A new proof on quasilinear Schrödinger equations with prescribed mass and combined nonlinearities

In this work, we study the quasilinear Schrödinger equation \begin{equation*} \aligned -Δu-Δ(u^2)u=|u|^{p-2}u+|u|^{q-2}u+λu,,, x\in\R^N, \endaligned \end{equation*} under the mass constraint \begin{equation*} \int_{\R^N}|u|^2\text{d}x=a, \end{equation*} where $N\geq2$, $2<p<2+\frac{4}{N}<4+\frac{4}{N}<q<22^$, $a>0$ is a given mass and $λ$ is a Lagrange multiplier. As a continuation of our previous work (Chen et al., 2025, arXiv:2506.07346v1), we establish some results by means of a suitable change of variables as follows: \begin{itemize} \item[{\bf(i) }] {\bf qualitative analysis of the constrained minimization}\ For $2<p<4+\frac{4}{N}\leq q<22^$, we provide a detailed study of the minimization problem under some appropriate conditions on $a>0$; \end{itemize} \begin{itemize} \item[{\bf(ii)}]{\bf existence of two radial distinct normalized solutions}\ For $2<p<2+\frac{4}{N}<4+\frac{4}{N}<q<22^$, we obtain a local minimizer under the normalized constraint;\ For $2<p<2+\frac{4}{N}<4+\frac{4}{N}<q\leq2^$, we obtain a mountain pass type normalized solution distinct from the local minimizer. \end{itemize} Notably, the second result {\bf (ii)} resolves the open problem {\bf(OP1)} posed by (Chen et al., 2025, arXiv:2506.07346v1). Unlike previous approaches that rely on constructing Palais-Smale-Pohozaev sequences by [Jeanjean, 1997, Nonlinear Anal. {\bf 28}, 1633-1659], we obtain the mountain pass solution employing a new method, which lean upon the monotonicity trick developed by (Chang et al., 2024, Ann. Inst. H. Poincaré C Anal. Non Linéaire, {\bf 41}, 933-959). We emphasize that the methods developed in this work can be extended to investigate the existence of mountain pass-type normalized solutions for other classes of quasilinear Schrödinger equations.

💡 Research Summary

This paper investigates the normalized (fixed‑mass) solutions of the quasilinear Schrödinger equation
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