Hu–Ye's eigenvariety bound for tensor eigenvalue multiplicity

Let A\mathcal{A} be a kk-th order, nn-dimensional tensor, let λ\lambda be an eigenvalue, and let

Vλ(A)=ccn\mathcal{V}_{\lambda}(\mathcal{A})=ccn

be its eigenvariety. Suppose that this variety has irreducible components V1,,VκV_1,\ldots,V_\kappa, and write am(λ)\mathrm{am}(\lambda) for the algebraic multiplicity and gm(λ)\mathrm{gm}(\lambda) for the maximum dimension of an irreducible component. Hu–Ye's conjecture.

am(λ)i=1κdim(Vi)(k1)dim(Vi)1,\mathrm{am}(\lambda) \geq \sum_{i=1}^{\kappa} \mathrm{dim}(V_i)(k-1)^{\mathrm{dim}(V_i)-1},

and, in particular,

am(λ)gm(λ)(k1)gm(λ)1.\mathrm{am}(\lambda) \geq \mathrm{gm}(\lambda)(k-1)^{\mathrm{gm}(\lambda)-1}.

Hu and Ye proposed this bound in 2016 and proved it in several cases; the paper studies further cases, but the general assertion remains open.

Sources & referencesView supporting material

Primary source

Yi-Zheng Fan, “The multiplicity of eigenvalues of nonnegative weakly irreducible tensors and uniform hypergraphs”, arXiv:2410.20830 (2024).

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