Session 11. Geometric Analysis and Related Topics

A remark on the Lavrentiew gap phenomenon for harmonic maps into spheres

Katarzyna Mazowiecka,  University of Warsaw, Poland
The talk is based on the joint work with Paweł Strzelecki
We prove that for each positive integer \(N\) the set of smooth, zero degree maps \(\psi:\mathbb{S}^2\to \mathbb{S}^2\) which have the following three properties:
  1. there is a unique minimizing harmonic map \(u: \mathbb{B}^3\to S^2\) which satisfies the prescribed boundary condition \(u\mid_{\partial \mathbb{B}^3}=\psi\);
  2. this map \(u\) has at least \(N\) singular points in \(\mathbb{B}^3\);
  3. the Lavrentiev gap phenomenon holds for \(\psi\), i.e., \[ \min_{W^{1,2}_{\psi}(\mathbb{B}^3,\mathbb{S}^2)}E(u) < \inf_{W^{1,2}_{\psi}(\mathbb{B}^3,\mathbb{S}^2)\cap C^0(\overline{\mathbb{B}}^3)} E(u), \] where \(W^{1,2}_{\psi}(\mathbb{B}^3,\mathbb{S}^2)=\{v\in W^{1,2}(\mathbb{B}^3,\mathbb{S}^2):v\!\mid_{\partial\mathbb{B}^3}=\psi\text{ in the trace sense}\}\),
is dense in the set of all smooth zero degree maps \(\phi: \mathbb{S}^2\to\mathbb{S}^2\) endowed with the \(H^{1/2}\)-topology.
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