Acceleron

Abstract: Mass-varying neutrino (MaVaN) models propose a source of dark energy in a new scalar field called the acceleron. Recent work has shown that nonrelativistic neutrino fields in these theories are unstable to inhomogeneous fluctuations, and form structures that no longer behave as dark energy. One might expect that in multiple-neutrino models, the lighter species could continue to act as a source for the acceleron, generating dark energy without the help of heavier species. This paper shows that by considering the evolution of the acceleron field for a large class of models, the result of any neutrino component becoming unstable is that all components become unstable within a short time on cosmological scales. An alternate model employing a second scalar field in a hybrid potential is shown to have stable MaVaN dark energy even in the presence of unstable heavier components.

Abstract: In the present paper we develop a concept of parallel ordinary (O) and mirror (M) worlds. We have shown that in the case of a broken mirror parity (MP), the evolutions of fine structure constants in the O- and M-worlds are not identical. It is assumed that E6-unification inspired by superstring theory restores the broken MP at the scale ~ 1018GeV, what unavoidably leads to the different E6-breakdowns at this scale: E6 → SO(10) × U(1)Z — in the O-world, and E′6 → SU(6)′ × SU(2)′Z — in the M-world. Considering only asymptotically free theories, we have presented the running of all the inverse gauge constants in the one-loop approximation. Then a "quintessence" scenario suggested in Refs. 56–61 is discussed for our model of accelerating universe. Such a scenario is related with an axion ("acceleron") of a new gauge group SU(2)′Z which has a coupling constant gZ extremely growing at the scale ΛZ ~ 10-3eV.

Abstract: We study the phenomenology of hybrid scenarios of neutrino dark energy, where in addition to a so-called mass-varying neutrino (MaVaN) sector a cosmological constant (from a false vacuum) is driving the accelerated expansion of the universe today. For general power law potentials we calculate the effective equation of state parameter weff(z) in terms of the neutrino mass scale. Due to the interaction of the dark energy field ('acceleron') with the neutrino sector, weff(z) is predicted to become smaller than −1 for z>0, which could be tested in future cosmological observations. For the scenarios considered, the neutrino mass scale additionally determines which fraction of the dark energy is dynamical, and which originates from the 'cosmological-constant-like' vacuum energy of the false vacuum. On the other hand, the field value of the 'acceleron' field today as well as the masses of the right-handed neutrinos, which appear in the seesaw-type mechanism for small neutrino masses, are not fixed. This, in principle, allows us to realize hybrid scenarios of neutrino dark energy with a 'high-scale' seesaw where the right-handed neutrino masses are close to the GUT scale. We also comment on how MaVaN hybrid scenarios with 'high-scale' seesaw might help to resolve stability problems of dark energy models with non-relativistic neutrinos.

Abstract: In this paper, I will present highlights of a recent model of dark energy and dark matter in which the present universe is 'trapped' in a false vacuum described by the potential of an axion-like scalar field (the acceleron) which is related to a new strong interaction gauge sector, SU(2)Z, characterized by a scale ΛZ ~ 3 × 10−3 eV This false vacuum model mimicks the ΛCDM scenario In addition, there are several additional implications such as a new mechanism for leptogenesis coming from the decay of a 'messenger' scalar field, as well as a new model of 'low-scale' inflation whose inflaton is the 'radial' partner of the acceleron