Simon's higher-order Szegő sum-rule conjecture

About 14 years old · traced to

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,θ2,…,θk∈[0,2π)\theta_1,\theta_2,\ldots,\theta_k\in[0,2\pi) and strictly positive integers m1,m2,…,mkm_1,m_2,\ldots,m_k, set m=max⁡1≤j≤kmjm=\max_{1\leq j\leq k}m_j. Simon's higher-order Szegő conjecture. The 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

should be equivalent to

∑n=0∞(∣{∏j=1k(S−e−iθj)mjα}n∣2+∣αn∣2m+2)<∞.\sum_{n=0}^{\infty}\left(\left|\left\{\prod_{j=1}^{k}\bigl(S-e^{-i\theta_j}\bigr)^{m_j}\alpha\right\}_n\right|^{2}+|\alpha_n|^{2m+2}\right)<\infty.

This conjecture was subsequently shown to be false: for θ1=0\theta_1=0, θ2=π\theta_2=\pi, and m1=m2=1m_1=m_2=1, Lukic constructed a counterexample for which the sequence condition holds but the integral equals −∞-\infty.

References

Primary source

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

Additional references

2 papers in this index state this conjecture (2012–2023). The statement above is taken from the most recent of them; the others are arXiv:1210.6953.

Progress summary

Never refreshed

Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.

Solutions 0

No solutions have been posted yet.