A substantial fraction of the energy density of the universe may consist of quintessence in the form of a slowly rolling scalar field. Since the energy density of the scalar field generally decreases more slowly than the matter energy density, it appears that the ratio of the two densities must be set to a special, infinitesimal value in the early universe in order to have the two densities nearly coincide today. Recently, we introduced the notion of tracker fields to avoid this initial conditions problem. In the paper, we address the following questions: What is the general condition to have tracker fields? What is the relation between the matter energy density and the equation-of-state of the universe imposed by tracker solutions? And can tracker solutions help to explain why quintessence is becoming important today rather than during the early universe?
Physical Review D
- Pub Date:
- June 1999
- Particle-theory and field-theory models of the early Universe;
- large-scale structure of the Universe;
- Background radiations;