Quintessential power-law cosmology: Dark energy equation of state

Power-law cosmology with scale factor as power of cosmic time, a ∝t^α, is investigated. We review and discuss value of α obtained from various types of observation. Considering dark energy dominant era in late universe from z < 0.5, we use observational derived results from Cosmic Microwave Background (CMB) (WMAP7), Baryon Acoustic Oscillations (BAOs) and observational Hubble data to find power exponent α and other cosmological variables. α is found to be 0.99 ±0.02 (WMAP7+BAO+H₀) and 0.99 ±0.04 (WMAP7). These values do not exclude possibility of acceleration at 1σ hence giving viability to power-law cosmology in general. When considering scenario of canonical scalar field dark energy with power-law cosmology, we derive scalar field potential, exact scalar field solution and equation of state parameter. We found that the scenario of power-law cosmology containing dynamical canonical scalar field predicts present equation of state parameter w_{φ, 0} = -0.449±0.030 while the wCDM with WMAP7 data (model independent, w constant) allows a maximum (+1σ) value of w_{φ, 0} at -0.70 which is off the prediction range. However, in case of varying w _φ, the w_{φ, 0} value predicted from quintessential power-law cosmology is allowed within 1σ uncertainty.