The general vv-adic convergence conjecture for Hayes-module exponentials and logarithms

Let ρ\rho be a Hayes module on XX, with no restriction on the genus of XX or on dd_\infty, and let H+H^+ be the field of definition of ρ\rho. Fix a place vv of XX different from \infty, normalized so that the value group is Z\mathbb{Z}. Let KVK_V be the finite field extension of H+H^+ containing all zeros of the Drinfeld divisor VV corresponding to ρ\rho. Fix an embedding KKv\overline K\to\overline K_v, let ww be the place of KVK_V over vv, normalized so that its value group is Z\mathbb{Z}, and let ewe_w be the ramification index of ww over vv.

General vv-adic convergence conjecture. The exponential series eρ(z)e_\rho(z) converges in Cv\mathbb{C}_v whenever

w(z)>w(J0)+eweθ1qdegpfθ1,w(z)>w(J_0)+e_w\cdot e_\theta\cdot\frac{1}{q^{\frac{\deg \mathfrak{p}}{f_\theta}}-1},

where J0J_0 is an ideal depending on the Drinfeld divisor VV evaluated at Ξ\Xi, and eθ,fθe_\theta,f_\theta are positive integers depending respectively on ramification and inertia. The logarithm series logρ(z)\log_\rho(z) converges in Cv\mathbb{C}_v whenever v(z)>0v(z)>0, and the vv-adic valuation of its coefficients has order of magnitude O(n)O(n).

This conjecture extends the convergence results from the genus-zero example to Hayes modules on arbitrary curves and with arbitrary dd_\infty. A principal difficulty is obtaining an explicit integral model for the shtuka function with all zeros integral and expressing the differential ω\omega in terms of that shtuka function.

Sources & referencesView supporting material

Primary source

Kwun Chung, “Factorization of Coefficients for Exponential and Logarithm in Function Fields”, arXiv:2010.12979 (2020).

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