Late Time Acceleration of the Universe from Quantum Gravity

We show that the accelerating expansion phase of the universe can emerge from the group field theory formalism, a candidate theory of quantum gravity. The cosmological evolution can be extracted from condensate states using mean field approximation, in a form of modified FLRW equations. By introducing an effective equation of state w, we can reveal the relevant features of the evolution, and show that with proper choice of parameters, w will approach to −1, corresponds to the behaviour of cosmological constant, results in a late time acceleration and leads to de Sitter spacetime asymptotically.

Continuous cosmic evolution with diffusive barotropic fluid: First-order thermodynamic phase transition

In the background of homogeneous and isotropic flat FLRW model, a complete cosmic scenario from nonsingular emergent scenario to the present late time acceleration through inflationary era and matter-dominated epoch has been presented in this work with cosmic matter in the form of diffusive barotropic fluid. By proper choices of the diffusion parameter and using Friedmann equations, it is possible to show the transitions: Emergent scenario[Formula: see text]Inflationary era[Formula: see text]matter-dominated phase[Formula: see text]Late time acceleration epoch. In analogy with analytic continuation, it is found that the above evolution will be continuous for suitable values of the parameters involved. Finally, possible first-order thermodynamic phase transition has been analyzed for such cosmic evolution.

Cosmological models with a hybrid scale factor

In this paper, we present some cosmological models with a hybrid scale factor (HSF) in the framework of general relativity (GR). The HSF fosters an early deceleration as well as a late-time acceleration and mimics the present Universe. The dynamical aspects of different cosmological models with HSF in the presence of different matter fields have been discussed.

Cosmic evolution in f(T) gravity theory

The paper deals with cosmology in modified [Formula: see text] gravity theory. With some phenomenological choices for the function [Formula: see text] it is possible to have cosmological solutions describing different phases of the evolution of the Universe for the homogeneous and isotropic Friedmann–Lemaître–Robertson–Walker (FLRW) model. By proper choice of the parameters involved in the function [Formula: see text] and also in the cosmological solutions it is shown that a continuous cosmic evolution starting from the emergent scenario to the present late-time acceleration is possible. Finally thermodynamical analysis of [Formula: see text] gravity is presented.

Invisible QCD as Dark Energy

We account for the late time acceleration of the Universe by extending the Quantum Chromodynamics (QCD) color to a S U ( 3 ) invisible sector (IQCD). If the Invisible Chiral symmetry is broken in the early universe, a condensate of dark pions (dpions) and dark gluons (dgluons) forms. The condensate naturally forms due to strong dynamics similar to the Nambu–Jona-Lasinio mechanism. As the Universe evolves from early times to present times the interaction energy between the dgluon and dpion condensate dominates with a negative pressure equation of state and causes late time acceleration. We conclude with a stability analysis of the coupled perturbations of the dark pions and dark gluons.

The Lambert W Function: A Newcomer in the Cosmology Class?

We propose a novel equation of state (EoS) which explains the evolutionary history of a flat Friedmann–Lemaitre–Robertson–Walker universe. The uniqueness of this EoS lies in the fact that it incorporates the Lambert W function in a special fashion. It is explicitly demonstrated that with observationally relevant values of the unknown parameters ϑ1 and ϑ2, all the evolutionary phases of the universe can be reproduced. Moreover, it also shows that the initial singularity is unavoidable and asserts that the late-time acceleration of the universe would continue forever.