Seminar

Fateme Peimany, University of Waterloo

Definable groups in CCM

We continue to study the structure of groups definable in CCM, toward showing that every strongly minimal group is either a complex torus or a (commutative) linear algebraic group.

MC 5479

Viktor Majewski, University of Waterloo

Filling Holes in the Spin(7)-Teichmüller Space and String Cohomology

In this talk, I apply the analytic results from the first talk to study the boundary of the Spin(7) Teichmüller space.Using compactness results for Ricci-flat metrics together with known examples of Spin(7) manifolds, it is knownthat Spin(7) orbifolds with SU(N) isotropy arise as boundary points of the moduli space. Building on theresolution scheme for Spin(7) orbifolds that I discussed in 2024, and which I will briefly review, we show howthis boundary can be removed by requiring Spin(7) orbifolds to encode information about their resolutions. Inthis way, the Teichmüller space is enlarged to include orbifold limits together with their compatible resolutions,thereby filling in the boundary. Finally, we explain how this perspective is related to a Spin(7) analogue of thecrepant resolution conjecture from string cohomology, providing a geometric interpretation of the obstructioncomplex discussed in the linear gluing analysis in the first talk.

MC 5403

Fateme Peimany, University of Waterloo

Model Theory Working Seminar: Definable groups in CCM

We continue to study the structure of groups definable in CCM, toward showing that every strongly minimal group is either a complex torus or a (commutative) linear algebraic group.

MC 5479

Amanda Petcu, University of Waterloo

Some results on hypersymplectic structures

A conjecture of Simon Donaldson is that on a compact 4-manifold X^4 one can flow from a hypersymplectic structure to a hyperkahler structure while remaining in the same cohomology class. To this end the hypersymplectic flow was introduced by Fine-Yao. In this thesis the notion of a positive triple on X^4 is used to define a hypersymplectic and hyperkahler structure. Given a closed positive triple one can define either a closed G2 structure or a coclosed G2 structure on T^3 x X^4. The coclosed G2 structure is evolved under the G2 Laplacian coflow. This descends to a flow of the positive triple on X^4, which is again the Fine-Yao hypersymplectic flow. In the second part of this thesis we let X^4 = R^4 \0 with a particular cohomogeneity one action. A hypersymplectic structure invariant under this action is introduced. The Riemann and Ricci curvature tensors are computed and we verify in a particular case that this hypersymplectic structure can be transformed to a hyperkahler structure. The notion of a soliton for the hypersymplectic flow in this particular case is introduced and it is found that steady solitons give rise to hypersymplectic structures that can be transformed to hyperkahler structures. Some other soliton solutions are also discussed.

MC 5403

Amanda Maria Petcu, University of Waterloo

Some results on hypersymplectic structures

A conjecture of Simon Donaldson is that on a compact 4-manifold X^4 one can flow from a hypersymplecticstructure to a hyperkahler structure while remaining in the same cohomology class. To this end thehypersymplectic flow was introduced by Fine-Yao. In this thesis the notion of a positive triple on X^4 is used todefine a hypersymplectic and hyperkahler structure. Given a closed positive triple one can define either a closedG2 structure or a coclosed G2 structure on T^3 x X^4. The coclosed G2 structure is evolved under the G2Laplacian coflow. This descends to a flow of the positive triple on X^4, which is again the Fine-Yaohypersymplectic flow. In the second part of this thesis we let X^4 = R^4 \ {0} with a particular cohomogeneityone action. A hypersymplectic structure invariant under this action is introduced. The Riemann and Riccicurvature tensors are computed and we verify in a particular case that this hypersymplectic structure can betransformed to a hyperkahler structure. The notion of a soliton for the hypersymplectic flow in this particularcase is introduced and it is found that steady solitons give rise to hypersymplectic structures that can betransformed to hyperkahler structures. Some other soliton solutions are also discussed.

MC 5479

Rahim Moosa, University of Waterloo

Definable groups in CCM

I will continue totalk about “Strongly minimal groups in the theory of compact complex maniflds".

MC 5479

Amanda Petcu, University of Waterloo

Some results on hypersymplectic structures

A conjecture of Simon Donaldson is that on a compact 4-manifold X^4 one can flow from a hypersymplecticstructure to a hyperkahler structure while remaining in the same cohomology class. To this end thehypersymplectic flow was introduced by Fine-Yao. In this thesis the notion of a positive triple on X^4 is used todefine a hypersymplectic and hyperkahler structure. Given a closed positive triple one can define either a closedG2 structure or a coclosed G2 structure on T^3 x X^4. The coclosed G2 structure is evolved under the G2Laplacian coflow. This descends to a flow of the positive triple on X^4, which is again the Fine-Yaohypersymplectic flow. In the second part of this thesis we let X^4 = R^4 \0 with a particular cohomogeneity oneaction. A hypersymplectic structure invariant under this action is introduced. The Riemann and Ricci curvaturetensors are computed and we verify in a particular case that this hypersymplectic structure can be transformed toa hyperkahler structure. The notion of a soliton for the hypersymplectic flow in this particular case is introducedand it is found that steady solitons give rise to hypersymplectic structures that can be transformed to hyperkahlerstructures. Some other soliton solutions are also discussed.

MC 5403

William Dan, University of Waterloo

Random Left C.E. Reals and Solovay Reducibility

In the last seminar we discussed how the halting probability of a universal prefix-free machine is left c.e. andrandom, and asked if the converse would hold. We then studied Solovay reducibility and the resulting concept ofSolovay completeness, which turns out to be key in proving the converse. In this seminar, we will use thisconcept to prove the two theorems giving the converse, a theorem from Calude et al. and the Kucera-Slamantheorem. Then, we will go back to expand further on the properties of Solovay reducibility and how it connectsto relative randomness, and relate this connection back to the theorems we proved. This seminar follows sections9.1 and 9.2 from the Downey and Hirschfeldt book.

MC 5403

Elisabeth Werner, Case Western Reserve University

The $L_p$-Floating Area and Isoperimetric Inequalities on the Sphere

Euclidean convex bodies in spaces of constant positive curvature. We introduce the family of $L_p$-floatingareas for spherical convex bodies, as an analog to $L_p$-affine surface area measures from Euclidean geometry.We investigate a duality formula, monotonicity and isoperimetric inequalities for this new family of curvaturemeasures on spherical convex bodies. Based on joint works with Florian Besau.

MC 5417

Facundo Camano, University of Waterloo

Moduli Space Degeneration via Monopole Deformation

In this talk, I will discuss the theory behind the deformation of monopoles. I will then apply the theory to show monopole moduli spaces degenerate as a singularity is sent off towards infinity.

MC 5403