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Intermediate and Power-Law Inflation in the Tachyon Model with Constant Sound Speed

By adopting the intermediate and power-law scale factors, we study the tachyon inflation with constant sound speed. We perform some numerical analysis on the perturbation and non-gaussianity parameters in this model and compare the results with observational data. By using the constraints on the scalar spectral index and tensor-to-scalar-ratio, obtained from Planck2018 TT, TE, EE+lowE+lensing+BAO+BK14 data, the constraint on the running of the scalar spectral index obtained from Planck2018 TT, TE, EE+lowEB+lensing data, and constraint on tensor spectral index obtained from Planck2018 TT, TE, EE +lowE+lensing+BK14+BAO+LIGO and Virgo2016 data, we find the observationally viable ranges of the model's parameters at both $68\%$ CL and $95\%$ CL. We also analyze the non-gaussian features of the model in the equilateral and orthogonal configurations. Based on Planck2018 TTT, EEE, TTE and EET data, we find the constraints on the sound speed as $0.276\leq c_{s}\leq 1$ at $68\%$ CL, $0.213\leq c_{s}\leq 1$ at $95\%$ CL, and $0.186\leq c_{s}\leq 1$ at $97\%$ CL.