#### Degree

Doctor of Philosophy

#### Program

Mathematics

#### Supervisor

Masoud Khalkhali

#### Abstract

We introduce a pseudo-Riemannian calculus of modules over noncommutative al- gebras in order to investigate to what extent the differential geometry of classical Riemannian manifolds can be extended to a noncommutative setting. In this frame- work, it is possible to prove an analogue of the Levi-Civita theorem. It states that there exists at most one connection, which satisfies torsion-free condition and metric compatibility condition, on a given smooth manifold with fixed metric. More signif- icantly, the corresponding curvature operator has the same symmetry properties as the classical curvature tensors. We consider a pseudo-Riemannian calculus over the noncommutative 3-sphere and the noncommutative 4-sphere and explicitly determine the torsion-free and metric compatible connection, and we compute its scalar curva- ture. In the case of the noncommutative 4-sphere, we compute the scalar curvature of conformal perturbations of the round metric by localizing the algebra of noncommu- tative 4-sphere, which allows us to formulate and prove a Gauss-Bonnet-Chern type theorem. For the case of the noncommutative 4-torus, the Pfaffian of the curvature form for a conformal class of the flat metric is computed.

#### Recommended Citation

Wilson, Mitsuru, "Gauss-Bonnet-Chern type theorem for the noncommutative four-sphere" (2016). *Electronic Thesis and Dissertation Repository*. 3937.

https://ir.lib.uwo.ca/etd/3937