The signless Laplacian spectral Turán problems for hypergraphs

Abstract: Let $\mathcal{H}=(V, E)$ be an $r$-uniform hypergraph on $n$ vertices. The signless Laplacian spectral radius of $\mathcal{H}$ is defined as the maximum modulus of the eigenvalues of the tensor $\mathcal{Q}(\mathcal{H})=\mathcal{D}(\mathcal{H})+\mathcal{A}(\mathcal{H})$, where $\mathcal{D}(\mathcal{H})$ and $\mathcal{A}(\mathcal{H})$ are the diagonal tensor of degrees and adjacency tensor of $G$, respectively. In this paper, we establish a general theorem that extends the spectral Turán result of Keevash, Lenz and Mubayi [SIAM J. Discrete Math., 28 (4) (2014)] to the setting of signless Laplacian spectral Turán problems. We prove that for any family $\mathcal{F}$ of $r$-uniform hypergraphs that is degree-stable with respect to a family $\mathcal{H}_n$ of $r$-uniform hypergraphs and whose extremal constructions satisfy certain natural assumptions, the signless Laplacian spectral Turán problem can be effectively reduced to the corresponding problem restricted to the family $\mathcal{H}_n$. As a concrete application, we completely characterize the signless Laplacian spectral extremal hypergraph for the Fano plane.