Braid groups of normalizers of reflection subgroups

Representations of braid groups via conjugation actions on congruence subgroups

We construct two families of representations of the braid group $B_n$ by considering conjugation actions on congruence subgroups of $GL_{n-1}(Z[t^{\pm 1},q^{\pm 1}])$. We show that many of these representations are faithful modulo the center of $B_n$.

复辫子群的抛物子群：剩余情形

Parabolic subgroups of complex braid groups: the remaining case

本文利用复辫子群 B(G31) 的 Garside 广群结构，证明 Marin 和 González-Meneses 关于抛物子群的主要定理，补全了此前唯一遗留情形。

Character correspondeces in solvable groups with a self-normalizing Sylow subgroup

In 1973, I. M. Isaacs described a correspondence between characters of degree not divisible by a fixed prime $p$ of a finite solvable group $G$ and those of the normalizer of Sylow $p$-subgroup of $G$, whenever the index of the normalizer in $G$ is odd. This correspondence is natural in the sense that an algorithm is provided to compute it, and the result of the application of the algorithm does not depend on choices made. Later on, for $p$-solvable groups with self-normalizing Sylow $p$-subgroup, G. Navarro showed that every irreducible character of degree not divisible by $p$ has a unique li…

辫群模其同余子群的商群

Quotients of braid groups by their congruence subgroups

该研究解决了Dan Margalit提出的公开问题，确定了辫群同余子群在整一般线性群中的像，并利用辛同余子群刻画了辫群模同余子群的商群结构。

复辫子群的抛物子群

Parabolic subgroups of complex braid groups

本文针对与任意不可约复反射群相关的广义辫子群引入抛物子群类，证明其构成格且每个元素有抛物闭包，还推广了曲线复形并猜想其双曲性。

On Extending Unipotent Representations to their Stabilizers

We show that irreducible unipotent representations of split Levi subgroups of finite groups of Lie type extend to their stabilizers inside the normalizer of the given Levi subgroup. For this purpose, we extend the multiplicity-freeness theorem from regular embeddings to arbitrary isotypies.

Congruence subgroups from representations of the three-strand braid group

Ng and Schauenburg proved that the kernel of a $(2+1)$-dimensional topological quantum field theory representation of $\mathrm{SL}(2, \mathbb{Z})$ is a congruence subgroup. Motivated by their result, we explore when the kernel of an irreducible representation of the braid group $B_3$ with finite image enjoys a congruence subgroup property. In particular, we show that in dimensions two and three, when the projective order of the image of the braid generator $σ_1$ is between 2 and 5 the kernel projects onto a congruence subgroup of $\mathrm{PSL}(2,\mathbb{Z})$ and compute its level. However, we …

On the automorphism group of the first Weyl algebra

Let $A_{1} := k [t, \partial ]$ be the first algebra over a field $k$ of characteristic zero. One can associate to each right ideal $I$ of $A_1$ its Stafford subgroup, which is a subgroup of $\Aut_k(A_1)$, the automorphism group of the ring $A_1$. In this article we show that each Stafford subgroup is equal to its normalizer. For that, we study when the Stafford subgroup of a right ideal of $A_1$ contains a given Stafford subgroup.

Higher limits over the fusion orbit category

The fusion orbit category $\overline{\mathcal F _{\mathcal C}} (G)$ of a discrete group $G$ over a collection $\mathcal C$ is the category whose objects are the subgroups $H$ in $\mathcal C$, and whose morphisms $H \to K$ are given by the $G$-maps $G/H \to G/K$ modulo the action of the centralizer group $C_G(H)$. We show that the higher limits over $\overline{\mathcal F _{\mathcal C}} (G)$ can be computed using the hypercohomology spectral sequences coming from the Dwyer $G$-spaces for centralizer and normalizer decompositions for $G$. If $G$ is the discrete group realizing a saturated fusion …

Stability conditions and braid group actions on affine $A_n$ quivers

We study stability conditions on the Calabi-Yau-$N$ categories associated to an affine type $A_n$ quiver which can be constructed from certain meromorphic quadratic differentials with zeroes of order $N-2$. We follow Ikeda's work to show that this moduli space of quadratic differentials is isomorphic to the space of stability conditions quotient by the spherical subgroup of the autoequivalence group. We show that the spherical subgroup is isomorphic to the braid group of affine type $A$ based on Khovanov-Seidel-Thomas method.