Jossen's conjecture on division and common zeros of E-functions

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An EE-function is a power series f(x)=∑n=0∞anxn/n!∈Q‾[[x]]f(x)=\sum_{n=0}^{\infty}a_nx^n/n!\in\overline{\mathbb Q}[[x]] satisfying the three defining growth, integrality, and differential-equation conditions. A unit is an EE-function of the form αeβx\alpha e^{\beta x} with α,β∈Q‾\alpha,\beta\in\overline{\mathbb Q} and α≠0\alpha\neq0.

Jossen's conjecture. (i) If ff and gg are two EE-functions such that f/gf/g is entire, then f/gf/g is an EE-function. (ii) If two EE-functions ff and gg share at least one common root, then there exists a non-unit EE-function hh such that f/hf/h and g/hg/h are EE-functions.

Part (i) is known for exponential polynomials over Q‾\overline{\mathbb Q} and when gg is a polynomial; part (ii) is known when the common root is algebraic. The general conjecture remains open.

References

Primary source

Stéphane Fischler and Tanguy Rivoal, “Zeros of E-functions and of exponential polynomials defined over Q”, arXiv:2503.20345 (2025).

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