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\begin{document}

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\section*{class field theory}

\hypertarget{context}{}\subsubsection*{{Context}}\label{context}

\hypertarget{arithmetic_geometry}{}\paragraph*{{Arithmetic geometry}}\label{arithmetic_geometry}

[[!include arithmetic geometry - contents]]

\hypertarget{contents}{}\section*{{Contents}}\label{contents}

\noindent\hyperlink{idea}{Idea}\dotfill \pageref*{idea} \linebreak
\noindent\hyperlink{related_concepts}{Related concepts}\dotfill \pageref*{related_concepts} \linebreak
\noindent\hyperlink{references}{References}\dotfill \pageref*{references} \linebreak


\hypertarget{idea}{}\subsection*{{Idea}}\label{idea}

\textbf{Class field theory} studies finite-dimensional abelian [[field extensions]] of [[number fields]] and of [[function fields]], hence of [[global fields]] by relating them to the [[idele class group]].

Class field theory clarifies the origin of various [[reciprocity]] laws in [[number theory]]. The basic (one dimensional) class field theory stems from the ideas of Kronecker and Weber, and results of Hilbert soon after them. Main results of the theory belong to the first half of the 20th century (Hilbert, Artin, Tate, Hasse\ldots{}) and are quite different for the [[local field]] from the [[global field]] case. One of the basic objects the class group, is related to the [[Picard group]] in algebraic geometry. Generalizations for higher dimensional fields came later under now active higher class field theory, which is usually formulated in terms of algebraic K-theory and is closely related to deep questions of algebraic geometry (Par\v{s}in, Tate, Kato, Saito etc.).

Given an algebraic [[number field]] $k$ one defines a (congruence divisor) class field group $A/H$ in $k$; according to Weber

\begin{quote}%
An algebraic extension $K/k$ is called a \textbf{class field} to $A/H$, if exactly those prime divisors in $k$ of first degree which belong to the principal class $H$ split completely in $K$


\end{quote}
Some of the basic results of the class field theory are the Artin reciprocity theorem, existence theorem, uniqueness theorem, ordering theorem, Weber isomorphy theorem and the decomposition law of class field theory.

\hypertarget{related_concepts}{}\subsection*{{Related concepts}}\label{related_concepts}

\begin{itemize}%
\item [[Langlands correspondence]]


\item [[geometric class field theory]]


\item [[Artin reciprocity law]]



\end{itemize}
\hypertarget{references}{}\subsection*{{References}}\label{references}

\begin{itemize}%
\item A. Fr\"o{}hlich, J. W. S. Cassels (editors), \emph{Algebraic number theory}, Acad. Press 1967, with many reprints; Fr\"o{}hlich, Cassels, Birch, Atiyah, Wall, Gruenberg, Serre, Tate, Heilbronn, Rouqette, Kneser, Hasse, Swinerton-Dyer, Hoechsmann, systematic lecture notes from the instructional conference at Univ. of Sussex, Brighton, Sep. 1-17, 1965.


\item Albrecht Fr\"o{}hlich, Martin J. Taylor, \emph{Algebraic number theory}, Cambridge Studies in Advanced Mathematics 27, 1993


\item wikipedia \href{http://en.wikipedia.org/wiki/Class_field_theory}{class field theory}


\item A. N. Par\v{s}in A. N. Local class field theory, Trudy Mat. Inst. Steklov \textbf{165} 1984; \emph{Galois cohomology and Brauer group of local fields}, Trudy Mat. Inst. Steklov \textbf{183}, 1984.



\end{itemize}
The following survey of Connes-Marcolli work has a quick introduction to algebraic number theory including basic notions of CFT

\begin{itemize}%
\item P. Almeida, \emph{Noncommutative geometry and arithmetics}, Russian Journal of Mathematical Physics 16, No. 3, 2009, pp. 350--362, \href{http://dx.doi.org/10.1134/S1061920809030030}{doi}, see also nLab:arithmetic and noncommutative geometry

\end{itemize}
The following article sketches the geometric intuition behind the reciprocity laws as the relation between two approaches to the maximal abelian quotient of the fundamental group, mimicking the ideas of Galois theory

\begin{itemize}%
\item Alexander Schmidt, \emph{Higher dimensional class field theory from a topological point of view}, \href{http://www.mathi.uni-heidelberg.de/~schmidt/papers/schmidt21-en.html}{page}

\end{itemize}
The following 2 articles make parallel between some notions of [[QFT]] and of number theory and in particular about the analogy between the [[Weil reciprocity law]] for [[function field]]s and the Takahashi-Ward identities of field theory:

\begin{itemize}%
\item [[Leon Takhtajan]], \emph{Quantum field theories on algebraic curves and A. Weil reciprocity law}, \href{http://arxiv.org/abs/0812.0169}{arxiv/0812.0169}; \emph{Quantum field theories on an algebraic curve}, \href{http://www.math.sunysb.edu/~leontak/Takhtajan-00.pdf}{pdf}, 2000

\end{itemize}
Some history is in

\begin{itemize}%
\item James W. Cogdell, \emph{L-functions and non-abelian class eld theory, from Artin to Langlands}, 2012 (\href{https://people.math.osu.edu/cogdell.1/Artin-www.pdf}{pdf})

\end{itemize}


\end{document}