Algebraic Number Theory, Summer semester 2020

Lecturer: Dr. Andrey Soldatenkov

Exams:
First date: Friday 24.07.20, 9:00 - 17:00
Second date: Friday 09.10.20, 9:00 - 17:00

The exams will be in the form of "Take Home Klausur": problems will be published in the morning on the Moodle page of the course and participants will have time until the evening to submit their solutions via Moodle or by e-mail (scans or readable photos of handwritten solutions will be acceptable; you do not need to typeset your solutions in LaTeX). Please register for the exam in AGNES.

Lectures: Monday 09:00 - 11:00, 11:00 - 13:00,

Online lectures in Zoom will start on 20.04.20. To get access to the online lectures you need to enrol on the Moodle course. The enrolment key will be sent out by e-mail to all students registered for the course in AGNES. You will find a link to the Zoom meetings on the right hand side of the Moodle page of the course. You can contact me by e-mail in case of any problems.

Exercise sessions (by Jan Hesmert, e-mail: jan.hesmert at hu-berlin.de): Wednesday 11:00 - 13:00

The exercise sessions will also take place in Zoom starting on 22.04.20

Announcement

We will give an introduction to the methods of algebraic number theory. Among the topics to be discussed: number fields and their rings of integers, Dedekind rings, ideal classes and the unit theorem, valuations and completions, field extensions and ramification.

Prerequisites. Standard undergraduate algebra (basic properties of the ring of integers and its quotient rings; groups; polynomial rings; finitely generated abelian groups). We will also assume familiarity with Galois theory, but all necessary facts will be recalled (mostly without proofs).

Lecture notes

20.04.20:
Lecture 1: introduction, the ring of Gaussian integers, representation of primes as sums of two squares
Lecture 2: reminder on Galois theory
27.04.20:
Lecture 3: trace and norm in field extensions
Lecture 4: algebraic integers, integral extensions of rings
04.05.20:
Lecture 5: lattices in vector spaces, algebraic integers form a lattice, discriminant of a number field
Lecture 6: ideals in the rings of algebraic integers, the spectrum of a ring, Dedekind domains
11.05.20:
Lecture 7: Noetherian rings, Hilbert's basis theorem
Lecture 8: fractional ideals, decomposition of ideals in Dedekind domains
18.05.20:
Lecture 9: ideal class group of a number field, norms of ideals + examples of computations in Sage
Lecture 10: volumes of lattices and norms of ideals
25.05.20:
Lecture 11: finiteness of the ideal class group + more examples in Sage
Lecture 12: Minkowski's bound, examples of quadratic fields
8.06.20:
Lecture 13: Dirichlet's unit theorem
Lecture 14: units in quadratic fields, decomposition of primes under field extensions, ramification
15.06.20:
Lecture 15: localization of rings
Lecture 16: discrete valuation rings
22.06.20:
Lecture 17: decomposition of primes in Galois extensions, decomposition group, Frobenius elements
Lecture 18: cyclotomic fields, discriminants and ramification
29.06.20:
Lecture 19: more about cyclotomic fields
Lecture 20: absolute values and completions
6.07.20:
Lecture 21: Archimedian and non-Archimedian absolute values on number fields
Lecture 22: complete discrete valuation rings
13.07.20:
Lecture 23: Hensel's lemma, roots of unity in the ring of p-adic integers

Exercise sheets

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12

Literature