Gross–Witten sum-rule conjecture for coupling below minus one

Let μM1(T)\mu\in\mathcal M_1(\mathbb T) have Verblunsky coefficients (αk)k0DN(\alpha_k)_{k\geq 0}\in\mathbb D^{\mathbb N}. Let θg\theta_{\tt g}, NN^-, N+N^+, λi+\lambda_i^+, λi\lambda_i^-, and Fg±\mathcal F_{\tt g}^{\pm} be the quantities associated with the Gross–Witten model, and let S1T(πθg,π+θg)\mathcal S_1^{\mathbb T}(\pi-\theta_{\tt g},\pi+\theta_{\tt g}) denote the stated admissible class. For μS1T(πθg,π+θg)\mu\in\mathcal S_1^{\mathbb T}(\pi-\theta_{\tt g},\pi+\theta_{\tt g}) and any g<1{\tt g}<-1, Gross–Witten sum-rule conjecture.

K(GWgμ)+i=1NFg+(λi+)+i=1N+Fg(λi)=H(g)g(α0k=1αkαˉk1)k=0log(1αk2),\mathcal K(\operatorname{GW}_{\tt g}\mid\mu)+\sum_{i=1}^{N^-}\mathcal F_{\tt g}^+(\lambda_i^+)+\sum_{i=1}^{N^+}\mathcal F_{\tt g}^-(\lambda_i^-)=H({\tt g})-{\tt g}\,\Re\left(\alpha_0-\sum_{k=1}^{\infty}\alpha_k\bar\alpha_{k-1}\right)-\sum_{k=0}^{\infty}\log(1-|\alpha_k|^2),

where HH is defined by the formula given in the source. If μS1T(πθg,π+θg)\mu\notin\mathcal S_1^{\mathbb T}(\pi-\theta_{\tt g},\pi+\theta_{\tt g}), the right-hand side is ++\infty. This conjectures the extension of the Gross–Witten sum rule beyond the regime g1|{\tt g}|\leq 1; the supplied text does not state whether it has been proved or disproved.

Sources & referencesView supporting material

Primary source

Fabrice Gamboa, Jan Nagel and Alain Rouault, “Sum rules and large deviations for spectral measures on the unit circle”, arXiv:1604.06934 (2017).

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