A model of dark energy and dark matter

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 Lambda(Z) similar to 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 similar to(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. (c) 2006 Elsevier B.V All rights reserved.