Arithmetic Constructions Of Binary Self-Dual Codes

The goal of this thesis is to explore the interplay between binary self-dual codes and the 'etale cohomology of arithmetic schemes. Three constructions of binary self-dual codes with arithmetic origins are proposed and compared: Construction $\Q$, Construction G and the Equivariant Construction. In this thesis, we prove that up to equivalence, all binary self-dual codes of length at least $4$ can be obtained in Construction $\Q$. This inspires a purely combinatorial, non-recursive construction of binary self-dual codes, about which some interesting statistical questions are asked. Concrete examples of each of the three constructions are provided. The search for binary self-dual codes also leads to inspections of the cohomology ``ring" structure of the 'etale sheaf $\mu_2$ on an arithmetic scheme where $2$ is invertible. We study this ring structure of an elliptic curve over a $p$-adic local field, using a technique that is developed in the Equivariant Construction.