Algebraic versus geometric 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, and let E1,,EsE_1,\dots,E_s be its irreducible components. Let amt,T(λ0)\mathop{\rm am}\nolimits_{\mathbf{t},T}(\lambda_0) denote the algebraic multiplicity and gmt,T(λ0)\mathop{\rm gm}\nolimits_{\mathbf{t},T}(\lambda_0) the dimension of the eigenscheme. Algebraic versus geometric multiplicity conjecture.

amt,T(λ0)i=1sdim(Ei)ddim(Ei)1\mathop{\rm am}\nolimits_{\mathbf{t},T}(\lambda_0)\ge\sum_{i=1}^s \dim(E_i)d^{\dim(E_i)-1}

and

amt,T(λ0)gmt,T(λ0)dgmt,T(λ0)1.\mathop{\rm am}\nolimits_{\mathbf{t},T}(\lambda_0)\ge \mathop{\rm gm}\nolimits_{\mathbf{t},T}(\lambda_0)d^{\mathop{\rm gm}\nolimits_{\mathbf{t},T}(\lambda_0)-1}.

The second inequality is weaker than the first because some irreducible component has dimension equal to the geometric multiplicity. The conjecture is known for some special families of tensors arising from hypergraphs, but remains open in general.

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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