Viable intermediate inflation in the mimetic DBI model

Narges Rashidi,Kourosh Nozari

doi:10.1140/epjc/s10052-021-09619-2

Abstract

We study the intermediate inflation in the mimetic Dirac–Born–Infeld model. By considering the scale factor as a=a_{0}exp (bt^{beta }), we show that in some ranges of the intermediate parameters b and beta , the model is free of the ghost and gradient instabilities. We study the scalar spectral index, tensor spectral index, and the tensor-to-scalar ratio in this model and compare the results with Planck2018 TT, TE, EE + lowE + lensing + BAO + BK14 data at 68% and 95% CL. In this regard, we find some constraints on the intermediate parameters that lead to the observationally viable values of the perturbation parameters. We also seek the non-Gaussian features of the primordial perturbations in the equilateral configuration. By performing the numerical analysis on the nonlinearity parameter in this configuration, we show that the amplitude of the non-Gaussianity in the intermediate mimetic DBI model is predicted to be in the range -16.7<f^{equil}<-12.5. We show that, with 0<ble 10 and 0.345<beta <0.387, we have an instabilities-free intermediate mimetic DBI model that gives the observationally viable perturbation and non-Gaussianity parameters.

Highlights

A new approach to General Relativity has been proposed by Chamseddine and Mukhanov in 2003, called mimetic gravity
We have studied the intermediate inflation in the Mimetic DBI (MDBI) model
With the intermediate MDBI model, it is possible to have a mimetic gravity model that is free of ghost and gradient instabilities in some ranges of the intermediate parameters b and β

Summary

Introduction

A new approach to General Relativity has been proposed by Chamseddine and Mukhanov in 2003, called mimetic gravity. By considering the Lagrange multiplier approach and assuming the power-law inflation, we have studied the inflation and perturbations in this model and shown that this model in some ranges of the model’s parameter space is free of the ghost and gradient instabilities. [74], we have considered the tachyon field in the mimetic gravity setup and within the Lagrange multiplier approach We have adopted both power-law and intermediate scale factors and studied the inflation in the tachyon mimetic model. 4, by performing numerical analysis, we compare the results with Planck2018 observational data In this regard, we show that the intermediate MDBI model for some values of β and b, which lead to the instabilities-free model, gives observationally viable values of the perturbation parameters.

Mimetic DBI model

Intermediate MDBI model

Comparing with the Planck2018 observational data

Summary and conclusion