Phenomenology of a realistic accelerating universe using tracker fields

We present a realistic scenario of tracking of scalar fields with varying equation of state. The astrophysical constraints on the evolution of scalar fields in the physical universe are discussed. The nucleosynthesis and the galaxy formation constraints have been used to put limits on Ω_φ and estimate ɛ during cosmic evolution. Interpolation techniques have been applied to estimate ɛ ⋍0.772 at the present epoch. The epoch of transition from matter to quintessence dominated era and consequent onset of acceleration in cosmic expansion is calculated and taking the lower limit Θ _n ^/0 =0.2 as estimated from SN _e I _a data, it is shown that the supernova observations beyond redshift z=1 would reveal deceleration in cosmic expansion.