Algebraic versus span multiplicity conjecture for tensor eigenvalues

Let n,dn,d be positive integers, let T,tCn((Cn))dT,\mathbf{t}\in\mathbb{C}^n\otimes((\mathbb{C}^n)^*)^{\otimes d}, and assume that t\mathbf{t} is non-singular. For λ0C\lambda_0\in\mathbb{C}, let Et,T(λ0)E_{\mathbf{t},T}(\lambda_0) be the eigenscheme of t\mathbf{t}-eigenvectors of TT with eigenvalue λ0\lambda_0, let amt,T(λ0)\mathop{\rm am}\nolimits_{\mathbf{t},T}(\lambda_0) be the multiplicity of λ0\lambda_0 as a root of the t\mathbf{t}-characteristic polynomial, and let smt,T(λ0)\mathop{\rm sm}\nolimits_{\mathbf{t},T}(\lambda_0) be the dimension of the linear span of those eigenvectors. Algebraic versus span multiplicity conjecture. If λ0C\lambda_0\in\mathbb{C}, then

amt,T(λ0)smt,T(λ0).\mathop{\rm am}\nolimits_{\mathbf{t},T}(\lambda_0)\ge\mathop{\rm sm}\nolimits_{\mathbf{t},T}(\lambda_0).

This conjecture generalizes the matrix inequality between geometric and algebraic multiplicities to tensor eigenvalues, for which the relations among algebraic, geometric, and span multiplicities are not fully understood. Its status is not established in the supplied text.

Sources & referencesView supporting material

Primary source

Stefano Canino, Cosimo Flavi, Francesco Galuppi and Yuze Luan, “New conjectures on multiplicities of tensor eigenvalues”, arXiv:2607.21422 (2026).

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