metric is a fundamental quantitative invariant in symplectic topology that measures the minimal Hofer energy required to connect Hamiltonian isotopic Lagrangian submanifolds. Analogous to Hofer’s metric on the Hamiltonian diffeomorphism group, Chekanov’s metric establishes a rich metric structure on the space of Lagrangians Hamiltonian isotopic to a given submanifold, playing a central role in the interface between symplectic dynamics, holomorphic curve theory, and Floer-theoretic invariants.

1. Definition and Core Properties

Let $(M,\omega)$ be a symplectic manifold and $L\subset M$ a closed, connected Lagrangian submanifold. Chekanov’s Lagrangian Hofer metric $d_{LH}$ is defined on the orbit

$\mathcal{L}(L) = \{\varphi(L) \mid \varphi \in \text{Ham}(M, \omega)\}$

$d_{LH}(L', L'') = \inf \{ \|\varphi\| \mid \varphi \in \text{Ham}(M, \omega),\ \varphi(L') = L'' \}$

where the Hofer norm is

$\|\varphi\| = \inf_{\varphi = \varphi_H^1} \int_0^1 \left( \max_M H_t - \min_M H_t \right) dt$

with $H$ any time-dependent Hamiltonian generating $\varphi$ .

In this context, $d_{LH}$ quantifies the ‘energy cost’ of moving from one Lagrangian to another in its Hamiltonian orbit. The metric is nondegenerate for Lagrangian submanifolds under mild assumptions: for monotone or exact Lagrangians, Chekanov’s original theorem, and subsequent refinements, guarantee nondegeneracy, meaning $d_{LH}(L, L') > 0$ whenever $L\neq L'$ are Hamiltonian isotopic (Charette, 2010).

A central result refined Chekanov’s metric nondegeneracy by connecting it to $J$ -holomorphic curve theory. Specifically, if $L,L'$ are monotone, Hamiltonian isotopic Lagrangian submanifolds, and $r$ is the radius of a symplectic ball disjoint from $L'$ whose real part lies in $L$ , then

$(\pi/2)\, r^2 \leq d_{LH}(L,L')$

and, crucially, there exists a nonconstant $J$ -holomorphic curve (strip, disk, or sphere) passing through prescribed points with symplectic area bounded above by $d_{LH}(L,L')$ . In many scenarios, the Maslov index of this curve can also be controlled, connecting the metric with algebraic invariants from Floer theory (Charette, 2010). This geometric refinement ensures that not only is the distance nonzero, but it is ‘witnessed’ by holomorphic curve data, providing explicit lower bounds for displacement energy and directly relating Hofer metrics to holomorphic curve theory.

3. Spectral Invariants and Metric Computation

Floer-theoretic spectral invariants are integral to metric computations and lower bounds. Given a Hamiltonian $H$ and an intersection point or chord $\gamma$ , the action functional is

$\mathcal{A}_H^L(\gamma) = \int_0^1 H_t(\gamma(t))\, dt - \int_{D^+} u^*\omega$

where $u$ contracts $\gamma$ to $L$ (Zapolsky, 2012). Spectral invariants associated to Floer homology classes satisfy

$\int_0^1 \min_{M}(H_t - G_t) dt \leq \ell(\alpha, H:L,L') - \ell(\alpha, G:L,L') \leq \int_0^1 \max_{M}(H_t - G_t) dt$

and provide lower bounds for the Lagrangian Hofer metric. Applying this theory, one can describe explicit isometric (or quasi-isometric) embeddings

$\mathbb{R}^k \to (\mathcal{L}(L), d_{LH}),\;\; \tau \mapsto L_\tau$

with

$d_{LH}(L_0, L_\tau) = \text{osc}_0(\tau) := \max_{i,j} |\tau_i - \tau_j|$

for certain controlled configurations of Lagrangians and Hamiltonians (Zapolsky, 2012). This framework allows explicit computation of the metric in various aspherical settings and demonstrates the “size” of the orbit space.

4. Large-Scale Geometry: Unboundedness and Quasi-Isometric Embeddings

The metric space $(\mathcal{L}(L), d_{LH})$ often exhibits large-scale, noncompact geometry. It is established for many classes of Lagrangians—the Clifford torus in complex projective space and the four-dimensional quadric, product tori in bidisks, cotangent fibers, A₃-configurations of spheres—that there exist quasi-isometric (even isometric) embeddings of normed linear spaces (such as $(\mathbb{R}, |\cdot|)$ , $(\mathbb{R}^\infty, \|\cdot\|_\infty)$ , or even function spaces) into $(\mathcal{L}(L), d_{LH})$ (Zapolsky, 4 Aug 2025, Usher, 2013, Dawid, 26 Feb 2024, Masatani, 2015): $A\|v-w\| - D \leq d_{LH}(L_v, L_w) \leq B\|v-w\|$ for constants $A, B, D > 0$ . For the Clifford torus $T$ , in projective space,

$\frac{1}{2}|s-t| - D \leq d_{LH}(L_s, L_t) \leq |s-t|$

for a suitable family of Lagrangians $(L_t)_{t\in\mathbb{R}}$ (Zapolsky, 4 Aug 2025). This implies that $(\mathcal{L}(L), d_{LH})$ can have infinite diameter, admitting infinitely long “lines” in the metric geometry—quantitative evidence of the richness of Hamiltonian deformation spaces.

The mechanism for these embeddings often relies on explicit spectral invariants and, importantly, on the Lipschitz or quasi-morphism property of functions constructed via Floer theory or toric degenerations (Kawamoto, 2022).

5. Persistence, Boundary Depth, and Floer Homology

Beyond the basic spectral invariant, finer invariants such as Floer barcode lengths, boundary depth, and persistent Floer homology give robust bounds and structure for the metric. One obtains upper bounds in terms of barcode data: $d_H(L_0, L) \leq \sum_{j=1}^{n-1} 2^j \beta_j(L_0, L) + \gamma(L_0, L)$ where the $\beta_j$ are barcode bar lengths and $\gamma$ is a spectral gap (Dietzsch, 2023). Boundary depth serves as a 1-Lipschitz function with respect to the metric, and unboundedness of boundary depth translates directly to unbounded metric diameter (Usher, 2013, Dawid, 26 Feb 2024).

In sectors with rich Floer theory, notably for cotangent fibers in disk cotangent bundles and in A₃-configurations, wrapped Floer cohomology’s nonvanishing forces the Hofer metric to be unbounded (Gong, 2023, Dawid, 26 Feb 2024). Conversely, vanishing of wrapped Floer cohomology corresponds to potentially finite diameter.

6. Topological and Metric Constraints

In families of Lagrangians controlled by uniform Riemannian bounds (such as those with bounded second fundamental form and tameness), the geometry induced by the Hofer metric is especially rigid—there are only finitely many Hamiltonian isotopy classes within any such bounded family, with each non-isotopic pair separated by a definite, strictly positive distance (Chassé, 29 May 2024). In such spaces, metric completions are compact and pathologies such as Ostrover’s “boundaries” are ruled out.

When the metric is combined with geometric bounds, as in the case of graphs of exact 1-forms in cotangent bundles, explicit formulas apply: $d_H(\text{graph}\,df, \text{graph}\,dg) = \max |f-g| - \min |f-g|$ giving a concrete realization of the metric structure (Chassé, 29 May 2024).

7. Quantitative and Qualitative Rigidity

Chekanov’s metric provides a robust link between symplectic and Riemannian geometries. For instance, a Hölder-type inequality relates the Hausdorff distance (in Riemannian terms) and the Lagrangian spectral (or Hofer) metric: $\delta_H(L, L') \leq C\sqrt{\gamma(L,L')}\|d\psi\|$ where $C$ depends on ambient and submanifold metric data, and $\psi$ realizes the isotopy (Chassé et al., 2023). This demonstrates how symplectic “energy” controls geometric “distance.”

Lower semicontinuity phenomena further underscore rigidity: the Lagrangian volume, with respect to the Hofer metric, is lower semicontinuous—small energy perturbations cannot abruptly decrease volume (Cineli et al., 2022). This reflects deeper structural stability for monotone and symmetric Lagrangian settings.

8. Contact Analogues and Degeneracy Dichotomy

A direct contact analogue exists: in contact manifolds, the Shelukhin–Chekanov–Hofer pseudo-metric mirrors Chekanov’s original dichotomy. For submanifolds of Legendrian dimension $n$ , the Shelukhin–Chekanov–Hofer pseudo-metric exhibits a dichotomy: it is either genuinely nondegenerate or vanishes identically, a phenomenon closely paralleling Chekanov’s metric for Lagrangians (Rosen et al., 2018, Nakamura, 2023). This dichotomy provides both obstructions and confirmations of rigidity in both categories.

Conclusion

Chekanov’s Lagrangian Hofer metric establishes a rigorous metric geometry on the space of Hamiltonian deformations of Lagrangian submanifolds, with rich connections to Floer theory, holomorphic curve techniques, and symplectic rigidity phenomena. It supports explicit quasi-isometric embeddings, infinite-dimensional quasi-flats, and is intimately related to spectral invariants, boundary depth, and persistence. The metric’s responses to Riemannian and symplectic constraints not only rule out certain pathological phenomena but also provide quantifiable links between symplectic and Riemannian geometries. The dichotomy property and extensions to contact topology highlight its deep role in determining the structure and rigidity of Lagrangian and Legendrian objects in both local and large-scale symplectic topology.