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Galois theory, named after Évariste Galois, provides a connection between field theory and group theory. Using Galois theory, certain problems in field theory can be reduced to group theory, which is, in some sense, simpler and better understood.

11 votes

Which groups are Galois over some p-adic field?

I'll upgrade my comment to an answer. Any finite Galois extension of $\mathbb{Q}_l$ of degree coprime to $l$ is tamely ramified. In particular, its Galois group is an extension of two cyclic groups. …
Daniel Loughran's user avatar
11 votes
1 answer
790 views

Cyclic cubic extensions and Kummer theory

The Galois cohomology group $H^1(\mathbb{Q}, \mathbb{Z}/3\mathbb{Z})$ classifies cyclic cubic extensions $K/\mathbb{Q}$ (specifically: the non-trivial elements correspond to Galois cubic field extensi …
Daniel Loughran's user avatar
7 votes
3 answers
845 views

Constructing quintic number fields with certain splitting behaviour

I am looking for number fields $K$ which satisfy the following properties: $[K:\mathbb{Q}]=5$. The Galois closure of $K$ has Galois group $S_5$. For each prime $p$ which ramifies in $K$, there exist …
Daniel Loughran's user avatar
6 votes
Accepted

Minimal fields of isomorphism for varieties

Yes if $K=\mathbb{R}$ for example, but no in general. Namely this fails for curves of genus $1$, over $\mathbb{Q}$, say. Given an elliptic curve $E$ over $\mathbb{Q}$ and a positive integer $d$, a ge …
Daniel Loughran's user avatar
4 votes

Applications of the Galois embedding problem

Shafarevich made heavy use of embedding problems in his resolution of the inverse Galois problem for solvable groups. The (naive) viewpoint is that solving the relevant embedding problems allowed him …
Daniel Loughran's user avatar