AXIONS AND MAJORONS IN PARTICLE PHYSICS, ASTROPHYSICS AND COSMOLOGY

The motivation for the existence of the axion and the majoron is discussed and their implications in the domain of particle physics, astrophysics and cosmology are studied.; The axion arises as a byproduct of an elegant resolution of the strong CP problem which employs the Peccei-Quinn mechanism. The majoron provides a natural explanation of the smallness, if nonvanishing, of the neutrino masses, which in turn could solve the solar neutrino problem.; Both particles couple very weakly to the matter but their effect in astrophysics and cosmology is shown to be significant, from which bounds on their physical properties are derived.; An extension of the standard model is constructed that includes the Peccei-Quinn symmetry and the lepton number symmetry, both of which are spontaneously broken at the same invisible axion scale.