# On the distance between homotopy classes in $W^{1/p,p}({\mathbb S}^1;{\mathbb S}^1)$

 Orateur: SHAFRIR Itai Localisation: Technion, Israël Type: Groupe de travail équations aux dérivées partielles Site: UPEC Salle: P1 028 Date de début: 21/09/2017 - 14:00 Date de fin: 21/09/2017 - 14:00

Abstract: For every $p\in(1,\infty)$ there is a natural notion of topological degree for maps in $W^{1/p,p}({\mathbb S}^1;{\mathbb S}^1)$ which allows us to write that space as a disjoint union of classes, $W^{1/p,p}({\mathbb S}^1;{\mathbb S}^1)=\bigcup_{d \in{\mathbb Z}}\mathcal{E}_d$. For every pair $d_1, d_2 \in \mathbb Z$, we show that the distance $Dist_{W^{1/p,p}}({\mathcal E}_{d_1}, {\mathcal E}_{d_2}):= \sup_{f \in{\mathcal E}_{d_1}} \inf_{g \in{\mathcal E}_{d_2}}\ d_{W^{1/p,p}}(f, g)$ equals the minimal $W^{1/p,p}$-energy in $\mathcal{E}_{d_1-d_2}$. In the special case $p=2$ we deduce from the latter formula an explicit value: $Dist_{W^{1/2,2}}({\mathcal E}_{d_1}, {\mathcal E}_{d_2})=2\pi |d_2-d_1|^{1/2}$.