Peakedness conjecture for extremal Sobolev functions

Let n2n \geq 2 and let ΩRn\Omega \subset \mathbf{R}^n be a bounded domain with piecewise Lipschitz boundary satisfying a uniform cone condition. For each allowable exponent pp, let upu_p^* be the corresponding positive extremal function, normalized by

supxΩup(x)=1.\sup_{x \in \Omega} u_p^*(x)=1.

Define its distribution function by

\mu_p(t)=\left|\left\\{x \in \Omega:u_p^*(x)>t\right\\}\right|.

Peakedness conjecture. Within the allowable range of exponents,

1p<qμp(t)>μq(t)for almost every t(0,1).1\leq p<q\quad\Rightarrow\quad \mu_p(t)>\mu_q(t) \quad\text{for almost every }t\in(0,1).

If n=2n=2, the allowable range is 1p<q1\leq p<q; if n3n\geq3, it is 1p<q<2nn21\leq p<q<\frac{2n}{n-2}. This formalizes the expectation that extremal functions become more peaked as pp increases; the paper presents numerical evidence, but the inequality remains conjectural.

Sources & referencesView supporting material

Primary source

Stefan Juhnke and Jesse Ratzkin, “A numerical investigation of level sets of extremal Sobolev functions”, arXiv:1401.2313 (2014).

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