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

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.

Sources & referencesView supporting material

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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