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arXiv · 2208.01413

Unifying turnaround-bounce cosmology in a cyclic universe considering a running vacuum model

A. Khodam-Mohammadi
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Abstract

Among many models which can describe the bouncing cosmology, A matter bounce scenario that is deformed by a running vacuum model of dark energy (RVM-DE) has been interested. In this research, I show that a class of RVM-CDM (cold dark matter) model can also describe a cyclical cosmology in which the universe undergoes cycles of expansion to the contraction phase and vice versa. To this end, following our previous work, I consider one of the most successful class of RVM-CDM model in bouncing cosmology, $\rho_x=n_0+n_2 H^2 +n_4 H^4$, in which the power spectral index gets a red tilt and the running of the spectral index may give a negative value by choosing the appropriate value of parameters ($n_0,~n_2,~n_4$), which is consistent with the cosmological observations. It is worthwhile to mention that most matter bounce models do not produce this negative value. However, the main purpose of this article is to investigate the RVM-CDM model in the turnaround phase. Far from the bounce in a phantom expanding universe, the turnaround conditions are investigated before the occurrence of a sudden big rip. By analyzing the Hubble parameter, equation of state parameter, and deceleration parameter around the turnaround, we show that a successful turnaround may occur after an expansion in an \textbf{interacting} case of RVM-CDM by choosing the appropriate value of parameters. A minimum value for the interaction parameter is obtained and also finds any relation between other model parameters. Finally, the effect of each parameter on a turnaround is studied, and we see that the transition time from accelerating to decelerating expansion can occur earlier for larger values of interaction parameters. Also, in several graphs, the effect of the second term in DE density, including $H^2$, is studied, and we see that by increasing its coefficient, $n_2$, the transition point leads to lower values.

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A. Khodam-Mohammadi. 2022-07-31. Unifying turnaround-bounce cosmology in a cyclic universe considering a running vacuum model. https://doi.org/10.1142/s0217732322501279

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