English

Local Factorization of p-adic Gamma Sums

Number Theory 2025-08-13 v1

Abstract

We revisit the proposed equality between discrete Fourier transforms of pp-adic Γp\Gamma_p--values and pp-adic LL--derivatives for odd characters modulo a prime pp. The clean identity is false in general. Building on Coleman reciprocity and the Gross--Koblitz formula, we prove an exact two-term decomposition: for each odd, nontrivial Dirichlet character χ(modp)\chi \pmod p, Φp(χ):=a=1p1χ(a)logpΓp ⁣(ap1)=U1,pLp(0,χ)  +  U2,pL(0,χ), \Phi_p (\chi):=\sum_{a=1}^{p-1}\chi(a)\,\log_p \Gamma_p \!\left(\frac{a}{p-1}\right) = U_{1,p}\,L'_p(0,\chi)\;+\;U_{2,p}\,L(0,\chi), with constants U1,pQp(μp1)×U_{1,p}\in\mathbb{Q}_p(\mu_{p-1})^\times and U2,pQp(μp1)U_{2,p}\in\mathbb{Q}_p(\mu_{p-1}) depending only on pp and the fixed branch of logp\log_p, but independent of χ\chi. Subtracting the L(0,χ)L(0,\chi)--block yields a \emph{renormalized} local input Φpren(χ):=Φp(χ)U2,pL(0,χ)=U1,pLp(0,χ), \Phi^{ren}_p(\chi):=\Phi_p(\chi)-U_{2,p}L(0,\chi)=U_{1,p}\,L'_p(0,\chi), uniformly in odd, nontrivial χ\chi. Plumbing these renormalized locals at every finite place into the Weil explicit formula (with the standard Li kernel at \infty) reproduces exactly the classical Li coefficients. We also record a short, reproducible verification protocol; a tiny table for p=5,7p=5,7 illustrates the χ\chi--independence of (U1,p,U2,p)(U_{1,p},U_{2,p}).

Keywords

Cite

@article{arxiv.2508.08407,
  title  = {Local Factorization of p-adic Gamma Sums},
  author = {Samuel Reid},
  journal= {arXiv preprint arXiv:2508.08407},
  year   = {2025}
}

Comments

5 pages

R2 v1 2026-07-01T04:45:08.072Z