Samantha Allen

Research Interests

My research interests lie in the field of low-dimensional topology, the study of manifolds in dimensions up to four. More specifically, I study knot theory in dimensions 3 and 4 and I am particularly interested in using knot invariants arising from Heegaard Floer theory to study knot concordance, problems related to unknotting operations, and other knot-theoretic problems.

Put simply, a mathematical knot is a knotted up loop in 3-dimensional space. Two knots are called equivalent if one can be deformed to another via an ambient isotopy (i.e. without breaking the loop or passing in through itself). A knot invariant is a function whose input is a knot and whose output does not change under ambient isotopy. In other words, a knot invariant sends equivalent knots to equivalent outputs. Knot invariants come in many different forms (binary, integer, function, polynomial, group, etc.) and arise in many different ways (diagrammatic, associated manifolds, etc.).

Knots are often considered up to concordance. Concordance is an equivalence relation on the set of knots, and the equivalence classes form a group. Many (but not all) knot invariants are also concordance invariants.

Publications and Preprints

(Euler number, first Betti number)

Do Link Polynomials Detect Causality In Globally Hyperbolic Spacetimes? Joint with undergraduate Jacob H. Swenberg.
J. Math. Phys. 62 (2021), no. 3, 032503. arXiv.

Let X be a (2+1)-dimensional globally hyperbolic spacetime with a Cauchy surface whose universal cover is homeomorphic to R^2. We provide empirical evidence suggesting that the Jones polynomial detects causality in X. Specifically, we exhibit an infinite family of links that are distinguished from the connected sum of two Hopf links by their Jones polynomials. We introduce a new invariant of certain tangles related to the Conway polynomial, and suggest that the Conway polynomial does not detect causality in the scenario described by producing an explicit link. The Conway polynomial fails to distinguish this link from the connected sum of two Hopf links.

(The paper above is the result of an undergraduate research project with undergraduate Jacob Swenberg, which I co-mentored with Ina Petkova and Vladimir Chernov.)


A 3-component link

Nonorientable surfaces bounded by knots: a geography problem. Submitted for publication. arXiv.

The nonorientable 4-genus is an invariant of knots which has been studied by many authors, including Gilmer and Livingston, Batson, and Ozsvath, Stipsicz, and Szabo. Given a nonorientable surface with boundary a knot, an analysis of the existing methods for bounding and computing the nonorientable 4-genus reveals relationships between the first Betti number and the normal Euler class of the surface. This relationship yields a geography problem: given a knot K, what is the set of realizable pairs (e(F), b_1(F)) where F is a nonorientable surface bounded by K?


The trefoil with an untwisting linked unknot.

Unknotting with a single twist. Joint with Charles Livingston. To appear in L'Enseignement Mathematique. arXiv.

Given a knot K in S^3, is it possible to unknot it by performing a single twist, and if so, what are the possible linking numbers of such a twist? We develop obstructions to unknotting using a twist of a specified linking number. The obstructions we describe are built using classical knot invariants, Casson-Gordon invariants, and Heegaard Floer theory.

See two virtual talks on this paper:


CFK^\infty(T(5,6))

Concordances from differences of torus knots to L-space knots.
Proc. Amer. Math. Soc. 148 (2020), no.4, 1815-1827. arXiv.

It is known that connected sums of positive torus knots are not concordant to L-space knots. Here we consider differences of torus knots. The main result states that the subgroup of the concordance group generated by two positive torus knots contains no nontrivial L-space knots other than the torus knots themselves. Generalizations to subgroups generated by more than two torus knots are also considered.


CFK^\infty(T(2,5)#T(5,6))

Using secondary Upsilon invariants to rule out stable equivalence of knot complexes.
Algebr. Geom. Topol. 20 (2020), no. 1, 29-48. arXiv.

Two Heegaard Floer knot complexes are called stably equivalent if an acyclic complex can be added to each complex to make them filtered chain homotopy equivalent. Hom showed that if two knots are concordant, then their knot complexes are stably equivalent. Invariants of stable equivalence include the concordance invariants tau, epsilon, and Upsilon. Feller and Krcatovich gave a relationship between the Upsilon invariants of torus knots. We use secondary Upsilon invariants defined by Kim and Livingston to show that these relations do not extend to stable equivalence.