Jin's conjecture on almost internal logarithmic-differential pullbacks

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Work in a sufficiently saturated differentially closed field U⊨DCF0\mathcal{U}\models\mathrm{DCF}_0 of characteristic zero, with derivation δ\delta, and let F<UF<\mathcal{U} be an algebraically closed differential subfield. Write C\mathcal{C} for the field of constants of FF. Let p∈S1(F)p\in S_1(F) be almost C\mathcal{C}-internal, and let q=log⁡δ−1(p)q=\log_{\delta}^{-1}(p) be its pullback under the logarithmic derivative

log⁡δ(x)=δ(x)x.\log_{\delta}(x)=\frac{\delta(x)}{x}.

Here u⊨qu\models q means that log⁡δ(u)⊨p\log_{\delta}(u)\models p and u∉acl⁡(F,log⁡δ(u))u\notin\operatorname{acl}(F,\log_{\delta}(u)).

Jin's conjecture. The following are equivalent:

  1. qq is almost C\mathcal{C}-internal.
  2. The map log⁡δ:q→p\log_{\delta}:q\to p is almost split.
  3. There is an integer k≠0k\neq 0 such that, for some u⊨qu\models q, there are w1,w2w_1,w_2 satisfying
uuuk=w1w2,u u u^k=w_1w_2,

with w1∈dcl⁡(F,log⁡δ(u))w_1\in\operatorname{dcl}(F,\log_{\delta}(u)) and log⁡δ(w2)∈dcl⁡(F)\log_{\delta}(w_2)\in\operatorname{dcl}(F).

This conjecture characterizes almost C\mathcal{C}-internality of the logarithmic-differential pullback through an almost-splitting condition and an explicit multiplicative decomposition. The source attributes the conjecture to Jin's thesis, but the supplied material gives no resolution status.

References

Primary source

Christine Eagles and Léo Jimenez, “Splitting differential equations using Galois theory”, arXiv:2403.14900 (2025).

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