Positivity properties of canonical bases
数学专题报告
报告题目(Title)：Positivity properties of canonical bases
报告人(Speaker)：方杰鹏（香港大学）
地点(Place)：后主楼1220
时间(Time)：2025年10月22日（周三）16:30-17:30
邀请人(Inviter)：肖杰、覃帆、周宇
报告摘要
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 Professor Xuhua He.
