Abstract
Modifying the Einstein's gravity at large distance scales is one of the interesting proposals to explain the late time acceleration of the universe. In this Letter, we analyse scaling solutions in modified gravity models where the universe is sourced by a background matter fluid together with a tachyon type scalar field. We describe a general prescription to calculate the scaling potential in such models. Later on we consider specific examples of modifications and apply our method to calculate the scaling potential and the scale factor. Our method can be applied to any modified gravity model, in presence of tachyon field.
Highlights
Accelerated expansion of the universe has always been one of the most challenging subjects of investigation in cosmology. It plays an important role for solving major problems in standard cosmology like horizon and flatness problem
First directly observed by Supernova type Ia measurements by two independent groups in 1998 [3], today it has been confirmed by observations from new SupernovaType Ia measurements[4], Cosmic Microwave Background Radiations (CMBR)[5], and galaxy clustering by large scale redshift surveys[6]
This immediately ensures that our system of equations (6) with constant λ admits the same set of critical points to that of the standard cosmology when those solution are expressed in terms of {X, Y, λ}
Summary
Accelerated expansion of the universe has always been one of the most challenging subjects of investigation in cosmology. There are suggestions that the present acceleration of the universe is not due to any new unknown component in the cosmic soup, but due to the modifications of the gravitational physics at large distance scales In this regard, possible modifications in the Friedmann’s equation have been proposed. An effective scalar field theory governed by a Lagrangian density with a non-canonical kinetic energy term L = −V (φ)F (X), where X = −(1/2)∂μφ∂μφ, has attracted considerable attention in cosmology. Such model can lead to a late-time acceleration and is called “k-essence”[15].
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