## Dr Mark Walsh

Associate Professor

Lecturer

### Biography

I am an Associate Professor in Mathematics at Maynooth University. Up until Summer 2017 I was an Associate Professor in Mathematics at Wichita State University, Kansas, USA. I completed my PhD at the University of Oregon at Eugene, under the supervision of Professor Boris Botvinnik, and spent time as a postdoctoral researcher at WWU Muenster, Germany, as well as Oregon State University in Corvallis. My interests are in Geometry, in particular the relationship between Curvature and Topology. My work so far has focused on Positive Scalar Curvature and especially understanding the topology of the space of Riemannian metrics of positive scalar curvature on a smooth manifold. More recently I have shifted my attention to analogous questions for positive Ricci curvature.

### Research Interests

The topology of a shape is that which is maintained by continuous deformation, i.e. stretching, shrinking but not tearing. A ``topological" shape may take many geometric forms. For example, while a sphere is usually thought of as round, we may alter its shape in various ways and, provided our alterations are continuous and don't tear or puncture the sphere, we still maintain the topological condition of being a sphere. A torus (surface of a bagel) is topologically distinct from a sphere as there is no continuous way of turning one shape into the other. Such a transformation requires cutting or tearing: i.e. something discontinuous.

A large part of modern geometry concerns the problem of finding a ``good" geometric structure on a topological shape, given a plethora of possibilities. The term ``good" is highly subjective. More broadly however, one may be interested in geometries with a particular property, concerning symmetry or curvature perhaps. Given a geometric constraint, say positive curvature, the problem is to find examples of topological shapes which admit such geometries and to understand what the topological obstructions are in the ones that do not. We know for example that the round geometry is just one of many positive curvature geometries on the sphere. In the standard ``bagel shaped" torus, the inner part has negative curvature. It is a famous theorem of Mathematics that no amount of continuous deformation can give the torus everywhere positive curvature. Thus, because of its topology, the torus can not admit a positive curvature geometry.

One case of this problem is in deciding which smooth manifolds (a particular type of mathematical shape) admit Riemannian metrics (geometric structures) of positive scalar curvature (psc-metrics). This question has attracted a good deal of attention over the years and a number of significant classification results have been achieved. For manifolds which admit psc-metrics there is a related problem, of which far less is known, and which motivates my work. This problem takes the form of the following question.

What is the topology of the space of psc-metrics on a given manifold?

In other words, what is the shape of the space of geometric structures which satisfy the positive scalar curvature condition. This is a highly complicated infinite dimensional space. This problem is analogous to that of trying to understand the shape of all configurations of a robot arm. The arm itself is a $3$-dimensional object, but the space of all configurations may have many more dimensions, depending on factors such as the number of hinges on the arm. One may think of a path through this space of psc-metrics as an ``animation" of the manifold over time, gradually morphing it from one shape to another, but at every stage satisfying the curvature constraint. One may ask if given two such geometries, it is possible to continuously deform one into the other while maintaining positivity of the scalar curvature at every stage. In other words, is the space of psc-metrics path-connected? More generally, what can be said about so-called higher dimensional connectedness? Finally, what about the analogous questions for other curvature notions such as the Ricci curvature?

In recent years significant strides have been made in answering these questions and it is clear that there is a growing interest in this subject. My work forms part of those efforts.

A large part of modern geometry concerns the problem of finding a ``good" geometric structure on a topological shape, given a plethora of possibilities. The term ``good" is highly subjective. More broadly however, one may be interested in geometries with a particular property, concerning symmetry or curvature perhaps. Given a geometric constraint, say positive curvature, the problem is to find examples of topological shapes which admit such geometries and to understand what the topological obstructions are in the ones that do not. We know for example that the round geometry is just one of many positive curvature geometries on the sphere. In the standard ``bagel shaped" torus, the inner part has negative curvature. It is a famous theorem of Mathematics that no amount of continuous deformation can give the torus everywhere positive curvature. Thus, because of its topology, the torus can not admit a positive curvature geometry.

One case of this problem is in deciding which smooth manifolds (a particular type of mathematical shape) admit Riemannian metrics (geometric structures) of positive scalar curvature (psc-metrics). This question has attracted a good deal of attention over the years and a number of significant classification results have been achieved. For manifolds which admit psc-metrics there is a related problem, of which far less is known, and which motivates my work. This problem takes the form of the following question.

What is the topology of the space of psc-metrics on a given manifold?

In other words, what is the shape of the space of geometric structures which satisfy the positive scalar curvature condition. This is a highly complicated infinite dimensional space. This problem is analogous to that of trying to understand the shape of all configurations of a robot arm. The arm itself is a $3$-dimensional object, but the space of all configurations may have many more dimensions, depending on factors such as the number of hinges on the arm. One may think of a path through this space of psc-metrics as an ``animation" of the manifold over time, gradually morphing it from one shape to another, but at every stage satisfying the curvature constraint. One may ask if given two such geometries, it is possible to continuously deform one into the other while maintaining positivity of the scalar curvature at every stage. In other words, is the space of psc-metrics path-connected? More generally, what can be said about so-called higher dimensional connectedness? Finally, what about the analogous questions for other curvature notions such as the Ricci curvature?

In recent years significant strides have been made in answering these questions and it is clear that there is a growing interest in this subject. My work forms part of those efforts.

### Book

### Peer Reviewed Journal

Year | Publication | |
---|---|---|

2022 |
Walsh M.; Wraith D.J. (2022) 'H-space and loop space structures for intermediate curvatures'. Communications in Contemporary Mathematics, . [DOI] | |

2022 |
Burkemper M.; Searle C.; Walsh M. (2022) 'Positive (p,n)-intermediate scalar curvature and cobordism'. Journal of Geometry and Physics, 181 . [DOI] | |

2021 |
Botvinnik B.; Walsh M.G. (2021) 'Homotopy invariance of the space of metrics with positive scalar curvature on manifolds with singularities'. Symmetry, Integrability And Geometry: Methods And Applications (Sigma), 17 . [DOI] | |

2019 |
B. Botvinnik, M. Walsh and D. Wraith (2019) 'The Observer Moduli Space of Metrics of Positive Ricci Curvature'. Geometry and Topology, 23 :3003-3040. | |

2018 |
Mark Walsh (2018) 'Aspects of Scalar Curvature and Topology, Part 2'. BULLETIN OF THE IRISH MATHEMATICAL SOCIETY, 81 . | |

2017 |
Mark Walsh (2017) 'Aspects of Scalar Curvature and Topology, Part 1'. BULLETIN OF THE IRISH MATHEMATICAL SOCIETY, 80 . | |

2014 |
Mark Walsh (2014) 'Metrics of Positive Scalar Curvature and Generalised Morse Functions, Part 2'. Transactions of the American Mathematical Society, . | |

2014 |
Mark Walsh (2014) 'H-Spaces, Loop Spaces and Positive Scalar Curvature'. Geometry and Topology, 18 (4):2189-2243. | |

2013 |
Mark Walsh (2013) 'Cobordism Invariance of the Homotopy Type of the Space of PSC-Metrics'. Proceedings of the American Mathematical Society, . | |

2010 |
B. Botvinnik, B. Hanke, T. Schick and M. Walsh (2010) 'Homotopy Groups of the Moduli Space of Metrics of Positive Scalar Curvature'. Geometry and Topology, :2047-2076. |

### Conference Contribution

Certain data included herein are derived from the © Web of Science (2023) of Clarivate. All rights reserved.

### Committees

### Employment

### Outreach Activities

### Teaching Interests

**- Maynooth University Courses Taught (2017-present):**

MT113S: Linear Algebra 1

MT201A: Multivariable Differential Calculus

MT202A: Multivariable Integral Calculus

MT212A: Linear Algebra 2 for Mathematical Studies

MT216C: Linear Algebra 2

MT333P: Complex Analysis 1

MT342P: Groups 1

MT412C: Graph Theory

MT451P: Differential Geometry

MT212A: Linear Algebra

MT216C: Linear Algebra

MT595R: Reading Courses (Riemannian Geometry, Differential Topology, Algebraic Topology)

**- Wichita State University Courses Taught (2012-2017):**

Math 242/3: Calculus

Math 344: Vector Calculus

Math 415: Introduction to Advanced Mathematics Math 513: Abstract Algebra

Math 525: Introduction to Topology

Math 555: Differential Equations

Math 547: Advanced Calculus I

Math 640: Advanced Calculus II

Math 720: Modern Geometry

Math 725: Topology I (Graduate)

Math 825: Topology II (Graduate)

Graduate Student Seminars on Riemannian Geometry, Differential

Topology, Bordism and K-Theory, Spin Geometry

**- Oregon State University Courses Taught (2010-2012):**

Math 679: Differential Topology

Math 534/535: Differential Geometry

Math 341/342: Linear Algebra I, II

Math 255: Vector Calculus II

Math 232: Discrete Mathematics II

Math 355: Discrete Mathematics Through Guided Discovery

Math 333: Knots and Surfaces (Writing Intensive Class)

**- University of Muenster (2009-2010):**Assisted with, lectured in

Graduate Student Seminar on Atiyah-Singer Index Theorem

Graduate Student Workshop on Infinite Dimensional Lie Groups

**- University of Oregon Courses Taught (2002-2009):**

Math 256: Ordinary Differential Equations

Math 241/242, 251/252: Differential and Integral Calculus

Math 107/111/112: Calculus, Algebra, Trigonometry