Cosmic inflation in some viable modified models of f(R) gravity of polynomial-exponential form

In this paper, we present the cosmic inflation scenario in some viable models of the f(R) modified gravity of polynomial-exponential form. Results show that the magnitude of the parameter β in these viable models is at the order of 5.67x10–76 and the time of inflation is at the order of 4.6 x 10–35 s.

Super inflation mechanism with oscillating scalar fields in F(R,T) gravity

The purpose of this study is to explain the super inflation scenario for the early universe with scalar field which is minimally coupled with theory of [Formula: see text] gravity, where [Formula: see text] is the Ricci curvature scalar and [Formula: see text] is the trace of the energy–momentum tensor (EMT). We consider the model [Formula: see text], where the curvature is minimally coupled with matter. All the modification terms are properly compacted in [Formula: see text], by means of a unified solution. After a vacuum inflation, it is observed that the scalar field oscillations via the power-term in potential [Formula: see text] naturally produce the quintessential type of dark energy. Then, we observe that the matter is created by this type of dark energy during inflation. Also, the spectral index parameter and the tensor-to-scalar ratio are examined for this inflation mechanism.

Loop quantum cosmology-corrected Gauss–Bonnet singular cosmology

In this work we investigate which Loop Quantum Cosmology (LQC)-corrected Gauss–Bonnet [Formula: see text] gravity can realize two singular cosmological scenarios, the intermediate inflation and the singular bounce scenarios. The intermediate inflation scenario has a Type III sudden singularity at [Formula: see text], while the singular bounce has a soft Type IV singularity. By using perturbative techniques, we find the holonomy-corrected [Formula: see text] gravities that generate at leading order the aforementioned cosmologies and we also argue that the effect of the holonomy corrections is minor to the power spectrum of the primordial curvature perturbations of the classical theory.

Inflation and bounce from classical and loop quantum cosmology imperfect fluids

We investigate how various inflationary and bouncing cosmologies can be realized by imperfect fluids with a generalized equation of state, in the context of both classical and loop quantum cosmologies. With regards to the inflationary cosmologies, we study the intermediate inflation scenario, the [Formula: see text] inflation scenario and two constant-roll inflation scenarios, and with regards to the bouncing cosmologies, we study the matter bounce scenario, the singular bounce and the super bounce scenario. Within the context of the classical cosmology, we calculate the spectral index of the power spectrum of primordial curvature perturbations, the scalar-to-tensor ratio and the running of the spectral index and we compare the resulting picture with the Planck data. As we demonstrate, partial compatibility with the observational data is achieved in the imperfect fluid description, however none of the above scenarios is in full agreement with data. This result shows that although it is possible to realize various cosmological scenarios using different theoretical frameworks, it is not guaranteed that all the theoretical descriptions are viable.