## Departmental PhD Thesis Exam – Andrew Colinet

Wednesday, August 18, 2021
11:00 a.m. (sharp)

PhD Candidate: Andrew Colinet
Supervisor: Robert Jerrard
Thesis title: Geometric Behaviour of Solutions to Equations of Ginzburg-Landau
Type on Riemannian Manifolds

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In this thesis, we demonstrate the existence of complex-valued solutions to the Ginzburg-Landau equation
$-\Delta{}u+\frac{1}{\varepsilon^{2}}u(|u|^{2}-1)=0\hspace{20pt}\text{on }M,$

for $\varepsilon\ll1$, where $M$ is a three dimensional compact manifold without boundary, that have interesting geometric properties. Specifically, we argue the existence of solutions whose vorticity concentrates about an arbitrary closed nondegenerate geodesic on $M$.
In doing this, we extend the work of \cite{JSt} and \cite{Mes} who showed that there are solutions whose energy converges, after rescaling, to the arclength of a geodesic as above.

An important ingredient in the proof is a heat flow argument, which requires detailed information about limiting behaviour of solutions of the parabolic Ginzburg-Landau equation. Providing the necessary limiting behaviour is the other contribution of this thesis. In fact, more is achieved. Provided that $N\ge3$, we give a structural description of the limiting behaviour of solutions to the parabolic Ginzburg-Landau equation on an $N$-dimensional compact manifold without boundary $(M,g)$. More specifically, we are able to show that the limit of the renormalized energy measure orthogonally decomposes into a diffuse part, absolutely continuous with respect to the volume measure on $M$ induced by $g$, and a concentrated vortex part, supported on a codimension $2$ surface contained in $M$. Moreover, the diffuse part of the limiting energy has its time evolution governed by the heat equation while the concentrated part evolves in time according to a measure theoretic version of mean curvature flow. This extends the work of \cite{BOS2} who proved this for $N$-dimensional Euclidean space provided that $N\ge2$.

A copy of the thesis can be found here: Andrew_Colinet_Thesis