Strong competition versus fractional diffusion: the case of Lotka-Volterra interaction

We consider a system of differential equations with nonlinear Steklov boundary conditions, related to the fractional problem $$(-\Delta)^s u_i = f_i(x,u_i) - \beta u_i^p \sum_{j\neq i} a_{ij} u_j^p,$$ where $i = i,\dots, k$, $s\in(0,1)$, $p>0$, $a_{ij}>0$ and $\beta>0$. When $k=2$ we develop a quasi-optimal regularity theory in $C^{0,\alpha}$, uniformly w.r.t. $\beta$, for every $\alpha < \alpha_{\mathrm opt}=min(1,2s)$; moreover we show that the traces of the limiting profiles as $\beta\to+\infty$ are Lipschitz continuous and segregated. Such results are extended to the case of $k\geq3$ densities, with some restrictions on $s$, $p$ and $a_{ij}$

Multidimensional entire solutions for an elliptic system modelling phase separation

For the system of semilinear elliptic equations $$\Delta V_i = V_i \sum_{j \neq i} V_j^2, \qquad V_i > 0 \qquad \text{in $\mathbb{R}^N$}$$ we devise a new method to construct entire solutions. The method extends the existence results already available in the literature, which are concerned with the 2-dimensional case, also in higher dimensions $N \ge 3$. In particular, we provide an explicit relation between orthogonal symmetry subgroups, optimal partition problems of the sphere, the existence of solutions and their asymptotic growth. This is achieved by means of new asymptotic estimates for competing system and new sharp versions for monotonicity formulae of Alt-Caffarelli-Friedman type.Comment: Final version: presentation of the results improved, and several minor corrections with respect to the first versio