Nakajima's canonical tensor-product isomorphism conjecture for quiver varieties

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Let \tilde{\frac?} be the tensor product variety associated with dominant weights λ1,λ2\lambda_1,\lambda_2, and let ω1,ω2\omega^1,\omega^2 be the corresponding framing data, with ω=ω1+ω2\omega=\omega^1+\omega^2. The Borel–Moore homology groups H(L(ω1))\mathbf{H}(\mathfrak{L}(\omega^1)), H(L(ω2))\mathbf{H}(\mathfrak{L}(\omega^2)), and H(Z~(ω))\mathbf{H}(\tilde{\mathfrak{Z}}(\omega)) carry their natural g\mathfrak{g}-module structures. Nakajima's canonical tensor-product isomorphism conjecture. There exists a unique isomorphism of g\mathfrak{g}-modules

φ~:H(L(ω1))⊗H(L(ω2))→H(Z~(ω))\tilde{\varphi}: \mathbf{H}(\mathfrak{L}(\omega^{1})) \otimes \mathbf{H}(\mathfrak{L}(\omega^{2})) \rightarrow \mathbf{H}(\tilde{\mathfrak{Z}}(\omega))

such that its restriction to [L(0,ω1)]⊗H(L(ω2))[\mathfrak{L}(0,\omega^{1})]\otimes \mathbf{H}(\mathfrak{L}(\omega^{2})) equals the composition of the Thom isomorphism

HtopBM(Z~1,Q)≅H(L(ω2))\mathbf{H}^{\mathrm{BM}}_{\mathrm{top}}(\tilde{\mathfrak{Z}}_{1},\mathbb{Q})\cong \mathbf{H}(\mathfrak{L}(\omega^{2}))

and the inclusion HtopBM(Z~1,Q)→H(Z~(ω))\mathbf{H}^{\mathrm{BM}}_{\mathrm{top}}(\tilde{\mathfrak{Z}}_{1},\mathbb{Q})\rightarrow \mathbf{H}(\tilde{\mathfrak{Z}}(\omega)). The conjecture identifies the tensor product of the two Nakajima modules canonically with the homology of the tensor product variety. It was proved for ADE quiver varieties by Nakajima; the supplied status evidence records the uniqueness property for the relevant irreducible components, while the general status is open.

References

Primary source

Jiepeng Fang and Yixin Lan, “Lusztig sheaves, characteristic cycles and the Borel-Moore homology of Nakajima's quiver varieties”, arXiv:2501.12047 (2025).

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