Let $L$ be a finite extension of the $p$-adic field $\mathbb{Q}_p$ with ring of integers $\mathcal{O}_K$ with uniformizer $\pi$. Let us consider the polynomial ring $L[x_1,x_2,\dotsc,x_l]$ in $l$-variables and $f_1, f_2, \dotsc, f_m \in L[x_1, \dotsc, x_l]$.
Let $S$ be the set of simultaneous zeros of the following system \begin{align} f_1(x_1,\dotsc,x_l) & {}=0 \\ \vdots & \\ f_m(x_1, \dotsc,x_l) & {}=0. \end{align} Then, clearly every element in $S$ is a point in an affine $l$-space over some field extension of $L$. So the coordinates of each points in $S$ generate a field extension. i.e., consider the field extension $L(S)$ obtained by adjoining the coordinates of each solution to $S$. So it looks like $L(S)$ is a subfield of $\bar L$.
Questions:
Is (or when is) the extension $L(S)/L$ Galois?
When is $L(S)/L$ totally ramified?
My Effort:
- $L(S)$ is an algebraic extension of $L$ because its elements are algebraic over $L$. In this multivariable case, we don't need separability of the roots/solutions because we are taking the coordinates only. Also two solutions $(x_1, \dotsc,x_l)$ and $(x_1',\dotsc, x_l')$ may have some common coordinates, say, $x_i=x_i'$ but this doesn't affect because both give the same extension, so we will take just one of the coordinates.
Let $L'$ be the Galois closure of $L(S)$ over $L$ i.e, the smallest field containing $L(S)$ that is Galois over $L$. Take any $\sigma \in \operatorname{Gal}(L'/L)$ and a solution $s \in S$, then its Galois conjugate $\sigma(s)$ is also a solution i.e., $\sigma(s) \in S$. So $\sigma(s)=t$ for some $t \in S$. So by restricting the domain of $\sigma$ to $L(S)$, we have $$\sigma(L(S)) \subset L(S).$$ Next, since $\sigma$ induces a permutation on $S$, then for each $\alpha \in L(S)$, $\sigma^{-1}(\alpha)=\beta$ for some $\beta \in L(S)$. So $\alpha=\sigma(\beta)$ and so we have $$L(S) \subset \sigma(L(S)).$$
Therefore, $\sigma(L(S))=L(S)$. Thus each $\sigma\rvert_{L(S)}$ is an automorphism. So it seems that $L(S)$ is Galois over $L$.
Am I correct? Am I missing something?
Any discussion please.
proper
. But in Chat section, as you said, $L(S)=\bar L$ was in previous setting, slightly different. I am not sure whether in the current setting $L(S)$ is equal to $\bar L$ or not. Second, regarding the level of the question, I want to define a map $Gal(L(S)/L) \to (\mathcal{O}_K/\pi^n \mathcal{O}_K)^{\times}, \ n \geq 1$, once I know $Gal(L(S)/L)$ is Galois. Any help here ? $\endgroup$