English

A partial dictionary between universal central extensions and orthogonal polynomials in the superelliptic Krichever--Novikov setting

Representation Theory 2026-05-05 v1

Abstract

Let m2m \geq 2, let P(x)C[x]P(x) \in \mathbb{C}[x] have simple roots, and let A=C[x±1,uum=P(x)]A = \mathbb{C}[x^{\pm 1},\,u \mid u^m = P(x)] be the coordinate ring of the associated superelliptic curve. The derivation algebra Der(A)\mathrm{Der}(A) and the current algebra gA\mathfrak{g}\otimes A (for g\mathfrak{g} a simple Lie algebra) each admit a universal central extension whose center is multi-dimensional and carries linear algebraic relations among its basis elements. We establish a systematic dictionary between these relations and families of orthogonal polynomials in the parameter aa encoding the branch locus of PP. The dictionary has three canonical entries: (1)~the basis reduction relations in the center of Der(A)^\widehat{\mathrm{Der}(A)} are exactly the three-term recurrence of an orthogonal polynomial family; (2)~the generating function of the center satisfies the Sturm--Liouville ODE of that family; (3)~the mixed-sector 22-cocycle equals the Legendre antiderivative (Pn1(a)Pn+1(a))/(2n+1)(P_{n-1}(a)-P_{n+1}(a))/(2n+1) in the quadratic case. We prove the dictionary completely for P(x)=x22ax+1P(x)=x^2-2ax+1 (Legendre polynomials) and for the quartic palindromic case P(x)=x42ax2+1P(x)=x^4-2ax^2+1. In the quadratic case, palindromic symmetry forces the recurrence to be the Legendre three-term recurrence; in the quartic case, the odd sector is Legendre and the even sector satisfies a two-component recurrence with palindromic coefficients. We conjecture this pattern -- palindromic PP forcing symmetric recurrence coefficients -- holds in all even degrees. The same dictionary governs the K\"{a}hler side ΩA1/dA\Omega^1_A/dA: all sectors reduce to the sector-11 family at a rescaled parameter, and the recurrence and ODE entries are canonical while the mixed-cocycle entry is partially choice-dependent.

Keywords

Cite

@article{arxiv.2605.02530,
  title  = {A partial dictionary between universal central extensions and orthogonal polynomials in the superelliptic Krichever--Novikov setting},
  author = {Felipe Albino dos Santos},
  journal= {arXiv preprint arXiv:2605.02530},
  year   = {2026}
}