# Non-autonomous double phase eigenvalue problems with indefinite weight and lack of compactness

## TL;DR

This paper investigates eigenvalues for a double phase differential operator with unbalanced growth and indefinite weight, revealing different spectral structures depending on the relation between p and q.

## Contribution

It establishes the existence of continuous eigenvalue families for p<q and discrete diverging eigenvalues for q<p in a non-autonomous double phase problem.

## Key findings

- For p<q, a continuous spectrum of eigenvalues exists.
- For q<p, a discrete set of eigenvalues diverging to infinity.
- The problem handles indefinite weights and potential degeneracy.

## Abstract

In this paper, we consider eigenvalues to the following double phase problem with unbalanced growth and indefinite weight, $$ -\Delta_p^a u-\Delta_q u =\lambda m(x) |u|^{q-2}u \quad \mbox{in} \,\, \R^N, $$ where {$N \geq 2$}, {$1<p, q<N$, $p \neq q$}, ${a \in C^{0, 1}(\R^N, [0, +\infty))}$, $a \not\equiv 0$ and $m: \R^N \to \R$ is {an indefinite sign weight which may admit nontrivial positive and negative parts}. Here $\Delta_q$ is the $q$-Laplacian operator and $\Delta_p^a$ is the weighted $p$-Laplace operator defined by $\Delta_p^a u:=\textnormal{div}(a(x) |\nabla u|^{p-2} \nabla u)$. The problem can be degenerate, in the sense that the infimum of $a$ in $\R^N$ may be zero. Our main results distinguish between the cases $p<q$ and $q<p$. In the first case, we establish the existence of a {\it continuous} family of eigenvalues, starting from the principal frequency of a suitable single phase eigenvalue problem. In the latter case, we prove the existence of a {\it discrete} family of positive eigenvalues, which diverges to infinity.