Necessary Conditions for Single-Critical-Point Higher-Order Szegő Sum Rules in OPUC
Fuente:
arXiv
Saved in:
| Main Author: | |
|---|---|
| Format: | Preprint |
| Published: |
2026
|
| Subjects: | |
| Online Access: | |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1866914540539609088 |
|---|---|
| author | Piao, Daxiong |
| author_facet | Piao, Daxiong |
| contents | We prove the necessity part of the higher-order Szegő theorem on the unit circle for the single-critical-point weights $H_m(e^{iθ})=(1-\cosθ)^m$, $m\ge1$. If $\{α_n\}_{n\ge0}$ are the Verblunsky coefficients of a nontrivial probability measure $dμ=w(θ)dθ/(2π)+dμ_{\mathrm s}$, then the weighted Szegő condition $\int_0^{2π}
(1-\cosθ)^m\log w(θ)\frac{dθ}{2π}>-\infty$ implies $Δ^mα\in\ell^2,
\,\,
α\in\ell^{2m+2}.$
The proof uses a finite-volume version of Yan's higher-order sum rule. The quadratic part yields the $m$-th difference energy, and the logarithmic tail yields the $\ell^{2m+2}$-control. The non-sign-definite critical terms are treated in two steps. First, the quartic principal critical block is isolated using the Yan quotient-algebra normal representative and shown to have a positive semidefinite Gram representation. Second, the remaining non-principal critical terms are controlled by the diagonal-vanishing property $\mathcal Y_{k,\mathrm{crit}}^{(m)}
\in
\mathfrak I_k^{\,m+1-k},
\,\, 2\le k\le m,$ together with the Breuer--Simon--Zeitouni normal form, discrete interpolation, and Young's inequality. These estimates yield a uniform finite-volume coercive bound, from which the necessity theorem follows for all $m\ge1$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_06722 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Necessary Conditions for Single-Critical-Point Higher-Order Szegő Sum Rules in OPUC Piao, Daxiong Spectral Theory Probability 42C05, 47B36, 30C15 We prove the necessity part of the higher-order Szegő theorem on the unit circle for the single-critical-point weights $H_m(e^{iθ})=(1-\cosθ)^m$, $m\ge1$. If $\{α_n\}_{n\ge0}$ are the Verblunsky coefficients of a nontrivial probability measure $dμ=w(θ)dθ/(2π)+dμ_{\mathrm s}$, then the weighted Szegő condition $\int_0^{2π} (1-\cosθ)^m\log w(θ)\frac{dθ}{2π}>-\infty$ implies $Δ^mα\in\ell^2, \,\, α\in\ell^{2m+2}.$ The proof uses a finite-volume version of Yan's higher-order sum rule. The quadratic part yields the $m$-th difference energy, and the logarithmic tail yields the $\ell^{2m+2}$-control. The non-sign-definite critical terms are treated in two steps. First, the quartic principal critical block is isolated using the Yan quotient-algebra normal representative and shown to have a positive semidefinite Gram representation. Second, the remaining non-principal critical terms are controlled by the diagonal-vanishing property $\mathcal Y_{k,\mathrm{crit}}^{(m)} \in \mathfrak I_k^{\,m+1-k}, \,\, 2\le k\le m,$ together with the Breuer--Simon--Zeitouni normal form, discrete interpolation, and Young's inequality. These estimates yield a uniform finite-volume coercive bound, from which the necessity theorem follows for all $m\ge1$. |
| title | Necessary Conditions for Single-Critical-Point Higher-Order Szegő Sum Rules in OPUC |
| topic | Spectral Theory Probability 42C05, 47B36, 30C15 |
| url | https://arxiv.org/abs/2605.06722 |