Higher-rank tensor product decomposition conjecture for positive representations

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Let Uqq~(gR)\mathcal{U}_{q\widetilde{q}}(\mathfrak{g}_\mathbb{R}) be the modular-double quantum group and let Pα\mathcal{P}_{\alpha} and Pβ\mathcal{P}_{\beta} be positive representations. Write

γ→=∑α∈Δ+γαωα,\overrightarrow{\gamma}=\sum_{\alpha\in\Delta_+}\gamma_\alpha\omega_\alpha,

where the sum ranges over all positive roots, γα∈R+\gamma_\alpha\in\mathbb{R}_+, and ωα\omega_\alpha are the fundamental weights, with ωα:=ωα1+ωα2\omega_\alpha:=\omega_{\alpha_1}+\omega_{\alpha_2} when α:=α1+α2\alpha:=\alpha_1+\alpha_2 is not simple. Tensor product decomposition conjecture. The positive representations are closed under tensor products, with decomposition

Pα⊗Pβ≃∫R+N⊕Pγ→ dμ(γ→),\mathcal{P}_{\alpha}\otimes\mathcal{P}_{\beta}\simeq\int_{\mathbb{R}_+^N}^{\oplus}\mathcal{P}_{\overrightarrow{\gamma}}\,d\mu(\overrightarrow{\gamma}),

where

dμ(γ→)=∏α∈Δ+sinh⁡(2πbγα)sinh⁡(2πb−1γα) dγα.d\mu(\overrightarrow{\gamma})=\prod_{\alpha\in\Delta_+}\sinh(2\pi b\gamma_\alpha)\sinh(2\pi b^{-1}\gamma_\alpha)\,d\gamma_\alpha.

This conjecture would extend the known rank-one tensor product decomposition to higher rank and provide the continuous analogue of canonical-basis decompositions. The required functional-analytic treatment and the general higher-rank intertwining transformations remain to be established.

References

Primary source

Ivan Chi-Ho Ip, “Positive representations, multiplier Hopf algebra, and continuous canonical basis”, arXiv:1312.3207 (2014).

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