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Linear representations of algebras and groups, Lie theory, associative algebras, multilinear algebra.

3 votes
1 answer
111 views

Projectivity of some module

Let $k$ be a algebraically closed field and suppose that $A$ and $B$ are finite dimensional $k$-algebras. If we assume that $A$ is a symmetric $k$-algebra and $A\otimes_k I$ is a projective $A\otimes_ …
3 votes
0 answers
207 views

A question related to the polynomial ring $R[x]$ over some principal ideal domain $R$?

Let $R[x]$ be the polynomial ring over some principal ideal domain $R$. If $R[x]/I$ is free as a $R$-module for some ideal $I$, is $I$ a principal ideal which is generated by some monic polynomial in …
2 votes
1 answer
129 views

Indecomposable representations for group ring $RG$ over commutative ring $R$ with characteri...

Given a field $k$ with characteristic $p$ and a finite cyclic $p$-group $G$ of order $p^a$, it is well-known that all the indecomposable representations of $kG$ are given by mapping a generator $x$ of …
0 votes
1 answer
178 views

Dimension of projective cover of trivial $kG$-module

Given a field $k$ with characteristic $p$, let $G$ be a transitive permutation group on $4p$ points. Let $P$ be a Sylow $p$-subgroup of $G$ and $Q\leq P$ is a $p$-subgroup of $P$ of index $p$. Now den …
5 votes
2 answers
349 views

Is this quiver with relations of finite representation type

Let $Q=(Q_0,Q_1)$ be the following quiver, $Q_0$ consist of 2 vertices, denoted by 1,2. $Q_1$ consist a loop at 1 called $\gamma$, an arrow $\alpha$ from 1 to 2 and an arrow $\beta$ from 2 to 1. The r …
3 votes
1 answer
93 views

Nontrivial self-extension of trivial $kG$-module

For a sufficient large field $k$ with characteristic 2, $S_3$ and $D_{10}$ both do have the property that the trivial module over their group algebra has nontrivial self-extension. Puig's work on nilp …
8 votes
1 answer
193 views

Is there always a simple module whose Green correspondent is a simple module under some cond...

Let $G$ be a finite group and $KG$ its group algebra over some field $K$ with $\mathrm{char}\ K$ dividing the order of $G$. It's well-known that the Green correspondence is compatible with the Brauer …
6 votes
2 answers
367 views

Is there a countable discrete infinite group $G$ over which the group algebra $\mathbb{C} G$...

I am seeking for an Artin $k$-algebra (especially for group algebra) which is infinite-dimensional over some field $k$. It's known that any complex group algebra has trivial Jacobson radical. So I hav …
1 vote
0 answers
131 views

A question concerning extension groups between simple modules

$\DeclareMathOperator\Ext{Ext}\DeclareMathOperator\pd{pd}$Let A be a finite dimensional algebra over some field k with exactly m simple modules up to isomorphism. Let S be a simple left A-module. Supp …
4 votes
1 answer
158 views

Can we always choose 2 nonisomorphic simple modules to satisfy the following nonvanishing ex...

$\DeclareMathOperator\Ext{Ext}\DeclareMathOperator\pd{pd}$Let A be a finite dimensional algebra over some field k and S a nonprojective simple left A-module. Suppose the projective dimension $\pd_A(S) …
4 votes
1 answer
269 views

Is the fixed subring a symmetric algebra?

Let A be a finite dimensional symmetric k-algebra over some field k. The set of units of A is denoted by U(A). Suppose G is a cyclic group of prime order which acts via inner algebra automorphism on A …
4 votes
0 answers
78 views

Is Broué's abelian defect conjecture true for finite groups with abelian TI Sylow p-subgroups?

I am now interested in Broué's abelian defect conjecture and I have read many papers concerning it. For a prime $p$, I informally define a finite group to be a $p$-ATI-group if it has abelian Sylow $p …