nLab effective group action


this entry is about the concept in group theory; for the concept in quantumfield theory see at effective action functional; for disambiguation see effective action


Group Theory

Representation theory



A group action is effective if no group element other than the neutral element acts trivially on all elements of the space, hence if no other element acts the way the neutral element does.


A group action of a group (group object) GG on a set (object) XX is effective if xXgx=x\underset{x \in X}{\forall} g x = x implies that g=eg = e is the neutral element.

Beware the similarity to and difference with free action: a free action is effective, but an effective action need not be free.

Last revised on November 4, 2021 at 05:56:42. See the history of this page for a list of all contributions to it.