MTH 783: Character varieties and 3-dimensional topology

University of Miami, Fall 2025

Instructor: Christopher Scaduto
Email: c.scaduto @ math.miami.edu
Office: Ungar 525
Office hours: 12:30-1:30 Thursday, or by appointment
Time and Location: TuTh 11AM - 12:15PM, Ungar 411

Course syllabus can be found here.

There is no single textbook for the course. References for some material covered:

[KM] Kronheimer and Mrowka, Dehn surgery, the fundamental group and SU(2): pdf

Course Schedule

Date Lecture Content
8/19/25 Introduction. Dehn Surgery on knots.
Saveliev, Lectures on the Topology of 3-Manifolds: Lecture 2 §2.1-2.3 (see also Lecture 1 for some relevant background)
Further reading: Gordon, Dehn surgery and 3-Manifolds (2006). Many examples and exercises. (Not up to date, though.)
8/21/25 Wirtinger presentations. Fundamental groups of surgeries.
Rolfsen, Knots and Links: The Wirtinger Presentation §3.D
8/26/25 SU(2) and quaternions. Representations spaces and conjugation action.
Saveliev, Lectures on the Topology of 3-Manifolds: Lecture 13
house notes: SU(2) as unit quaternions
8/28/25 Stabilizer types of representations. The reducible part of the character variety.
house notes: Stablizers and orbits, and the reducible characters
9/2/25 SU(2) character varieties of knots. Example computations. The pillowcase.
Kirk, SU(2) Representation Varieties of 3-manifolds, Gauge Theory Invariants, and Surgery on Knots: pdf Ch.1
9/4/25 Torus knots. Herald's Theorem on the structure of the SU(2) character variety (intro).
Klassen, Representations of knot groups in SU(2): pdf IA, IB
9/9/25 Perturbations, Herald's Theorem. Character varieties, amalgamated groups, and Dehn surgery.
Herald, Legendrian cobordism and Chern-Simons theory on 3-manifolds: link
Herald, Kirk, Holonomy perturbations in a cylinder... link, see especially §2
9/11/25 Understanding Dehn surgery in the pillowcase. Proving first cases of Thm 1 from from [KM]
Kirk paper above, KM paper above
9/16/25 Proof of Thm 1 from [KM]. Perturbations in a thickened torus.
KM paper above; Herald-Kirk paper above does more involved perturbations
9/18/25 Local structure of representation spaces. Zariski tangent spaces. Group cohomology.
Saveliev, Lectures on the Topology of 3-Manifolds: Lecture 15
Weil, Remarks on the cohomology of groups: pdf
9/23/25 Homology with local coefficients. Zariski tangent space computations for the pillowcase.
Kirk paper above, Hatcher Algebraic Topology § 3.H
9/25/25 Local structure at a reducible, and relation to the Alexander polynomial.
Lickorish, An introduction to Knot Theory Ch 6
Milnor, Infinite cyclic coverings §1-2
9/30/25
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10/2/25
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