Viable mimetic completion of unified inflation-dark energy evolution in modified gravity

In this paper, we demonstrate that a unified description of early and late-time acceleration is possible in the context of mimetic F(R) gravity. We study the inflationary era in detail and demonstrate that it can be realized even in mimetic F(R) gravity where traditional F(R) gravity fails to describe the inflation. By using standard methods we calculated the spectral index of primordial curvature perturbations and the scalar-to-tensor ratio. We use two F(R) gravity models and as it turns out, for both the models under study the observational indices are compatible with both the latest Planck and the BICEP2/Keck array data. However, this is only true under some model-dependent fine-tuning, which constrains the models we study. Finally, the graceful exit from inflation issue is addressed, and as we show, the curvature perturbations may trigger the graceful exit from inflation when the slow-roll era ends. However, fine-tuning is needed in order to produce enough inflation by the end of the slow-roll era.