Geometry and Topology

Temple University's Geometry/Topology research group specializes in connections between low-dimensional topology, hyperbolic geometry, arithmetic groups, and geometric group theory.

Click on picture for details.

Research Profile

The Geometry/Topology group is active in a variety of research areas including:

  • hyperbolic geometry: Kleinian groups, Teichmüller theory
  • geometric group theory: cubical geometry, hyperbolic groups and generalizations, mapping class groups
  • dynamics: homogenous dynamics, random walks, flows on 3-manifolds
  • low dimensional topology: knot theory, triangulations
  • arithmetic manifolds


The Geometry/Topology group organizes the following events:

  • Annual Graduate Student Conference in Algebra, Geometry and Topology
  • Monthly PATCH seminar, jointly with the University of Pennsylvania, Bryn Mawr College and Haverford College
  • Several weekly department seminars
  • Summer reading groups

Postdoctoral Program Alumni

Christopher Atkinson, Research Assistant Professor (2009-12)

Chris Atkinson studies low-dimensional geometry and topology. His research provides an algorithmic method for estimating the volume of any non-obtuse hyperbolic polyhedron in terms of the combinatorics of its 1-skeleton. He is currently studying realization spaces and degenerations of hyperbolic polyhedra as well as questions related to the interaction between the geometry and topology of hyperbolic 3-orbifolds.

Akinson received his Ph.D. at the University of Illinois-Chicago, as a student of Ian Agol. He is currently an Associate Professor at the University of Minnesota, Morris.

Edgar Bering, Research Assistant Professor (2017-20)

Edgar Bering's research interests are broadly in the area of geometric group theory. Specifically he is interested in the geometry of free groups as reflected by their (outer) automorphisms, the analogy between the resulting structure theory and surface theory, and applications of the theory throughout low dimensional topology.

Bering received his Ph.D. at the University of Illinois-Chicago, as a student of Marc Culler. He is currently a postdoctoral fellow at the Technion.

Ser-Wei Fu, Research Assistant Professor (2014-17)

Fu studies various interplay between hyperbolic geometry, geometric group theory, low-dimensional topology, and dynamical systems. These topics are tied together through the study of closed curves on a surface. Fu is particularly interested in flat metrics on surfaces and Teichmuller dynamics.

Fu received his Ph.D. at the University of Illinois Urbana-Champaign, as a student of Chris Leininger. He is currently a postdoc at National Taiwan University.

Justin Malestein, Research Assistant Professor (2009-12)

Justin Malestein's research interests lie in low-dimensional (2 or 3) geometry/topology, rigidity theory, and applied math. He does research relating algebraic properties of mapping classes of surfaces and curves on surfaces to their topological/combinatorial properties. He is also currently researching combinatorial aspects of rigidity theory, inorganic crystals known as zeolites and the relation between the two.

Malestein received his Ph.D. at the University of Chicago, as a student of Benson Farb. He is currently an Assistant Professor at the University of Oklahoma.

Kei Nakamura, Research Assistant Professor (2009-13)

Kei Nakamura's research interests are in low-dimensional topology and geometric group theory. These two closely related areas have always enriched each other. Nakamura primarily focuses on questions regarding 3-manifolds and their Heegaard splittings, knot theory, hyperbolic geometry, hyperbolic and relatively hyperbolic groups, mapping class groups, and the interplay between them.

Nakamura received his Ph.D. at the University of California, Davis as a student of Joel Hass. He is currently a Research Associate at Rutgers University.

Brian Rushton, Research Assistant Professor (2012-15)

Brian Rushton studies geometric group theory and low-dimensional topology, focusing on finite subdivision rules for 3-manifolds. If we lived in a small 3-manifold, we would see ourselves reflected across the sky in a fractal-like pattern. Finite subdivision rules give a formula for such a pattern, and they are used to translate combinatorial data into analytic data.

Rushton received his Ph.D. at Brigham Young University, as a student of James Cannon. Following his time at Temple, Rushton became an Assistant Professor at Brigham Young University, Hawaii.

Louis Theran, Research Assistant Professor (2009-11)

Louis Theran's research interests relate to combinatorial rigidity, which relates the geometric properties objects defined by geometric constraints (e.g., scaffolds) to the combinatorial properties of their incidence structures. Along the way, algorithms, tree decompositions of graphs, and random graphs all come up. At the moment, Louis has been working questions arising in the study of zeolites with Igor Rivin. In the distant past, Louis worked at the OSF research center's web group and later the Nokia Research Center; then he decided to go to college.

Theran received his Ph.D. at the Univeristy of Massachusetts, Amherst, as a student of Ileana Streinu. He is currently a Lecturer at the University of St Andrews.

Graduate Student Alumni

Dianbin Bao

Dianbin Bao studies identities between Hecke eigenforms, and their arithmetic consequences, for congruence subgroups of the modular group. His thesis advisor was Matthew Stover.

First position after graduation: Research postdoc at Notre Dame. Current position: Instructor at Penn State Abington.

Michael Dobbins

Michael Dobbins' primary research interests are discrete geometry, convexity, combinatorics, topology, and foundations. His preferred programming language is Haskell.

Dobbins received his Ph.D. in 2011, as a student of Igor Rivin. He is currently an Assistant Professor at Binghamton University.

Christian Millichap

Christian Millichap is pursuing research in the area of low-dimensional topology and hyperbolic geometry. He is interested in the properties of hyperbolic 3-manifolds that have a number of geometric invariants in common, but are non-isometric. In particular, he studies how many hyperbolic 3-manifolds can have the same volume or the same geodesic lengths, the types of constructions used to build such geometrically similar hyperbolic 3-manifolds, and relations between geometrically similar hyperbolic 3-manifolds and commensurability.

Millichap received his Ph.D. in 2015, as a student of Dave Futer. He is currently an Assistant Professor at Furman College.

Tim Morris

Tim Morris studies character varieties of 3-manifold groups and knot theory, including topological and geometric properties of finite covers of knot complements. His thesis advisor was Matthew Stover.

First position: Visiting Assistant Professor, New York Institute of Technology.

Thomas Ng

Thomas Ng pursued dissertation research on the interplay between geometric group theory and low-dimensional topology. He is interested in algorithmic properties of groups that arise in the study of surfaces and 3-manifolds from the coarse geometry of their actions on various combinatorial objects and complexes. His thesis advisor was Dave Futer.

First position: Postdoctoral fellow at the Technion.

William Worden

William Worden pursued dissertation research on the hyperbolic geometry of knot complements and other 3-manifolds. He is interested in canonical triangulations of knot complements, and in particular the link between combinatorial/ geometric properties of the triangulation, and combinatorial properties of the knot. He is also interested in surface homeomorphisms, veering triangulations of punctured surface bundles (as described by Ian Agol), and commensurability of 3-manifolds. His thesis advisor was Dave Futer.

First position: G.C. Evans Instructor at Rice University.

Graduate Courses in Geometry and Topology

Math 8061-62: Smooth Manifolds

This course will be an introduction to the geometry and topology of smooth manifolds. We will begin the fall semester with the definitions: what does it mean for a space to (smoothly) look just like Rn? We will go on to study vector fields, differential forms (a way to take derivatives and integrals on a manifold), and Riemannian metrics.

In the spring semester, we'll study the interplay between the geometry of a manifold and certain ideas from algebraic topology. We will review the idea of the fundamental group and introduce homology - and then relate these algebraic notions to the underlying geometry. If time permits, we will talk a bit about hyperbolic manifolds - a family of manifolds where the interplay between topology and geometry is particularly strong and beautiful.

The textbooks for this course are Introduction to Smooth Manifolds by John Lee and Algebraic Topology by Allen Hatcher.

Math 9021: Riemannian Geometry

The main goal of this one-semester course is to provide a solid introduction to the two central concepts of Riemannian Geometry, namely, geodesics and curvature and their relationship. After taking this course, students will have an intimate acquaintance with the tools and concepts that are needed for pursuing research in Riemannian Geometry or applying its ideas to other fields of mathematics such as analysis, topology, and algebraic geometry.

Math 9005: Graph Theory

This course will be an introduction to graph theory. Some of the topics covered will be:

  • Trees, connectivity, and matroids
  • Matchings and 2-factorizations
  • Planarity, duality, and graph drawing
  • Random graphs

We'll be using Graph Theory by Diestel as the main course text, with supplements from more specialized monographs (e.g., Matching Theory by Lovasz & Plummer, Matroid Theory by Oxley) as necessary.

Math 9023-24: Knot Theory and Low Dimensional Topology

This course will survey the modern theory of knots, coming at it from several very distinct points of view. We will start at the beginning with projection diagrams and the tabulation problem. We will proceed to several classical polynomial invariants, which can be constructed via the combinatorics of diagrams, via representation theory, or via the topology of the knot complement. We will touch on braid groups and mapping class groups, and use these groups to show that every (closed, orientable) 3-manifold can be constructed via knots. Finally, we will use these constructions to gain a glimpse of several skein-theoretic and quantum invariants of 3-manifolds.

Textbooks for this course include An Introduction to Knot Theory, by W.B. Raymond Lickorish, and Knots, Links, Brads, and 3-Manifolds, by V.V. Prasolov and A.B. Sossinsky.

Math 9061-62: Lie Groups

This will be a course on the basic theory of Lie groups and Lie algebras, with a geometric point of view. We will cover the structure theory and classification, along with the rich geometry associated with these groups via the geometry of symmetric spaces. In particular, we will study the classification of semisimple Lie groups and apply that to classify low-dimensional homogeneous spaces, which are spaces that `look the same' at every point. The course will use some Riemannian geometry, but will also introduce the necessary concepts as we go along.

Math 9210: Mapping Class Groups and Braid Groups

This course will focus on the symmetry groups of manifolds and cell complexes. We will look at both the geometric and algebraic properties of the mapping class group, which can roughly be thought of as the group of symmetries of a surface. One of the ways in which we will study the group is by designing a certain cell complex on which it acts by isometries. This principle has wide generalizations: one can derive a great deal of information about a group by constructing a geometric object for the group to act on.

In the spring semester, we will focus our attention on the braid groups, which are a special class of mapping class groups. In particular, we will study the representation theory of these groups, with connections to invariants of knots and links.

MATH 9073: Geometric Group Theory

This semester-long course will survey the rapidly expanding field of geometric group theory, focusing on the role played by negative curvature. We will begin with classical combinatorial techniques used to construct and study infinite discrete groups. After introducing basic concepts in coarse geometry, we will turn our attention to Gromov's notion of hyperbolic groups. In addition to studying geometric, algebraic, and algorithmic properties of these groups, we will keep an eye towards several generalizations of hyperbolicity that have recently played a large role in understanding many geometrically significant groups. As examples, we will also touch on the study of mapping class groups, outer automorphism groups of free groups, and cubical groups.

Math 8062: Hyperbolic Manifolds

This course will be an introduction to discrete groups and hyperbolic manifolds via explicit topological constructions. We will begin with the basics of discrete groups of isometries and hyperbolic 2-manifolds. Then we will consider geometric structures on knot complements, Thurston's hyperbolic Dehn surgery theorem, and related explicit constructions of hyperbolic 3-manifolds.