Crofton-type conjecture for random Hamiltonian diffeomorphisms

Let (M,ω)(M,\omega) be a closed symplectic manifold and let D\mathcal{D} be a centered, time-symmetric, exhaustive or periodically exhaustive law-defining datum. Let LML\subset M be a closed Lagrangian submanifold. The datum specifies an almost complex structure JJ and the associated Riemannian metric gg.

Crofton-type conjecture. There exist a constant C>0C>0 and a smooth function ρ:MR>0\rho:M\to\mathbb{R}_{>0}, depending only on D\mathcal{D} and LL and satisfying

Mρωn=vol(M),\int_M \rho\,\omega^n=\operatorname{vol}(M),

such that, for every closed Lagrangian submanifold KMK\subset M,

Ham(M,ω)#(Lφ(K))dμHamD(φ)=Cvolρg(K).\int_{\operatorname{Ham}(M,\omega)} \#(L\cap\varphi(K))\,d\mu_{\operatorname{Ham}}^{\mathcal{D}}(\varphi)=C\cdot\operatorname{vol}_{\rho\cdot g}(K).

In particular, there exist constants C,C>0C',C”>0 such that

Cvolg(K)Ham(M,ω)#(Lφ(K))dμHamD(φ)Cvolg(K).C'\cdot\operatorname{vol}_g(K)\leq\int_{\operatorname{Ham}(M,\omega)}\#(L\cap\varphi(K))\,d\mu_{\operatorname{Ham}}^{\mathcal{D}}(\varphi)\leq C”\cdot\operatorname{vol}_g(K).

The conjecture seeks a Crofton formula for expected Lagrangian intersection counts, with a density-rescaled metric accounting for the nonuniform behavior seen in simulations. The supplied text gives numerical evidence and explains why the standard metric does not yield an exact formula, but states no resolution; the conjecture remains open.

Sources & referencesView supporting material

Primary source

Adrian Dawid, “Random Hamiltonians I: Probability measures and random walks on the Hamiltonian diffeomorphism group”, arXiv:2510.03190 (2025).

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