Lukic's decomposition conjecture for higher-order Szegő sum rules

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Let ww be the density of the absolutely continuous part of a measure on the unit circle, let α=(αn)n≥0\alpha=(\alpha_n)_{n\geq 0} be its Verblunsky-coefficient sequence, and let SS be the left shift operator, (Sα)n=αn+1(S\alpha)_n=\alpha_{n+1}. For distinct θ1,…,θk∈[0,2π)\theta_1,\ldots,\theta_k\in[0,2\pi) and strictly positive integers m1,…,mkm_1,\ldots,m_k, let m=max⁡1≤j≤kmjm=\max_{1\leq j\leq k}m_j. Lukic's conjecture. The finiteness condition

∫02π∏j=1k(1−cos⁡(θ−θj))mjlog⁡w(θ)dθ2π>−∞\int_{0}^{2\pi}\prod_{j=1}^{k}\bigl(1-\cos(\theta-\theta_j)\bigr)^{m_j}\log w(\theta)\frac{d\theta}{2\pi}>-\infty

is equivalent to the existence of sequences β(1),…,β(k)\beta^{(1)},\ldots,\beta^{(k)} such that

α=β(1)+β(2)+⋯+β(k),\alpha=\beta^{(1)}+\beta^{(2)}+\cdots+\beta^{(k)},

with

(S−e−iθj)mjβ(j)∈ℓ2\bigl(S-e^{-i\theta_j}\bigr)^{m_j}\beta^{(j)}\in\ell^2

and

β(j)∈ℓ2mj+2\beta^{(j)}\in\ell^{2m_j+2}

for every jj. This refinement replaces the false pair of global conditions in Simon's conjecture and is presented as an improved conjecture.

References

Primary source

Zhihua Du, “Sum rules and Simon spectral gem problem on higher order Szegő theorems”, arXiv:2312.01323 (2023).

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