Doctoral defence: Kristjan Müürsepp "Phenomenological implications of Standard Model extensions“

On 27 September at 14:15 Kristjan Müürsepp will defend his doctoral thesis „Phenomenological implications of Standard Model extensions“  for obtaining the degree of Doctor of Philosophy (in Physics).

Supervisors:
Dr. Luca Marzola, National Institute of Chemical Physics and Biophysics
Dr. Martti Raidal, National Institute of Chemical Physics and Biophysics

Oponent:
Prof. Kimmo Kainulainen, Jyväskylä University (Finland)

Summary

The Standard Model is currently the most apt description for the properties and interactions of the observed elementary particles. Nevertheless, it involves unsolved problems that point towards the possibility of beyond the SM physics. In this Thesis, we investigate possible extensions of the SM that allow to study the implications of beyond the SM physics in more detail.
By adding dark quarks and photon on top of the SM ones, one can explain the several order of magnitude difference in quark masses, vacuum stability and explain the decays of mesons that are composite particles made of quarks. In this way we acquire a more comprehensive understanding of the properties of quarks and the associated composite particles, and also are able to make predictions for future experiments. The study of vacuum stability is important, because the Higgs vacuum determines the properties of all the elementary particles that we know of, and so if this vacuum was unstable, the properties of our Universe would be drastically different. Moreover, the new dark quarks can also provide a valid dark matter candidate.
Secondly, we studied consistent theories of spin-3/2. All elementary particles have an internal angular momentum that we call the spin of the particle. While for the SM particles, the highest spin is equal to 1, it is possible that extensions of the SM also include higher spin particles, for instance to explain dark matter. Higher spin theories are complicated, which is why inconsistent theories may lead to violation of causality. In this Thesis, we study a theory which allows to overcome this issue due to a different mathematical approach. This theory was then applied to compute the indirect effects of spin-3/2 particles to the anomalous magnetic moment of muon. Muon is the heavier cousin of electron and its magnetic moment describes its interaction with a magnetic field due to quantum corrections. Even though our theory did not allow to explain the difference between the experimentally observed magnetic moment from the SM prediction, it was not ruled out by experiment either, while the calculation itself allowed us to present a practical example of computing quantum corrections with higher spin fields consistently.