Big bounce, slow-roll inflation, and dark energy from conformal gravity

Abstract

We examine the cosmological sector of a gauge theory of gravity based on the SO(4,2) conformal group of Minkowski space. We allow for conventional matter coupled to the spacetime metric as well as matter coupled to the field that gauges special conformal transformations. An effective vacuum energy appears as an integration constant, and this allows us to recover the late time acceleration of the universe. Furthermore, gravitational fields sourced by ordinary cosmological matter (i.e. dust and radiation) are significantly weakened in the very early universe, which has the effect of replacing the big bang with a big bounce. Finally, we find that this bounce is followed by a period of nearlyexponential slow roll inflation that can last long enough to explain the large scale homogeneity of the cosmic microwave background. * geg@unb.ca †

Bouncing Cosmology for Entropy Corrected Models in Horava-Lifshitz Gravity and Fractal Universe

“…After discussing briefly about the Hořava-Lifshitz gravity, we have formulated the modified field equations in logarithmic and Figs. [14][15][16] show the dynamical behaviors of the scale factor a, the sum of the energy density and pressure (ρ + p) and the energy density ρ during the bounce period for power law corrected model in fractal universe. power law versions of entropy corrected models in Hořava-Lifshitz gravity.…”

“…The evolution of the scale factor a, the sum of the energy density and pressure (ρ + p) and the energy density ρ during the bounce period for power law corrected model in fractal universe are shown in Figs. [14][15][16]. A barotropic equation of state p = γρ is assumed for the matter content.…”

“…Another alternative to standard big bang cosmology (to avoid the big bang singularity) is oscillating universe where the big bang is replaced by cyclical evolution [10]. In the literatures, several authors have been studied the bouncing cosmology [11,12,13,14,15]. The bouncing cosmology has been studied in modified gravity theories eg.…”

Bouncing universe in the contexts of generalized cosmic Chaplygin gas and variable modified Chaplygin gas

“…A bouncing universe has an initial narrow state by a minimal radius and then develops to an expanding phase [15], which means that the universe was arriving to the Big Bang era after the bouncing and so the equation of state parameter should cross from ω < −1 to ω > −1. Several studies in bouncing cosmology could be found in literatures [16][17][18][19][20][21][22]. On the other hand, the bouncing cosmology has also been studied in the framework of some modified theories of gravity eg.…”

Schwarzschild and linear potentials in Mannheim’s model of conformal gravity

“…Several papers, (Edery & Paranjape 1998;Walker 1994;Yoon 2013), have shown that a linear potential of Mannheim type is incompatible with observations; in the present paper we show that a linear potential is not a consequence of the the field equations of conformal gravity, so these critiques are not needed. Gegenberg et al (2017) have used fourth-order gravity to try to understand inflation in the early Universe and accelerated expansion at late times (see also Gegenberg et al 2016;Gegenberg & Seahra 2018). This work deals with the Universe in the large, and is not directly connected with the present paper, which considers objects of the scale of galaxies or the Solar System.…”