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

Let ww be the density of the absolutely continuous part of a measure on the unit circle, let α=(αn)n0\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=max1jkmjm=\max_{1\leq j\leq k}m_j. Lukic's conjecture. The finiteness condition

02πj=1k(1cos(θθj))mjlogw(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

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

and

β(j)2mj+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.

Sources & referencesView supporting material

Primary source

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

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