Thesis advisor: John Baldwin / Heegaard Floer homology is a family of invariants in low dimensional topology due originally to Ozsváth-Szabó. We discuss various aspects of Heegaard Floer homology and give several link detection results for versions of Heegaard Floer homology for links. In particular, we show that knot and link Floer homology detect various infinite families of cable links. We also give classification results for the Heegaard Floer theoretic invariants of a type of knot called an “almost L-space knot” and an infinite family of detection results for annular Khovanov homology. / Thesis (PhD) — Boston College, 2023. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Mathematics.

Thesis advisor: John A. Baldwin / Khovanov homology and Heegaard Floer homology have opened new horizons in knot theory and three-manifold topology, respectively. The two invariants have distinct origins, but the Khovanov homology of a link is related to the Heegaard Floer homology of its branched double cover by a spectral sequence constructed by Ozsváth and Szabó. In this thesis, we construct an equivalent spectral sequence with a much more transparent connection to Khovanov homology. This is the first step towards proving Seed and Szabó's conjecture that Szabó's geometric spectral sequence is isomorphic to Ozsváth and Szabó's spectral sequence. These spectral sequences connect information about contact structures contained in each invariant. We construct a braid conjugacy class invariant κ from Khovanov homology by adapting Floer-theoretic tools. There is a related transverse invariant which we conjecture to be effective. The conjugacy class invariant solves the word problem in the braid group among other applications. We have written a computer program to compute the invariant. / Thesis (PhD) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Mathematics.

Since our world is experienced locally in three-dimensional space, students of mathematics struggle to visualize and understand objects which do not fit into three-dimensional space. 3-manifolds are locally three-dimensional, but do not fit into 3-dimensional space and can be very complicated. Twist and bitwist are simple constructions that provide an easy path to both creating and understanding closed, orientable 3-manifolds. By starting with simple face pairings on a 3-ball, a myriad of 3-manifolds can be easily constructed. In fact, all closed, connected, orientable 3-manifolds can be developed in this manner. We call this work a tool kit to emphasize the ease with which 3-manifolds can be developed and understood applying the tools of twist and bitwist construction. We also show how two other methods for developing 3-manifolds–Dehn surgery and Heegaard splitting–are related to the twist and bitwist construction, and how one can transfer from one method to the others. One interesting result is that a simple bitwist construction on a 3-ball produces a group of manifolds called generalized Sieradski manifolds which are shown to be a cyclic branched cover of S^3 over the 2-braid, with the number twists determined by the hemisphere subdivisions. A slight change from bitwist to twist causes the knot to become a generalized figure-eight knot.

This thesis provides a partial classification of all 3-stranded pretzel knots K=P(p,q,r) with unknotting number one. Scharlemann-Thompson, and independently Kobayashi, have completely classified those knots with unknotting number one when p, q, and r are all odd. In the case where p=2m, we use the signature obstruction to greatly limit the number of 3-stranded pretzel knots which may have unknotting number one. In Chapter 3 we use Greene's strengthening of Donaldson's Diagonalization theorem to determine precisely which pretzel knots of the form P(2m,k,-k-2) have unknotting number one, where m is an integer, m>0, and k>0, k odd. In Chapter 4 we use Donaldson's Diagonalization theorem as well as an unknotting obstruction due to Ozsv\'ath and Szab\'o to partially classify which pretzel knots P(2,k,-k) have unknotting number one, where k>0, odd. The Ozsv\'ath-Szab\'o obstruction is a consequence of Heegaard Floer homology. Finally in Chapter 5 we explain why the techniques used in this paper cannot be used on the remaining cases. / text

In this dissertation we prove that if an n-stranded pretzel knot K has an essential Conway sphere, then there exists an Alexander grading s such that the rank of knot Floer homology in this grading, [mathematical equation], is at least two. As a consequence, we are able to easily classify pretzel knots admitting L-space surgeries. We conjecture that this phenomenon occurs more generally for any knot in S³ with an essential Conway sphere. We also exhibit an infinite family of knots, each of which admits a nontrivial genus two mutant which shares the same total dimension of knot Floer homology, while being distinguished by knot Floer homology as a bigraded invariant. Additionally, the genus two mutation interchanges the [mathematical symbol]-graded knot Floer homology groups in [mathematical symbol]-gradings k and -k. This infinite family of examples supports a second conjecture, namely that the total rank of knot Floer homology is invariant under genus two mutation. / text

Knot theory and 3-manifold topology are closely intertwined, and few invariants stand so firmly in the intersection of these two subjects as the tunnel number of a knot, denoted t(K). We describe two very general constructions that result in knot and link pairs which are subbaditive with respect to tunnel number under connect sum. Our constructions encompass all previously known examples and introduce many new ones. As an application we describe a class of knots K in the 3-sphere such that, for every manifold M obtained from an integral Dehn filling of E(K), g(E(K))>g(M).

Thesis advisor: Tao Li / This dissertation explores a relationship between fibered knots and Heegaard splittings in closed, connected, orientable three-manifolds. We show that a fibered knot, which has a sufficiently complicated monodromy, induces a minimal genus Heegaard splitting that is unique up to isotopy. Moreover, we show that fibered knots in the three-sphere has complexity at most 3. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Mathematics.

Cette thèse porte sur deux aspects de la théorie de Morse: théorie de Morse discrète de Forman (cas de la dimension finie) et homologie de Heegaard-Floer (cas de la dimension infinie).<br />Dans une première partie, on s'intéresse au problème de relèvement de signe pour l'homologie de Heegaard-Floer combinatoire. On montre que la construction originale faite par Manolescu, Ozsváth, Szabó et D. Thurston peut être refaite de manière plus conceptuelle. On donne ensuite le lien entre ces deux constructions puis finalement on décrit un algorithme qui permet de calculer les signes.<br />La seconde partie porte sur la théorie de Morse discrète définie par Forman. Après avoir fait le lien entre l'algèbre sur les complexes de chaînes et la théorie de Morse discrète, on montre que le complexe de Thom-Smale donné par une fonction de Morse lisse sur variété lisse close peut être réalisé par une triangulation et une fonction de Morse discrète sur celle-ci. On utilise cela pour obtenir une représentation particulière sous forme de couplage complet de toute structure d'Euler sur une variété de dimension 3 close orientée.

Nous étudions un problème de chirurgie de Dehn, à savoir la caractérisation des nœuds dans les espaces lenticulaires qui admettent des chirurgies intégrales homéomorphes à S1 x S2. Nous montrons que ces nœuds sont fibrés et qu'ils bordent des surfaces de Seifert planaires. De façon équivalente, les nœuds induits dans S1 x S2 sont isotopes à des tresses. Le principal outil que nous avons utilisé est l'homologie de Heegaard-Floer, un ensemble d'invariants de type théorie de jauge développés par Ozsváth-Szabó à partir de 2000. En outre, nous montrons que ces nœuds sont simples au sens de Floer, donc conjecturalement simples. Compte tenu de cette dernière conjecture, nous avons initié une étude de nœuds simples dans les espaces lenticulaires appropriés et nous avons donné une liste potentiellement complète de tous les nœuds simples avec des chirurgies intégrales S1 x S2. Ces nœuds se révèlent être les nœuds induits dans les espaces lenticulaires obtenues en effectuant une chirurgie de Dehn sur certains nœuds doublement primitifs dans S1 x S2, exactement ceux construits par Baker. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : chirurgie de Dehn, espace lenticulaire, homologie de Heegaard-Floer, nœud fibré.

The purpose of this thesis is to define a “local” version of Ozsváth and Szabó’s Heegaard Floer homology HFL^ for links in the 3-sphere, i.e. a Heegaard Floer homology HFT^ for tangles in the 3-ball. The decategorification of HFL^ is the classical Alexander polynomial for links; likewise, the decategorification of HFT^ gives a local version ∇ˢ of the Alexander polynomial. In the first chapter of this thesis, we give a purely combinatorial definition of this polynomial invariant ∇ˢ via Kauffman states and Alexander codes and investigate some of its properties. As an application, we show that the multivariate Alexander polynomial is mutation invariant. In the second chapter, we define HFT^ in two slightly different, but equivalent ways: One is via Juhász’s sutured Floer homology, the other by imitating the construction of HFL^. We then state a glueing theorem in terms of Zarev’s bordered sutured Floer homology, which endows HFT^ with additional structure. As an application, we show that any two links related by mutation about a (2,−3)-pretzel tangle have the same δ-graded link Floer homology. This result relies on a computer calculation. In the third and last chapter, we specialise to 4-ended tangles. In this case, we give a reformulation of HFT^ with a glueing structure in terms of (what we call) peculiar modules. Together with a glueing theorem, we can easily recover oriented and unoriented skein relations for HFL^. Our peculiar modules also enjoy some symmetry relations, which support a conjecture about δ-graded mutation invariance of HFL^. However, stronger symmetries would be needed to actually prove this conjecture. Finally, we explore the relationship between peculiar modules and twisted complexes in the wrapped Fukaya category of the 4-punctured sphere. There are four appendices, some of which might be of independent interest: In the first appendix, we describe a general construction of dg categories which unifies all algebraic structures used in this thesis, in particular type A and type D modules from bordered theory. In the second appendix, we prove a generalised version of Kauffman’s clock theorem, which plays a major role for our decategorified invariants. The last two appendices are manuals for two Mathematica programs. The first is a tool for computing the generators of HFT^ and the decategorified tangle invariant ∇ˢ. The second allows us to compute bordered sutured Floer homology using nice diagrams.