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High order Fuchsian equations for the square lattice Ising model: \(\widetilde{\chi}^{(5)}\). (English) Zbl 1171.82005

Summary: We consider the Fuchsian linear differential equation obtained (modulo a prime) for \(\widetilde{\chi}^{(5)}\), the five-particle contribution to the susceptibility of the square lattice Ising model. We show that one can understand the factorization of the corresponding linear differential operator from calculations using just a single prime. A particular linear combination of \(\widetilde{\chi}^{(1)}\) and \(\widetilde{\chi}^{(3)}\) can be removed from \(\widetilde{\chi}^{(5)}\) and the resulting series is annihilated by a high order globally nilpotent linear ODE. The corresponding (minimal order) linear differential operator, of order 29, splits into factors of small orders. A fifth-order linear differential operator occurs as the left-most factor of the ‘depleted’ differential operator and it is shown to be equivalent to the symmetric fourth power of \(L_{E}\), the linear differential operator corresponding to the elliptic integral \(E\). This result generalizes what we have found for the lower order terms \(\widetilde{\chi}^{(3)}\) and \(\widetilde{\chi}^{(4)}\). We conjecture that a linear differential operator equivalent to a symmetric \((n - 1)\) th power of \(L_{E}\) occurs as a left-most factor in the minimal order linear differential operators for all \(\widetilde{\chi}^{(n)}\)’s.

MSC:

82B20 Lattice systems (Ising, dimer, Potts, etc.) and systems on graphs arising in equilibrium statistical mechanics
34M55 Painlevé and other special ordinary differential equations in the complex domain; classification, hierarchies
47E05 General theory of ordinary differential operators
81Qxx General mathematical topics and methods in quantum theory
32G34 Moduli and deformations for ordinary differential equations (e.g., Knizhnik-Zamolodchikov equation)
34Lxx Ordinary differential operators
34Mxx Ordinary differential equations in the complex domain
14Kxx Abelian varieties and schemes