Winter 2013, Section 1
Math 776, as the continuation of Math 676 , is a secondsemester
graduate course in algebraic number theory. While Math 676 covered a variety
of basic topics, Math 776 will focus on a single topic: Class Field Theory,
the study of abelian extensions of number fields.
Course details
Time: Mon, Wed, Fri 1:10pm2:00pm
Place: 2866 East Hall
First meeting: Wednesday, January 9, 2013
About the instructor
Jeffrey Lagarias
Email: lagarias@umich.edu
Web: http://www.math.lsa.umich.edu/~lagarias/m776.html
Office: 3086 East Hall
Office Phone: 7631186
Office Hours: MWF 2:1103:00, or by appointment!
Course description
Class field theory, the study of abelian extensions of number fields,
was a crowning achievement of number theory in the first half of the 20th
century. It brings together, in a unified fashion, the quadratic and higher
reciprocity laws of Gauss, Legendre et al, and vastly generalizes them.
Some of its consequences (e.g., the Chebotarev density theorem) apply
even to nonabelian extensions.
Our approach in this course will be to begin with review and the
KroneckerWeber theorem. Then we cover
the formulations of
the statements of global class field theory, for number fields,
and local class field theory, for padic fields.
Textbooks
We will not follow a single text consistently.
The primary text will be Serge Lang,
Algebraic Number Theory, 2nd Edition SpringerVerlag 1994.
This text seems rather dry and unmotivated, but it covers the
right things on the analytic side.
I hope to supply sufficient motivation in class.
A second good source is J.S. Milne's course notes
on class field theory, which can be downloaded
here.
A classical source is G.Janusz
Algebraic Number Fields, 2nd Edition (AMS 2005)
A very good modern source is Neukirch's
Algebraic Number Theory (SpringerVerlag 1999).
Students are encouraged to have at least
one of these last two sources available.I will point out where
the material we cover
in class is covered in both.
Other good references:
 Cassels and Frohlich, Algebraic Number Theory (excellent, but
out of print)
 Serre, Local Fields (for local class field theory)

Washington, Introduction to Cyclotomic Fields (for KroneckerWeber,
and some applications)
Prerequisites
Math 676 or equivalent. Graduate coursework in algebra
is also recommended. If you are unsure how your
background matches these prerequisites, see me.
Homework/Exams
There will be problem sets approximately biweekly for most of the semester.
There will be no final exam; instead, students will submit a final paper
on a topic not covered during the course.
Some spossible topics are listed
below (under "Additional Topics"); feel free to come up with others!
Possible Topics

Abelian extensions of the rationals: the KroneckerWeber theorem
(Milne, I.4; Washington, Chapter 14)

Statements of results: classical form
(Milne, V.1V.3)

Some applications of class field theory

Statements of results: modern (adelic) form

Group cohomology (Milne, II)

Local class field theory (Milne, I.1 and III; Neukirch, IV and V)

Proofs of the results of class field theory (Milne, VII; Neukirch, IV and VI)

Additional topics (see below) if time permits.
Additional topics
These are topics not covered in the course, but
accessible once we have completed the planned syllabus. In particular,
these topics would be suitable for a final paper. This list is subject to
change as the semester progresses.
 The LubinTate approach to local class field theory (Milne, I.2)
 Brauer groups (Milne, IV)
 Quadratic forms over number fields (Milne, IV)
 The Carlitz module and class field theory for function fields (David Hayes, A brief introduction to Drinfeld modules, in The Arithmetic
of Function Fields)
 Serre's approach to class field theory for function fields (Serre,
Algebraic Groups and Class Fields)
 Class field towers: the GolodShafarevich inequality (CasselsFrohlich)
 Complex multiplication: explicit class field theory for imaginary
quadratic fields (Neukirch, VI.6)
 Zeta functions and number fields (Neukirch, VII)
 Arakelov divisors, notion of genus for number field (Neukirch, III,
see me please)
Jeff Lagarias
(lagarias(at)umich.edu)
Homework Assignments:
Homework 0
(due Monday January 14 )
Homework 1
(due Monday January 28)
Homework 2
(due Monday February 18)
Homework 3
(due Wednesday March 13)
Homework 4
(due Monday April 8)