Can prime fields act two ways on the same abelian group?

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SUMMARY

The discussion centers on the existence of two distinct actions, denoted as \cdot and \odot, of a field F on an abelian group V, where V serves as an F-module. A common approach to this problem involves utilizing a vector space over a field with a non-trivial automorphism group, defining the action \odot as f(r) \cdot \mu for f in Aut(F) with f not equal to the identity automorphism. The participants explore whether this method is the only viable solution and investigate the implications of prime fields acting in multiple ways on a module, noting that the trivial operation results in F.V being equivalent to zero.

PREREQUISITES
  • Understanding of abelian groups and their properties
  • Familiarity with field theory and vector spaces
  • Knowledge of automorphism groups and their significance
  • Concepts of direct and semidirect products in group theory
NEXT STEPS
  • Research the properties of automorphism groups in field theory
  • Study the implications of non-trivial automorphisms on vector spaces
  • Explore the differences between direct and semidirect products in group theory
  • Investigate examples of abelian groups that exhibit multiple actions by fields
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This discussion is beneficial for mathematicians, particularly those specializing in abstract algebra, group theory, and field theory, as well as graduate students seeking to deepen their understanding of module actions and automorphisms.

imurme8
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A problem asks to find an abelian group [itex]V[/itex] and a field [itex]F[/itex] such that there exist two different actions, call them [itex]\cdot[/itex] and [itex]\odot[/itex], of [itex]F[/itex] on [itex]V[/itex] such that [itex]V[/itex] is an [itex]F[/itex]-module.

A usual way to solve this is to take any vector space over a field with a non-trivial automorphism group, and define [itex]r\odot \mu[/itex] to be [itex]f(r)\cdot \mu[/itex] for [itex]f\in \text{Aut}(F), f\neq \iota[/itex].

My question is: is this essentially the only way? Given two different actions of [itex]F[/itex] on [itex]V[/itex], can we construct a non-trivial automorphism of [itex]F[/itex]?

Or, a weaker result: can we show that a prime field cannot act in two different ways on a module?
 
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We always have the trivial operation: ##F.V \equiv 0##.
Another example are direct versus semidirect products. And if the automorphism group is large enough, we can have different conjugations.

And ##D_{12} \cong V_4 \ltimes \mathbb{Z}_3 \cong D_6 \times \mathbb{Z}_2## might provide an example as we have two copies of ##\mathbb{Z}_2## here with a different operation on the rest.
 

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