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. $z \lesssim 0.45$. 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. $w_{\phi, 0} = -1.49^{+11.64}_{-4.08}$ (WMAP7+BAO+$H_0$) and $w_{\phi, 0} = -1.51^{+3.89}_{-6.72}$ (WMAP7). The phantom-power law exponent $\beta$ must be less than about -6, so that the $-2 < w_{\phi, 0} < -1$. The phantom power-law tachyonic potential is reconstructed. We found that dimensionless potential slope variable $\Gamma$ at present is about 1.5. The tachyonic potential reduced to $V= V_0\phi^{-2}$ in the limit $\Omega_{{\rm m}, 0} \rightarrow 0$.