Normalized concentrating solutions to nonlinear elliptic problems

We prove the existence of solutions $(\lambda, v)\in $\mathbb{R}$\times H^{1}(\Omega)$ of the elliptic problem $$\{\begin{array}{ll}-\mathrm{\Delta }v+(V(x)+\lambda )v=v^p& \text{ in }\mathrm{\Omega },v>0,{\int }_{\mathrm{\Omega }}{v}^{2}dx=\rho \mathrm{.}\end{array}$$ Any $v$ solving such problem (for some $\lambda$) is called a normalized solution, where the normalization is settled in $L^2(\mathrm{\Omega })$. Here $\mathrm{\Omega }$ is either the whole space ${\mathbb{R}}^N$ or a bounded smooth domain of ${\mathbb{R}}^N$, in which case we assume $V\equiv 0$ and homogeneous Dirichlet or Neumann boundary conditions. Moreover, $1<p<\frac{N+2}{N-2}$ if $N\ge 3$ and $p>1$ if $N=1,2$. Normalized solutions appear in different contexts, such as the study of the Nonlinear Schr"odinger equation, or that of quadratic ergodic Mean Field Games systems. We prove the existence of solutions concentrating at suitable points of $\mathrm{\Omega }$ as the prescribed mass $\rho$ is either small (when $p<1+\frac{4}{N}$) or large (when $p>1+\frac{4}{N}$) or it approaches some critical threshold (when $p=1+\frac{4}{N}$).