Jin's conjecture on almost internal logarithmic-differential pullbacks

From papers

Work in a sufficiently saturated differentially closed field UDCF0\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 pS1(F)p\in S_1(F) be almost C\mathcal{C}-internal, and let q=logδ1(p)q=\log_{\delta}^{-1}(p) be its pullback under the logarithmic derivative

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

Here uqu\models q means that logδ(u)p\log_{\delta}(u)\models p and uacl(F,logδ(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 logδ:qp\log_{\delta}:q\to p is almost split.
  3. There is an integer k0k\neq 0 such that, for some uqu\models q, there are w1,w2w_1,w_2 satisfying
uuuk=w1w2,u u u^k=w_1w_2,

with w1dcl(F,logδ(u))w_1\in\operatorname{dcl}(F,\log_{\delta}(u)) and logδ(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.

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Sources & referencesView supporting material

Primary source

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

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