Tachyon Mimetic Inflation as an Instabilities-Free Model
  We consider the mimetic tachyon model in the Lagrange multiplier approach. We
study both the linear and non-linear perturbations and find the perturbation
and non-gaussianity parameters in this setup. By adopting two types of the
scale factor as the power-law ($a=a_{0}\,t^{n}$) and intermediate
($a=a_{0}\exp(bt^{\beta})$) 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 data sets. 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 $0.116<\beta<0.130$ are consistent with observational data
and free of the ghost and gradient instabilities.
