A New Cosmological Model of Quintessence and Dark Matter

Abstract

We propose a new class of quintessence models in which late times oscillations of a scalar field give rise to an effective equation of state which can be negative and hence drive the observed acceleration of the universe. Our ansatz provides a unified picture of quintessence and a new form of dark matter we call "Frustrated Cold Dark Matter" (FCDM). FCDM inhibits gravitational clustering on small scales and could provide a natural resolution to the core density problem for disc galaxy halos. Since the quintessence field rolls towards a small value, constraints on slow-roll quintessence models are safely circumvented in our model.

Figures (1)

• Figure 1: The evolution of the dimensionless density parameter for the quintessence field $\Omega_\phi$ (solid line) is shown for the potential (\ref{['eq:pot1']}) with $p = 0.2$. Matter (dashed line) and radiation densities (dotted line) are also shown. For $z \gg 1$ the quintessence field satisfies the tracker solution (\ref{['eq:ratra']}) and contributes a fixed fraction to the total density of background matter/radiation. At later times $z \hbox{$\buildrel < \over \sim$} ~ 2$ scalar field oscillations commence and the density in the quintessence component rapidly dominates the mass density of the universe leading to $\Omega_\phi \sim 0.7$ today. In this figure the parameters of the quintessence model used are: ${\tilde{V}}_0 = 8\times 10^{-9} m_{Pl}^2 Mpc^{-2}$, $\lambda = 30 m_{Pl}^{-1}$.