# Physics and Astronomy Seminars

**Zoom Meeting ID**: 528-837-086**Password**: (send email to Karie.Hyslop@umontana.edu for password information)

### 2:00 PM “Topology and Mathematical Physics”

Kit Fieldhouse, U of MT Physics Major

Relatively recent work by Atiya, Segal, and Witten have shown the intimate link between modern formulations of quantum field theory and mathematical topology. Mainly, this was through Atiya and Segal's formalization of a set of axioms which one can use to define a field theory whose action does not reference the metric of spacetime. Due to this, a field theory developed (called a Topological Quantum Field Theory or TQFT) which is able to calculate topological invariants of an underlying manifold. This is interesting to physicists since it is hypothesized that a theory of quantum gravity will be independent of the topology of spacetime. In addition, TQFTs have mathematical importance as well; Witten showed that TQFTs are able to give a path integral representation of the Jone's polynomials in Knot theory. In this talk I will give a brief introduction to the principles of topology and Knot theory as well as the principles behind TQFTs. Once these foundations have been established, I will outline the argument of how these theories are able to join physics and the abstract formulations of topology.

### 3:00 PM “Rubidium Spectroscopy”

Jay Evans, U of MT Physics Major

Rubidium is one of several heavier-than-iron elements (also known as neutron (n) - capture elements) that have recently been detected in planetary nebulae. The abundance of such elements can provide unique insight into stellar nucleosynthesis and the chemical development of our galaxy. However, accurate determinations of Rubidium’s abundance depend on the availability of accurate atomic data such as absolute photoionization cross sections, but these data are largely unknown for the majority of n-capture element ions including Rb. Using a merged-beams apparatus at the Advanced Light Source at Lawrence Berkeley National Laboratory, absolute single photoionization cross-section measurements of Rb5+ ions were performed at photon energies spanning the ground state and several metastable state ionization thresholds. These data were then analyzed and compared to theoretical results and published NIST values. In this talk the motivations, techniques, and results of the experiment will be described and compared to earlier efforts by this research group.