On Schurs exponent conjecture and its relation to Noether's Rationality problem

Noether's problem for orientation $p$-subgroups of symmetric groups

We give a positive solution to Noether's rationality problem for certain index $p$ subgroups of the $p$-Sylow subgoups of symmetric groups.

Schur定理及其与非阿贝尔张量积闭包性质的关系

Schur's theorem and its relation to the closure properties of the non-abelian tensor product

本文研究了Noetherian群的Schur乘子生成性及非阿贝尔张量积的闭包性质，提出了Schur定理的新版本。

On a rationality problem for fields of cross-ratios

Let $k$ be a field, $n \geqslant 5$ be an integer, $x_1, \dots, x_n$ be independent variables and $L_n = k(x_1, \dots, x_n)$. The symmetric group $S_n$ acts on $L_n$ by permuting the variables, and the projective linear group ${\rm PGL}_2$ acts by applying (the same) fractional linear transformation to each varaible. The fixed field $L_n^{{\rm PGL}_2}$ is called "the field of cross-ratios". Let $S \subset S_n$ be a subgroup. The Noether Problem asks whether the field extension $L_n^S/k$ is rational, and the Noether Problem for cross-ratios asks whether $K_n^S/k$ is rational. In an effort to re…

Bogomolov multipliers for some $p$-groups of nilpotency class 2

The Bogomolov multiplier $B_0(G)$ of a finite group $G$ is defined as the subgroup of the Schur multiplier consisting of the cohomology classes vanishing after restriction to all abelian subgroups of $G$. The triviality of the Bogomolov multiplier is an obstruction to Noether's problem. We show that if $G$ is a central product of $G_1$ and $G_2$, regarding $K_i\leq Z(G_i), i=1,2$, and $θ:G_1\to G_2$ is a group homomorphism such that its restriction $θ\vert_{K_1}:K_1\to K_2$ is an isomorphism, then the triviality of $B_0(G_1/K_1), B_0(G_1)$ and $B_0(G_2)$ implies the triviality of $B_0(G)$. We …