| 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. |
