کوروش نوذری

We consider the mimetic tachyon model in the Lagrange multiplier approach. We study both the linear and nonlinear perturbations and find the perturbation and non-Gaussianity parameters in this setup. By adopting two types of the scale factor as the power-law (a ¼ a0tn) and intermediate (a ¼ a0 expðbtβÞ) scale factors, we perform a numerical analysis on the model which is based on Planck2018 TT, TE, EE+lowE +lensing +BAO +BK14 and Planck2018 TTT, EEE, TTE and EET datasets. We show that the mimetic tachyon model with both the power-law and intermediate scale factors, in some ranges of its parameter space is instabilities-free and observationally viable. The power-law mimetic tachyon model with 26.3 < n < 33.0 and the intermediate mimetic tachyon model with 0.116 < β < 0.130 are consistent with observational data and free of the ghost and gradient instabilities.