Late Time Acceleration of the Universe from Quantum Gravity

Xiankai Pang

doi:10.3390/universe8030163

Abstract

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 the 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 the proper choice of the parameters, w will approach −1, leading to an accelerating phase dominated by the cosmological constant effectively.

Highlights

Since its discovery [1,2], the accelerating expansion of our universe remains a challenge to theoretical physics
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 acceleration of the universe can be reproduced within the formalism of an asymptotically safe cosmology [8], of the Dvali–Gabadadze–Porrati braneworld model [9], and of condensate cosmology in group field theory (GFT) [10], without the need for dark energy or the cosmological constant

Summary

Introduction

Since its discovery [1,2], the accelerating expansion of our universe remains a challenge to theoretical physics. The simplest candidate would be the cosmological constant Λ [4], but the smallness of its observed value [5], compared to the theoretical expectations from the vacuum energy of particle physics [6] or from the renormalisation flow of couplings in general relativity (GR) [7], make it difficult to find a compelling origin of Λ Another route, besides the more particle-theoretic approach, is to modify gravity theory [3]. The cosmological evolution can be extracted from suitably constructed condensate states, which include a large number of quanta to recover the continuum limit [15–22] In this formalism, the universe can be viewed as a quantum fluid constituted by GFT quanta, and its dynamics follows from the fundamental GFT theory through a hydrodynamic approximation.

Condensate Cosmology in GFT

Late Time Acceleration of the Universe

Discussion