B. M. Roberts, Honours Thesis (UNSW) (2012)

The standard model has been extremely successful in its description of nature, however it is widely believed that it is a low energy manifestation of a more complete, unified theory. There are a number of proposed extensions to the standard model and tests must be made to distinguish between them. It is the aim of such tests to reveal, or to constrain, new physics beyond the standard model and differentiate between competing unification theories. Complementary to high energy tests (performed in accelerators, e.g. the Large Hadron Collider at CERN), parity violation measurements can serve as highly accurate tests the low energy sector of the standard model. Measurements of parity violation rely on theoretical calculations for their interpretation. It is the accuracy of these calculations which restrict the conclusions that can be drawn about physics beyond the standard model. In this thesis, we improve the current calculations for parity nonconservation in caesium by adding many-body corrections to two non-dominating terms. This result is used to interpret the most precise parity nonconservation measurement in caesium, providing the most accurate low energy test of the electroweak theory to date. After this, new parity violation calculations are performed in several atoms. Significantly, the accuracy for calculations in rubidium is shown to have the potential to surpass those of caesium. This is important because in caesium it is the theoretical uncertainty which limits the use of parity nonconservation as a test of new physics and unification theories. Then, calculations of previously neglected corrections to parity violation calculations arising from strong Coulomb field quantum electrodynamics are performed for several atoms: Rb, Fr, Ra+, Ba+ and Tl. These small corrections are important as the accuracy of atomic physics calculations in these atoms approaches the level already attained in caesium. Results from this work have been accepted for publication in Physical Review Letters.

- B. M. Roberts, Honours Thesis (2012)