Sharp width-dependent Turán conjecture for convex domains

Let KCK\Subset\mathbb C be a compact convex domain. Denote by dd its diameter and by ww its width, let nNn\in\mathbb N, and let Pn(K)\mathcal P_n(K) denote the relevant class of polynomials of degree at most nn on KK. For q1q\ge 1, write Lq(K)\|\cdot\|_{L^q(\partial K)} for the boundary LqL^q norm.

Width-dependent Turán conjecture. There exists an absolute constant c>0c>0 such that, for every compact convex domain KCK\Subset\mathbb C and every pPn(K)p\in\mathcal P_n(K),

pLq(K)cwd2npLq(K).\|p'\|_{L^q(\partial K)}\ge c\frac{w}{d^2}n\|p\|_{L^q(\partial K)}.

This would sharpen the conjectured linear lower bound by identifying the geometric dependence through the width-to-diameter-squared ratio. The supplied passage presents it as a further sharpening motivated by the maximum-norm result and constructions giving matching order, but it does not establish the claim.

Sources & referencesView supporting material

Primary source

Polina Yu. Glazyrina and Szilárd Gy. Révész, “Turán-Erőd type converse Markov inequalities on general convex domains of the plane in L^q”, arXiv:1805.04822 (2018).

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