Search

The axion is a hypothetical elementary particle postulated by the Peccei-Quinn theory to resolve the strong CP problem in QCD. If axions exist and have low mass, they are a candidate for dark matter as well. So far our knowledge of the properties of the QCD axion rests on semi-classical arguments and effective theory. In this Letter we perform a fully dynamical investigation of the Peccei-Quinn theory, focussing on the impact of QCD on key axion parameters, by simulating the Peccei-Quinn-Weinberg-Wilczek action on the lattice. The results of the simulation, including the axion mass and effective potential, are found to be in contradiction with current axion phenomenology and question the validity and use of the Peccei-Quinn theory.

The axion is a hypothetical elementary particle postulated by the Peccei-Quinn theory to resolve the strong CP problem in QCD. If axions exist and have low mass, they are a candidate for dark matter as well. So far our knowledge of the properties of the QCD axion rests on semi-classical arguments and effective theory. In this work we perform, for the first time, a fully dynamical investigation of the Peccei-Quinn theory, focussing on the axion mass, by simulating the theory on the lattice. The results of the simulation are found to be in conflict with present axion phenomenology., Comment: 16 pages, 9 figures; theoretical considerations refined, numerical results on larger lattices added, text corrected and improved

The lack of experimental evidence for CP violation in the strong nuclear force led to the development of Peccei-Quinn theory which proposes a mechanism by which CP violation is suppressed in the strong force. One consequence of Peccei-Quinn theory is the prediction of a new boson, the axion, with an unknown mass and coupling constant. Although experiments have searched for these axions, we have only been able to place limits on the mass and coupling constant. We seek to perform a search for axions using the high purity germanium detectors in the Majorana Demonstrator to look for axion-to-photon converted signals from the sun. To do this we use the germanium crystal lattice to Bragg scatter the incident solar axion ux, which by the Primakoff effect is converted into a photon signal detectable by our germanium crystals. The work described in this document serves to establish a procedure for determining the germanium crystal axes (needed to find the Bragg condition), as well as to perform research and development on the hardware and software tools necessary to perform the axion search.

This thesis deals with the study of light-by-light scattering in the Standard Model of particle physics and in its extension predicted by Peccei-Quinn theory. It compares photon induced lepton pair productions with the hypothetical axion-like particle production, which could mediate light-by-light scattering, based on Monte Carlo simulations. Furthermore, it applies non-parametric Bayesian approach, the Gaussian Process, to model smooth background based on the invariant mass of scattered diphotons observed in ultraperipheral collisions with the ATLAS experiment. The estimated background is then used with simulated signal injection representing production of axion-like particle to determine the detection probability.

This thesis details work conducted as part of the experimental collaboration responsible for the neutron electric dipole moment (nEDM) experiment based at the Paul Scherrer Institute (PSI). The nEDM is a sensitive probe of a broad range of new CP violating physics beyond the standard model, however it remains elusive: while historic experiments since 1951 have increased in sensitivity by over six orders of magnitude, a nonzero nEDM is yet to be detected. Many theories of physics beyond the standard model predict neutron EDMs of a size that would be detectable by current and next generation experiments, and it has been said that measurements of the neutron EDM have ruled out more theories than any other experiment. One explanation of the smallness of the neutron EDM, the Peccei-Quinn theory, invokes a novel particle, the axion, which is also a credible dark matter candidate. The axion is yet to be detected.\ud \ud The work covers three main areas. First, contributions to the data analysis technique used to analyse the main dataset to produce a new world-leading limit on the neutron EDM. Second, an auxiliary measurement campaign to map the magnetic field within the experiment's magnetic shields is described, and the analysis of these datasets to provide corrections for several critical systematic effects is presented. Finally, a novel analysis of the data taken at a previous-generation nEDM experiment is used to derive the first experimental limits on the coupling of axion-like dark matter particles to gluons is described. These exclusions are up to 1000 times stronger than previous results for cosmologically interesting 10-22 eV axions.