Gregory A. Kelsey

Gregory Kelsey


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Research Interests

  • Geometric and combinatorial group theory, especially problems related to Grigorchuk's group, iterated monodromy groups of complex dynamical systems, and other self-similar groups.

  • The scholarship of teaching and learning mathematics at the undergraduate level, especially problems related to higher-order thinking skills, knowledge retention, and motivation.

Research Statement

I find that mathematics expresses itself most beautifully in the interplay between different branches of the field. By this, I mean that I find most aesthetically pleasing any arguments that leverage multiple interpretations of particular mathematical objects to prove deep conclusions. To me, high school students receive their best taste of pure mathematics when they employ both algebraic and geometric properties to solve problems (with linear functions, for example). As a geometric group theorist, I study groups by considering their actions on nice geometric spaces; this approach gives me two (or sometimes more) ways of learning about the group, and they usually complement each other well. ... Full document

If you are looking for a more specific example of what I do (with an interactive JavaScript!), you may find this interesting.

Current Projects

  • Topological mating is a procedure by which two topological polynomials are used to produce a Thurston map. Sometimes, mating different pairs of polynomials will result in equivalent Thurston maps. The reason for this phenomenon remains unclear. I am investigating this problem by studying the associated iterated monodromy groups and the inclusions induced by the mating.

  • In the Fall 2010 and Spring 2011 semesters, I will investigate the effectiveness of using wikis to facilitate class projects. I will consider not only the effect wiki technology has on students' mastery of mathematical concepts, but also its effect on affective learning goals, such as students' interest in mathematics and views on mathematics' importance.


  • "Mega-bimodules of topological polynomials: Sub-hyperbolicity and Thurston obstructions"
    My Thesis
    Abstract: In 2006, Bartholdi and Nekrashevych solved a decade-old problem in holomorphic dynamics by creatively applying the theory of self-similar groups. Nekrashevych expanded this work in 2009 to define what we refer to as mega-bimodules which capture the topological data of Hurwitz classes of topological polynomials. He also showed that proving that these mega-bimodules are sub-hyperbolic will have two important implications: that all iterated monodromy groups of topological polynomials are contracting and that the Hubbard-Schleicher spider algorithm for complex polynomials generalizes to topological polynomials. We prove sub-hyperbolicity in the simplest non-trivial case and apply these mega-bimodules to holomorphic dynamics to prove a partial converse to the Berstein-Levy Theorem proved in 1985.

  • "Mapping schemes realizable by obstructed topological polynomials"
    Abstract: In 1985, Levy used a theorem of Berstein to prove that all hyperbolic topological polynomials are equivalent to complex polynomials. We prove a partial converse to the Berstein-Levy Theorem: given post-critical dynamics that are, in a sense, strongly non-hyperbolic, we prove the existence of topological polynomials realizing these post-critical dynamics whiich are not equivalent to any complex polynomial. This proof employs the theory of self-similar groups to demonstrate that a topological polynomial admits an obstruction, and produces a wealth of examples of obstructed topological polynomials.

  • "Group work and self-efficacy in a business calculus class"
    Abstract: In a business calculus course with lecture and discussion sections, TAs ran half the discussion sections in the standard format and half in a group work format. At the beginning and end of the semester, students completed brief surveys indicating their confidence in their ability to perform mathematical procedures and their ability to learn new mathematics. The changes in the reported learning self-efficacy of the students in the group work sections correlated strongly with their final course grades, unlike in the standard sections. This suggests that while group work may not increase students learning self-efficacy, it might improve the accuracy with which students perceive their own abilities.

  • "Wordlength in Alternative Finite Presentations of Thompsons' Group F"
    This was my honors project in mathematics at Bowdoin College, done under the supervision of Jen Taback. I prove that the wordlength of an element of Thompson's group F with respect to the standard finite generating set (which we can compute by a result of Fordham) provides a linear bound on the wordlength of that element with respect to alternative two element generating sets. I then use this result to show that most dead end words with respect to the standard generating set are not dead end words with respect to the "next" natural generating set.

  • "Muddy Children, Temporary Deafness, and the 10,000th Digit of the Square Root of 2: Modeling Knowledge"
    This was my honors project in economics at Bowdoin College, done under the supervision of Dorothea Herreiner. I review some concepts from model theory and logic and discuss how they can be applied to easing the troublesome assumption of complete knowledge that crops up so frequently in game theory.

    Talks and Presentations