Inflationary cosmology with Chaplygin gas in Palatini formalism

Abstract

We present a simple generalisation of the ΛCDM model which on the one hand reaches very good agreement with the present day experimental data and provides an internal inflationary mechanism on the other hand. It is based on Palatini modified gravity with quadratic Starobinsky term and generalized Chaplygin gas as a matter source providing, besides a current accelerated expansion, the epoch of endogenous inflation driven by type III freeze singularity. It follows from our statistical analysis that astronomical data favors negative value of the parameter coupling quadratic term into Einstein-Hilbert Lagrangian and as a consequence the bounce instead of initial Big-Bang singularity is preferred.

Do sewn up singularities falsify the Palatini cosmology?

“…We would like to mention that in [1] we have obtained, under the same assumptions, a model which reaches very good agreement with observational data. We were also able to find an upper bound on the value of the parameter γ in order to locate a singularity, which has appeared in the model, before the recombination epoch.…”

“…More exactly, the model possesses four phases of cosmic evolution while the big bang singularity is preserved: the decelerating phase dominated by matter, an intermediate ephemeral inflation phase corresponding to the type III singularity, a phase of matter domination (decelerating phase) and finally, the phase of acceleration of the current universe. The present paper extends and intensifies the analysis presented in [1]. Now on, for convenience of the reader, let us briefly recall the main properties of the formalism which is used in the paper.…”

“…Satisfactory explanations have not been set so far, which makes searching and examination of new models still desirable. Due to that fact we have proposed [1] and examined a model which modifies the standard one in two different ways. The first modification refers to the gravitational Lagrangian, which we have enriched with the so-called Starobinsky term γR 2 [2] keeping in mind that the parameter γ is small and estimated by observational data and analytical analysis.…”

“…The Palatini approach is very important in cosmology as the equations of motion are second order differential equations, to be compared to the standard metric approach in which the field equations give rise to fourth order ones (see e.g. [1] and references therein).…”

“…The action S m is a matter action which is independent of the connection but includes other scalar fields and depends on g μν . Because the Lagrangian for matter does not depend on the connection [1] in the model with a generalized barotropic matter satisfying equation of state p = p(ρ), it can be postulated similar to GR to have the following form [24]:…”