The exact asymptotic formula conjecture for unit-circle Turán sums

From papers

Let α>0\alpha>0 be constant, and define

Gn(α)=infzkC,zk=1maxν=1,,αn2k=1nzkν.G_n(\alpha)=\inf_{z_k\in\mathbb C,\,|z_k|=1}\max_{\nu=1,\ldots,\lfloor\alpha n^2\rfloor}\left|\sum_{k=1}^n z_k^\nu\right|.

Theorem avsavs gives

(B(α)o(1))nGn(α)(B(α)+o(1))n,(\underline B(\alpha)-o(1))\sqrt n\leq G_n(\alpha)\leq(\overline B(\alpha)+o(1))\sqrt n,

where

B(α)={1,0<α1,3212α,1α3,22α,3α,B(α)={1,0<α1,2,1<α2,3,2<α3,2,3<α.\underline B(\alpha)=\begin{cases}1,&0<\alpha\leq1,\sqrt{\frac32-\frac1{2\alpha}},&1\leq\alpha\leq3,\sqrt{2-\frac2\alpha},&3\leq\alpha,\end{cases} \qquad \overline B(\alpha)=\begin{cases}1,&0<\alpha\leq1,\sqrt2,&1<\alpha\leq2,\sqrt3,&2<\alpha\leq3,\\2,&3<\alpha.\end{cases}

Exact unit-circle asymptotic conjecture. One can choose B(α)=B(α)=B(α)B(\alpha)=\underline B(\alpha)=\overline B(\alpha) in Theorem avsavs. This conjecture would close the gap between the known lower and upper asymptotic bounds for unit-modulus points. The bounds coincide for 0<α10<\alpha\leq1, while the general case remains open.

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Sources & referencesView supporting material

Primary source

Johan Andersson, “Turan's problem 10 revisited”, arXiv:math/0609271 (2007).

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