18.785
Number Theory I
Dedekind domains, unique factorization of ideals, splitting of primes. Lattice methods, finiteness of the class group, Dirichlet's unit theorem. Local fields, ramification, discriminants. Zeta and L-functions, analytic class number formula. Adeles and ideles. Statements of class field theory and the Chebotarev density theorem.
Fall 2021
Topics
- Absolute Values and Discrete Valuations
- Localization and Dedekind Domains
- Properties of Dedekind Domains and Factorization of Ideals
- Étale Algebras, Norm and Trace
- Dedekind Extensions
- Ideal Norms and the Dedekind-Kummer Theorem
- Galois Extensions, Frobenius Elements, and the Artin Map
- Complete Fields and Valuation Rings
- Local Fields and Hensel’s Lemmas
- Extensions of Complete DVRs
- Totally Ramified Extensions and Krasner’s Lemma
- The Different and the Discriminant
- Global Fields and the Product Formula
- The Geometry of Numbers
- Dirichlet’s Unit Theorem
- Riemann’s Zeta Function and the Prime Number Theorem
- The Functional Equation
- Dirichlet L -functions and Primes in Arithmetic Progressions
- The Analytic Class Number Formula
- The Kronecker-Weber Theorem
- Class Field Theory: Ray Class Groups and Ray Class Fields
- The Main Theorems of Global Class Field Theory
- Tate Cohomology
- Artin Reciprocity in the Unramified Case
- The Ring of Adeles and Strong Approximation
- The Idele Group, Profinite Groups, and Infinite Galois Theory
- Local Class Field Theory
- Global Class Field Theory and the Chebotarev Density Theorem
Readings
- Number theory is a vast subject, and it is good to see it from many different perspectives. Below are a number of standard references that I can recommend. The classic text of Cassels and Frohlich is not “officially” available in online form, but googling “Cassels and Frohlich” will quickly lead you to several scanned versions; alternatively, you can purchase the 2010 reprint by the London Mathematical Society, which corrects most of the errata noted below.
Prerequisites & course information
Prereq: None. Coreq: 18.705 G (Fall) 3-0-9 units
Sources
- Course catalogue ↗2026–2027
- MIT OpenCourseWare ↗Fall 2021
- MIT OCW calendar ↗
- MIT OCW syllabus ↗
- Historical MIT OpenCourseWare offering. Named reading entries and schedule topics are automatically extracted from the linked source pages.