Abstract
In this paper, the effects of the quantum metric fluctuations on the background cosmological dynamics of the universe are considered. To describe the quantum effects, the metric is assumed to be given by the sum of a classical component and a fluctuating component of quantum origin . At the classical level, the Einstein gravitational field equations are equivalent to a modified gravity theory, containing a non-minimal coupling between matter and geometry. The gravitational dynamics is determined by the expectation value of the fluctuating quantum correction term, which can be expressed in terms of an arbitrary tensor Kμν. To fix the functional form of the fluctuation tensor, the Newtonian limit of the theory is considered, from which the generalized Poisson equation is derived. The compatibility of the Newtonian limit with the Solar System tests allows us to fix the form of Kμν. Using these observationally consistent forms of Kμν, the generalized Friedmann equations are obtained in the presence of quantum fluctuations of the metric for the case of a flat homogeneous and isotropic geometry. The corresponding cosmological models are analyzed using both analytical and numerical method. One finds that a large variety of cosmological models can be formulated. Depending on the numerical values of the model parameters, both accelerating and decelerating behaviors can be obtained. The obtained results are compared with the standard ΛCDM (Λ Cold Dark Matter) model.
Highlights
Published: 24 August 2021General relativity and quantum mechanics are the basic, and widely accepted, branches of theoretical physics, confirmed by a large number of experiments and observations
Using these observationally consistent forms of Kμν, the generalized Friedmann equations are obtained in the presence of quantum fluctuations of the metric for the case of a flat homogeneous and isotropic geometry
General relativity, a theory of gravity [1,2,3] is a typical example of a physical theory with a very beautiful geometric structure
Summary
General relativity and quantum mechanics are the basic, and widely accepted, branches of theoretical physics, confirmed by a large number of experiments and observations. The presence at the theoretical level of the particle creation processes in both quantum theories of gravity in curved space-times and in modified gravity theories with geometry-matter coupling suggests that a deep relationship may exist between these two, seemingly distinct physical theories Such a relationship was already obtained in [57], where it was found that in the nonperturbative approach for the quantization of the metric, as introduced in [55,56,58], as a consequence of the fluctuations of the spacetime, a specific f ( R, T ) type gravitational model naturally emerges.
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