# Difference between revisions of "Rational group"

## Contents

This article defines a term that has been used or referenced in a journal article or standard publication, but may not be generally accepted by the mathematical community as a standard term.[SHOW MORE]
This article defines a group property: a property that can be evaluated to true/false for any given group, invariant under isomorphism
View a complete list of group properties
VIEW RELATED: Group property implications | Group property non-implications |Group metaproperty satisfactions | Group metaproperty dissatisfactions | Group property satisfactions | Group property dissatisfactions
This term is related to: linear representation theory
View other terms related to linear representation theory | View facts related to linear representation theory

## Definition

A group is termed a rational group if it satisfies the following equivalent conditions:

1. Given any two elements of the group that generate the same cyclic subgroup, the two elements are conjugate in the group. An element with the property that it is conjugate to any other element that generates the same cyclic subgroup is termed a rational element. A rational group can thus be defined as a group in which all elements are rational elements.
2. Every cyclic subgroup of the group is a fully normalized subgroup of the group.
3. For any element of finite order, if $m$ is relatively prime to the order of an element, then the element and its $m^{th}$ power are conjugate. For any element of infinite order, the element and its inverse must be conjugate.
4. (If the group is finite): If $m$ is relatively prime to the order of the group, then any element and its $m^{th}$ power are conjugate.
5. (If the group is finite): Every linear representation of the group over complex numbers has a rational-valued character.
6. (If the group is finite): Every linear representation of the group over complex numbers has an integer-valued character.
7. (If the group is finite): Every irreducible linear representation of the group over the complex numbers has a rational-valued character.
8. (If the group is finite): Every irreducible linear representation of the group over complex numbers has an integer-valued character.

## Relation with other properties

### Stronger properties

Property Meaning Proof of implication Proof of strictness (reverse implication failure) Intermediate notions
rational-representation group (also called strongly rational group) the field of rational numbers is a splitting field rational-representation implies rational rational not implies rational-representation |FULL LIST, MORE INFO
group with two conjugacy classes

### Weaker properties

Property Meaning Proof of implication Proof of strictness (reverse implication failure) Intermediate notions
group in which any two elements generating the same cyclic subgroup are automorphic if two elements generate the same cyclic subgroup, there is an automorphism of the whole group sending one to the other. (follows from the fact that conjugations are inner automorphisms) all abelian groups that are not elementary abelian 2-groups give examples
ambivalent group every element is conjugate to its inverse rational implies ambivalent ambivalent not implies rational |FULL LIST, MORE INFO
group in which every element is automorphic to its inverse Ambivalent group, Group in which any two elements generating the same cyclic subgroup are automorphic|FULL LIST, MORE INFO

## Metaproperties

Metaproperty Satisfied? Proof Statement with symbols
direct product-closed group property Yes rationality is direct product-closed PLACEHOLDER FOR INFORMATION TO BE FILLED IN: [SHOW MORE]
quotient-closed group property Yes rationality is quotient-closed If $G$ is a rational group and $N$ is a normal subgroup of $G$, then the quotient group $G/N$ is also a rational group.
subgroup-closed group property No rationality is not subgroup-closed It is possible to have a rational group $G$ and a subgroup $H$ of $G$ that is not rational.