Modified higher-order Szegő conjecture for orthogonal polynomials on the unit circle

Let μ\mu be a probability measure on the unit circle with infinite support, write

dμ=w(θ)dθ2π+dμs,d\mu=w(\theta)\frac{d\theta}{2\pi}+d\mu_{\mathrm{s}},

and let α={αn}n=0\alpha=\{\alpha_n\}_{n=0}^{\infty} be its Verblunsky coefficients. Let SS be the shift on sequences, (Sx)n=xn+1(Sx)_n=x_{n+1}. For m1,,mlNm_1,\dots,m_l\in\mathbb{N} and distinct θ1,,θl[0,2π)\theta_1,\dots,\theta_l\in[0,2\pi), define the conditions

α=β(1)++β(l),\alpha=\beta^{(1)}+\cdots+\beta^{(l)}, (Seiθk)mkβ(k)2,(S-e^{-i\theta_k})^{m_k}\beta^{(k)}\in\ell^2,

and

β(k)2mk+2for all k.\beta^{(k)}\in\ell^{2m_k+2}\quad\text{for all }k.

Modified higher-order Szegő conjecture. The weighted logarithmic integrability condition

k=1l(1cos(θθk))mklogw(θ)dθ2π>\int\prod_{k=1}^l(1-\cos(\theta-\theta_k))^{m_k}\log w(\theta)\frac{d\theta}{2\pi}>-\infty

is equivalent to the existence of sequences β(1),,β(l)\beta^{(1)},\dots,\beta^{(l)} satisfying all three displayed conditions.

Sources & referencesView supporting material

Primary source

Milivoje Lukic, “On a conjecture for higher-order Szego theorems”, arXiv:1210.6953 (2012).

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