Exotic phenomenology of DFSZ axion models

Abstract

In this thesis we introduce exotic properties of the highly motivated axion particle which lead to a better accessibility in experimental searches. The axion is an essential ingredient of theories beyond the Standard Model of particle physics (SM) which aim to solve the strong CP problem manifesting in the absence of an electric dipole moment of the neutron (nEDM). The axion is mainly characterized by its mass and its coupling to SM particles with a special emphasis on the axion-diphoton coupling. Our focus lies on axion models which fall into the class of the Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) construction which is specified by direct axion-fermion couplings. This is in contrast to the Kim-Shifman-Vainshtein-Zakharov model which only accounts for axion couplings to gauge bosons. While the first part of this work is dedicated to new effects which arise in the axion potential with an influence on the axion mass, the second part deals with new interactions described within an effective field theory framework. These interactions comprise enhanced axion fermion couplings induced by a Dark Matter scalar field as well as axion couplings to the Higgs and Z boson which are generated through kinetic mixing effects in gauged U(1)' extensions.