String cosmology from fractional action with solitonic NS–NS matter and possibility of an accelerated expanding universe without dark energy

In this study, we discuss string cosmology with solitonic NS–NS matter, which arises when dilaton coupled p-brane gas dominates the universe and is subject to a fractional action motivated from viscosity dissipative effects occurring in the universe. Exact solutions are found from the stationary conditions of the fractional action. It was observed that the universe is non-singular, undergoing accelerated expansion in time and may not be dominated by dark energy because it is strongly affected by dissipations through the fractional parameter α. The numerical ranges of α were obtained using H(z) at the 1σ level for two independent cases: a vacuum energy dominated energy and a non-dominant vacuum energy universe. Our results are in agreement with astronomical observational limits and support both string cosmology and the fractional action cosmology.

Fractional action cosmology with an effective \(\wedge\) -term

<p>We continue studying the cosmological models derived from the fractional variational principle applied to the gravitational sector of the action functional. Within the frame of these models, the effective cosmological term could arise as a result of the non-zero Hubble parameter. At the same time, the continuity equation for the matter remains unchanged in its standard form. In this work, we are going to obtain some exact solutions for our model originating from the several kinematic assumptions. At that, we find the main cosmography parameters of the model and the corresponding equations of state of matter that fills the universe se. First, we proceed from an initially given law of evolution of the universe in some standard scenarios. Then, several exact solutions are obtained from the proposed earlier evolutionary laws for the effective cosmological term.</p>

Theoretical constraints on kinetic k-essence dark energy model in El-Nabulsi fractional action cosmology

In this work, we considered an effective scalar field theory described by a Lagrangian with a noncanonical kinetic term, which leads to accelerated expansion in the present Universe and is known as k-essence in the framework of the fractional action cosmology recently introduced by El-Nabulsi. We have chosen a particular ansatz for the scale factor and the scalar field, in which both are described as a power-law of the time, t. We have studied the behavior of some cosmological quantities in other models to obtain some useful information about the model considered. We observed that the equation of state parameter, w, has decreasing behavior and it never crosses the phantom divide line (i.e., w = –1). Studying the statefinder pair {r, s} and {w, w′}, we observed that the model considered is able to obtain the ΛCDM phase of the Universe.