1210.5550 (Rachan Rangdee et al.)

Tachyonic (phantom) power-law cosmology    [PDF]

Rachan Rangdee, Burin Gumjudpai

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 ($z < 2$ for power-law and $z<0.45$ for phantom power-law). WMAP7 and its combined data are used to constraint the model. For quintessence and tachyonic field, forms of the equation of state do not depends on type of the scalar field but depend only on scale factor function. However the forms of potential and the field solution are different in quintessence and tachyonic cases. Power-law cosmology model (driven with either quintessence or tachyonic field) predicts equation of state unmatched to the observational value, hence the model is excluded for quintessence and tachyonic field. The phantom power-law cosmology model predicts values of equation of state which agree with observational data (true 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 $\b$ must be less than -6, so that the $-2 < w_{\phi, 0} < -1$. The phantom power-law tachyonic potential is reconstructed. The dimensionless potential slope variable $\Gamma$ at present is about 1.5. The potential reduced to $V= V_0\phi^{-2}$ in the limit $\Omega_{\m, 0} \rightarrow 0$.

View original: http://arxiv.org/abs/1210.5550