题目: Canonical bases of tensor products and positivity properties

时间：2026年05月28日14：00-15：00

地点：管理科研楼1418

摘要: We prove that the canonical basis of a modified quantum group $\dot{\mathbf{U}}$ exhibits strong positivity properties for the basis elements arising from spherical parabolic subalgebras. Our main result establishes that the structure constants for both the multiplication with arbitrary canonical basis elements in $\dot{\mathbf{U}}$ and the action on the canonical basis elements of arbitrary tensor products of simple lowest and highest weight modules by these elements belong to $\mathbb{N}[v,v^{-1}]$. This implies, in particular, for quantum groups of finite type, the structure constants for multiplication and for action on tensor product with respect to canonical basis are governed by positive coefficients. A key ingredient is our thickening construction, an algebraic technique that embeds a suitable approximation of the tensor of a lowest weight module and a highest weight module of $\dot{\mathbf{U}}$ into the negative part $\tilde{\mathbf{U}}^-$ of a larger quantum group. This allows us to inherit the desired positivity for the tensor product from the well-established positivity of the canonical basis of $\tilde{\mathbf{U}}^-$. This is a joint work with Xuhua He.

简介：方杰鹏，现为香港大学博士后，2022年博士毕业于清华大学。研究方向为表示论，主要集中在箭图表示与Hall代数，量子群与典范基。