arXiv subjects

Anthony Conway

Publications and source records attributed to Anthony Conway.

At least 19 recordsLinked to original sources

arXiv2026

Unknotting orientable surfaces

It is shown that every locally flatly embedded genus $g \in \{1,2\}$ surface in the $4$-sphere with knot group $\mathbb{Z}$ is unknotted. The same proof establishes that any two genus $g \in \{1,2\}$ surfaces in $D^4$ with knot group $\mathbb{Z}$ and common boundary an Alexander polynomial one knot are isotopic rel. boundary. In previous work, the author and Powell reduced such unknotting problems to a question concerning the cancellation of $(-t)$-quadratic forms over $\mathbb{Z}[t^{\pm 1}]$, which was solved in genus $g \geq 3$ using work of Bass. In genus $g=2$, we observe that the same proof goes through using further work of Bass. In genus $g=1,$ the result instead follows from a statement in commutative algebra which was proved with the assistance of AI. Combined with earlier work of Freedman on locally flat spheres with knot group $\mathbb{Z}$, this shows that a locally flatly embedded orientable surface in $S^4$ is unknotted if and only if its knot group is $\mathbb{Z}$.

math.GT↗

arXiv2026

Homeomorphisms of surfaces in $4$-manifolds

This paper establishes necessary and sufficient conditions for locally flat knotted surfaces in simply-connected $4$-manifolds to be equivalent. For surfaces with knot group $\mathbb{Z}_d$, we extend results of Lee-Wilczynski from spheres to surfaces of arbitrary genus; the surfaces are permitted to be nonorientable and have boundary. We prove that most projective planes with knot group $\mathbb{Z}_2$ and the same Euler number are determined by the equivariant intersection form of their exterior. We also prove that knots with prime power determinants bound at most one Moebius band in $D^4$ with knot group $\mathbb{Z}_2$ and a given Euler number. Cancellation results lead to new criteria for homologous discs to be equivalent rel. boundary. Finally, we determine the topological extendable mapping class group of knotted surfaces with abelian knot group.

math.GT↗

arXiv2026

Algebraic concordance of links

Algebraic concordance of knots can be understood from the perspective of Seifert matrices, Blanchfield forms, and homology surgery. We initiate a systematic study of algebraic concordance for links from each of these viewpoints. The present article is concerned with algebraic concordance from the perspective of homology surgery and Blanchfield forms, whereas a companion article by the third named author focuses on C-complexes and generalised Seifert matrices. The outcome of the present work consists of two obstructions to $\mu$-component links being concordant. The first obstruction, called the homology surgery invariant, takes values in the Witt group of hermitian forms over the field of fractions $Q$ of $\mathbb{Z}[\mathbb{Z}^\mu]$. The second obtruction, called the Blanchfield invariant, takes values in a Witt group of $Q/\mathbb{Z}[\mathbb{Z}^\mu]$-valued hermitian linking forms. For $\mu\le 2$, we describe these invariants in terms of generalised Seifert matrices.

math.GT↗

arXiv2026

Non-smoothable surfaces in the 4-sphere

We construct examples of non-smoothable surfaces in the $4$-sphere, thereby answering Question 4.32 on the K3 problem list. These surfaces are non-orientable and have knot group of order $2$, thus simultaneously answering Question 4.29(a) on the K3 problem list.

math.GT↗

arXiv2025

Involutions on S^4

This paper studies locally linear involutions on S^4. Our main theorem shows that any such involution with a 1-dimensional fixed-point set is necessarily linear, provided the fixed-point set admits an equivariant tubular neighborhood. The proof combines modified surgery theory with an equivariant version of the Schoenflies theorem, which we establish here. We also show that equivariant tubular neighborhoods of 1-dimensional fixed-point sets, when they exist, are not unique, in contrast to the nonequivariant case. Our results combine with earlier work to provide a classification of all locally linear involutions on S^4. As a further application, we obtain that strongly negative amphichiral knots with trivial Alexander polynomial are equivariantly topologically slice with respect to the linear action, strengthening a previous result of the first two authors. Finally, we also prove that when the fixed-point set is 2-dimensional, the involution is linear if and only if the fixed-point set is an unknotted 2-knot.

math.GT↗

arXiv2025

The first relative k-invariant

Motivated by work on the homotopy classification of $4$-manifolds with boundary, we define a relative $k$-invariant for pairs of spaces that are homotopy equivalent to CW pairs. We show that for such a pair $(X,Y)$ with Postnikov $2$-type $X \to P_2(X)$, the relative $k$-invariant is the obstruction to the existence of a section $B\pi_1(X)\to P_2(X)$ extending $Y \hookrightarrow X \to P_2(X)$. Given CW pairs $(X_0,Y_0)$ and $(X_1,Y_1)$, as well as a map $h \colon Y_0 \to Y_1$, we also prove that relative $k$-invariants provide a complete obstruction to constructing a map $X_0^{(3)} \cup Y_0 \to X_1$ that extends $h$ and induces given isomorphisms on $\pi_1$ and $\pi_2$.

math.GT↗

arXiv2025

4-manifolds with a given boundary

This paper studies the homotopy and homeomorphism classifications of $4$-manifolds with boundary. Given $4$-manifolds $X_0$ and $X_1$ with fundamental group $\pi$, we consider the problem of extending a homotopy equivalence $h \colon \partial X_0 \to \partial X_1$ to a homotopy equivalence $X_0 \to X_1$. We solve this problem in broad settings for a class of groups that includes free groups, finite cyclic groups, finite dihedral groups, solvable Baumslag-Solitar groups, and many $3$-manifold groups. When the fundamental group is additionally assumed to be good, we use surgery theory to list situations when a homeomorphism $h\colon\partial X_0 \to\partial X_1$ extends to a homeomorphism $X_0 \to X_1$. The outcome recovers results of Boyer in the simply-connected case and work of the first author and Powell when $\pi \cong \mathbb{Z}$ and the $\partial X_i$ have torsion Alexander module.

math.GT↗

arXiv2025

Simple spheres in simply-connected $4$-manifolds

These notes, which are based on three lectures delivered at the summer school "Topological 4-manifolds" at CRM in 2025, discuss classifications of locally flat spheres in closed, simply-connected $4$-manifolds, with a focus on the case where the complements of the spheres have abelian fundamental group.

math.GT↗

arXiv2025

Simply slicing knots

Given a simply-connected 4-manifold with boundary the 3-sphere, this paper establishes sufficient conditions for a knot in the boundary to be sliced by a locally flat disc in the 4-manifold, whose complement has finite cyclic fundamental group. In addition, necessary and sufficient conditions are described to ensure that such discs exist stably, that is after taking the connected sum of the 4-manifold with copies of $S^2 \times S^2$.

math.GT↗

arXiv2024

Physics Encoded Blocks in Residual Neural Network Architectures for Digital Twin Models

Physics Informed Machine Learning has emerged as a popular approach for modeling and simulation in digital twins, enabling the generation of accurate models of processes and behaviors in real-world systems. However, existing methods either rely on simple loss regularizations that offer limited physics integration or employ highly specialized architectures that are difficult to generalize across diverse physical systems. This paper presents a generic approach based on a novel physics-encoded residual neural network (PERNN) architecture that seamlessly combines data-driven and physics-based analytical models to overcome these limitations. Our method integrates differentiable physics blocks-implementing mathematical operators from physics-based models with feed-forward learning blocks, while intermediate residual blocks ensure stable gradient flow during training. Consequently, the model naturally adheres to the underlying physical principles even when prior physics knowledge is incomplete, thereby improving generalizability with low data requirements and reduced model complexity. We investigate our approach in two application domains. The first is a steering model for autonomous vehicles in a simulation environment, and the second is a digital twin for climate modeling using an ordinary differential equation (ODE)-based model of Net Ecosystem Exchange (NEE) to enable gap-filling in flux tower data. In both cases, our method outperforms conventional neural network approaches as well as state-of-the-art Physics Informed Machine Learning methods.

cs.LG↗

arXiv2024

Immersed surfaces with knot group $\mathbb{Z}$

This article is concerned with locally flatly immersed surfaces in simply-connected $4$-manifolds where the complement of the surface has fundamental group $\mathbb{Z}$. Once the genus and number of double points are fixed, we classify such immersed surfaces in terms of the equivariant intersection form of their exterior and a secondary invariant. Applications include criteria for deciding when an immersed $\mathbb{Z}$-surface in $S^4$ is isotopic to the standard immersed surface that is obtained from an unknotted surface by adding local double points. As another application, we enumerate $\mathbb{Z}$-disks in $D^4$ with a single double point and boundary a given knot; we prove that the number of such disks may be infinite. We also prove that a knot bounds a $\mathbb{Z}$-disk in $D^4$ with $c_+$ positive double points and $c_-$ negative double points if and only if it can be converted into an Alexander polynomial one knot via changing $c_+$ positive crossings and $c_-$ negative crossings. In $4$-manifolds other than $D^4$ and $S^4$, applications include measuring the extent to which immersed $\mathbb{Z}$-surfaces are determined by the equivariant intersection form of their exterior. Along the way, we prove that any two $\mathbb{Z}^2$-concordances between the Hopf link and an Alexander polynomial one link $L$ are homeomorphic rel. boundary.

math.GT↗

arXiv2024

$\mathbb{Z}$-disks in $\mathbb{C} P^2$

We study locally flat disks in $(\mathbb{C} P^2)^\circ:=(\mathbb{C} P^2)\setminus \mathring{B^4}$ with boundary a fixed knot $K$ and whose complement has fundamental group $\mathbb{Z}$. We show that up to topological isotopy rel. boundary, such disks necessarily arise by performing a positive crossing change on $K$ to an Alexander polynomial one knot and capping off with a $\mathbb{Z}$-disk in $D^4.$ Such a crossing change determines a loop in $S^3 \setminus K$ and we prove that the homology class of its lift to the infinite cyclic cover leads to a complete invariant of the disk. We prove that this determines a bijection between the set of rel. boundary topological isotopy classes of $\mathbb{Z}$-disks with boundary $K$ and a quotient of the set of unitary units of the ring $\mathbb{Z}[t^{\pm 1}]/(\Delta_K)$. Number-theoretic considerations allow us to deduce that a knot $K \subset S^3$ with quadratic Alexander polynomial bounds $0,1,2,4$, or infinitely many $\mathbb{Z}$-disks in $(\mathbb{C} P^2)^\circ$. This leads to the first examples of knots bounding infinitely many topologically distinct disks whose exteriors have the same fundamental group and equivariant intersection form. Finally we give several examples where these disks are realized smoothly.

math.GT↗

arXiv2023

Locally flat simple spheres in $\mathbb{C} P^2$

The fundamental group of the complement of a locally flat surface in a $4$-manifold is called the knot group of the surface. In this article we prove that two locally flat $2$-spheres in $\mathbb{C} P^2$ with knot group $\mathbb{Z}_2$ are ambiently isotopic if they are homologous. This combines with work of Tristram and Lee-Wilczy\'{n}ski, as well as the classification of $\mathbb{Z}$-surfaces, to complete a proof of the statement: a class $d \in H_2(\mathbb{C} P^2) \cong \mathbb{Z}$ is represented by a locally flat $2$-sphere with abelian knot group if and only if $|d| \in \lbrace 0,1,2\rbrace$; and this sphere is unique up to ambient isotopy.

math.GT↗

arXiv2023

A criterion for double sliceness

We describe a condition involving noncommutative Alexander modules which ensures that a knot with Alexander module $\mathbb{Z}[t^{\pm 1}]/(t-2) \oplus \mathbb{Z}[t^{\pm 1}]/(t^{-1}- 2)$ is topologically doubly slice. As an application, we show that a satellite knot $R_\eta(K)$ is doubly slice if the pattern $R$ has Alexander module $\mathbb{Z}[t^{\pm 1}]/(t- 2) \oplus \mathbb{Z}[t^{\pm 1}]/(t^{-1}- 2)$ and satisfies this condition, and if the infection curve $\eta \subset S^3 \setminus R$ lies in the second derived subgroup $\pi_1(S^3 \setminus R)^{(2)}.$

math.GT↗

arXiv2023

Unknotting nonorientable surfaces

Given a nonorientable, locally flatly embedded surface in the $4$-sphere of nonorientable genus $h$, Massey showed that the normal Euler number lies in $\lbrace -2h,-2h+4,\ldots,2h-4,2h \rbrace$. We prove that every such surface with knot group of order two is topologically unknotted, provided that the normal Euler number is not one of the extremal values in Massey's range. When $h$ is $1$, $2$, or $3$, we prove the same holds even with extremal normal Euler number. We also study nonorientable embedded surfaces in the 4-ball with boundary a knot $K$ in the 3-sphere, again where the surface complement has fundamental group of order two and nonorientable genus $h$. We prove that any two such surfaces with the same normal Euler number become topologically isotopic, rel. boundary, after adding a single tube to each. If the determinant of $K$ is trivial, we show that any two such surfaces are isotopic, rel. boundary, again provided that they have non-extremal normal Euler number, or that $h$ is $1$, $2$, or $3$.

math.GT↗

arXiv2022

Invariants of $2$-knots

This short survey, which was written to accompany a minicourse at the BIRS conference "Topology in dimension 4.5", concerns invariants of knotted $2$-spheres in $S^4$, also known as $2$-knots. It covers invariants extracted from the algebraic topology of the knot exterior, including Alexander invariants, the Farber-Levine pairing and Casson-Gordon invariants, as well as gauge theoretic and combinatorial invariants. Details are scarce and new results inexistant.

math.GT↗

arXiv2022

Infinite homotopy stable class for 4-manifolds with boundary

We show that for every odd prime $q$, there exists an infinite family $\{M_i\}_{i=1}^{\infty}$ of topological 4-manifolds that are all stably homeomorphic to one another, all the manifolds $M_i$ have isometric rank one equivariant intersection pairings and boundary $L(2q, 1) # (S^1 \times S^2)$, but they are pairwise not homotopy equivalent via any homotopy equivalence that restricts to a homotopy equivalence of the boundary.

math.GT↗

arXiv2022

$4$-manifolds with boundary and fundamental group $\mathbb{Z}$

We classify topological $4$-manifolds with boundary and fundamental group $\mathbb{Z}$, under some assumptions on the boundary. We apply this to classify surfaces in simply-connected $4$-manifolds with $S^3$ boundary, where the fundamental group of the surface complement is $\mathbb{Z}$. We then compare these homeomorphism classifications with the smooth setting. For manifolds, we show that every Hermitian form over $\mathbb{Z}[t^{\pm 1}]$ arises as the equivariant intersection form of a pair of exotic smooth 4-manifolds with boundary and fundamental group $\mathbb{Z}$. For surfaces we have a similar result, and in particular we show that every $2$-handlebody with $S^3$ boundary contains a pair of exotic discs.

math.GT↗