A model of dark energy and dark matter

Abstract A dynamical model for the dark energy is presented in which the “quintessence” field is the axion, a Z , of a spontaneously broken global U ( 1 ) A ( Z ) symmetry whose potential is induced by the instantons of a new gauge group SU ( 2 ) Z . The SU ( 2 ) Z coupling becomes large at a scale Λ Z ∼ 10 −3 eV starting from an initial value M at high energy which is of the order of the Standard Model (SM) couplings at the same scale M . A perspective on a possible unification of SU ( 2 ) Z with the SM will be briefly discussed. We present a scenario in which a Z is trapped in a false vacuum characterized by an energy density ∼ ( 10 −3 eV ) 4 . The lifetime of this false vacuum is estimated to be extremely large. Other estimates relevant to the “coincidence issue” include the ages of the universe when the a Z potential became effective, when the acceleration “began” and when the energy density of the false vacuum became comparable to that of (baryonic and non-baryonic) matter. Other cosmological consequences include a possible candidate for the weakly interacting (WIMP) Cold Dark Matter as well as a scenario for leptogenesis. A brief discussion on possible laboratory detections of some of the particles contained in the model will also be presented.