We investigate whether interaction between massive neutrinos and quintessence scalar field is the origin of the late time accelerated expansion of the universe. We present explicit formulas of the cosmological linear perturbation theory in the neutrinos probes of dark-energy model, and calculate cosmic microwave background anisotropies and matter power spectra. In these models, the evolution of the mass of neutrinos is determined by the quintessence scalar field, which is responsible for a varying effective equation of states; ω ef f (z) goes down lesser than -1. We consider several types of scalar field potential and put constraints on the coupling parameter between neutrinos and dark energy. By combining data from cosmic microwave background (CMB) experiments including the WMAP 3-year results, large scale structure with 2dFGRS data sets, we constrain the hypothesis of massive neutrinos in the mass-varying neutrino scenario. Assuming the flatness of the universe, the constraint we can derive from the current observation is m ν < 0.45 eV at 1σ (0.87 eV at 2σ) confidence level for the sum over three species of neutrinos. The dynamics of scalar field and the impact of scalar field perturbations on cosmic microwave background anisotropies are discussed. We also discuss on the instability issue and confirm that neutrinos are stable against the density fluctuation in our model.
IntroductionAfter Type Ia Super Novae (SNIa) [1] and Cosmic Microwave Background [2] observations in the last decade, the discovery of an accelerating expansion of the universe is a major challenge to particle physics and cosmology. Many models to explain such an accelerating expansion have been proposed so far, and they are mainly categorized into three: namely, a non-zero cosmological constant [3], a dynamical cosmological constant (quintessence scalar field) [4,45], modifications of Einstein Theory of Gravity [5]. One often call what drives the late-time cosmic acceleration as dark energy.While the existence of such dark energy component has become observationally evident, the current observational data sets are consistent with all of the three possibilities above. The first observational goal to be achieved is therefore to know whether the dark energy is cosmological constant or dynamical component; in other words, the equation of state parameter of dark energy, w = P/ρ, is −1 or not. The scalar field model like quintessence is a simple model with time dependent w, which is generally larger than −1. Because the different w leads to a different expansion history of the universe, the geometrical measurements of cosmic expansion through observations of SNIa, CMB, and Baryon Acoustic Oscillations (BAO) can give us tight constraints on w. Recent compilations of those data sets suggest that the dark energy is consistent with cosmological constant [6,7].Further, if the dark energy is dynamical component like a scalar field, it should carry its density fluctuations. Thus, the probes of density fluctuations near the present epoch, such as cross corr...
