Palindromic symmetry conjecture for recurrence coefficients in superelliptic central extensions

Let A=C[x±1,uu2=P(x)]A=\mathbb{C}[x^{\pm1},u\mid u^2=P(x)], where P(x)C[x]P(x)\in\mathbb{C}[x] is palindromic of even degree 2r2r with simple roots. Let A/AA/\partial A denote the quotient by exact derivatives, whose reduction relations define recurrence coefficients indexed by degree. Palindromic symmetry conjecture. The identity

P(x)=x2rP(1/x)P(x)=x^{2r}P(1/x)

forces the recurrence coefficients in A/AA/\partial A to be symmetric in the degree index. For r=1r=1, this symmetry should imply, via Favard's theorem, that the associated polynomial family is orthogonal with respect to a symmetric measure; for r2r\geq 2, the recurrence is expected to be a multi-component system of dimension rr, requiring a block-Jacobi generalization. The claim is verified in the cases r=1r=1 and r=2r=2, while no assertion is made that symmetry alone forces the classical Jacobi class. This conjecture proposes a general structural link between palindromic branch-locus symmetry and recurrence relations in universal central extensions; the higher-degree multi-component case remains open, and the stated orthogonality discussion is established on the current-algebra side only for the cited type-AA' canonical family.

Sources & referencesView supporting material

Primary source

Felipe Albino dos Santos, “A partial dictionary between universal central extensions and orthogonal polynomials in the superelliptic Krichever–Novikov setting”, arXiv:2605.02530 (2026).

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