Tachyonic (phantom) power-law cosmology

Tachyonic scalar field-driven late universe with dust matter content is considered. The cosmic expansion is modeled with power-law and phantom power-law expansion at late time, i.e. z ≈0.45. WMAP7 and its combined data are used to constraint the model. The forms of potential and the field solution are different for quintessence and tachyonic cases. Power-law cosmology model (driven by either quintessence or tachyonic field) predicts unmatched equation of state parameter to the observational value, hence the power-law model is excluded for both quintessence and tachyonic field. In the opposite, the phantom power-law model predicts agreeing valued of equation of state parameter with the observational data for both quintessence and tachyonic cases, i.e. w_φ,0 = -1.49^+11.64_-4.08 (WMAP7+BAO+H0) and w_φ,0 = -1.51^+3.89_-6.72 (WMAP7). The phantom-power law exponent β must be less than about -6, so that the -2 < w_φ,0 <-1. The phantom power-law tachyonic potential is reconstructed. We found that dimensionless potential slope variable Γ at present is about 1.5. The tachyonic potential reduced to V = V₀φ^-2 in the limit Ω_m,0→0.