The dark energy phenomenon from backreacation effect. (arXiv:1707.00111v2 [astro-ph.CO] UPDATED)

<a href="http://arxiv.org/find/astro-ph/1/au:+Yao_Y/0/1/0/all/0/1">YanHong Yao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Meng_X/0/1/0/all/0/1">Xin-He Meng</a>

In this paper, we interpret the dark energy phenomenon as an averaged effect

caused by small scale inhomogeneities of the universe with the use of the

spatial averaged approach of Buchert. Two models are considered here, one of

which assumes that the backreaction term ${cal Q}_CD$ and the averaged

spatial Ricci scalar $average{CR}$ obey the scaling laws of the volume scale

factor $a_CD$ at adequately late times, and the other one adopts the ansatz

that the backreaction term ${cal Q}_CD$ is a constant in the recent universe.

Thanks to the effective geometry introduced by Larena et. al. in their previous

work, we confront these two backreaction models with latest type Ia supernova

and Hubble parameter observations, coming out with the results that the

constant backreaction model is slightly favoured over the other model, and

within $1sigma$ confidence interval of the parameter $n$ in the scaling

backreaction model, $mid{cal Q}_CDmid$ decreases with the increase of the

volume scale factor $a_CD$ at adequately late times. Also, the numerical

simulation results show that the constant backreaction model predicts a smaller

expansion rate and decelerated expansion rate than the other model does at

redshifts higher than about 1, and both backreaction terms begin to accelerate

the universe at a redshift around 0.6. In addition, by confronting the standard

cosmological model against the same datasets, we find that the effective

geometry tends to push the constraint toward a smaller cosmological constant

term.

In this paper, we interpret the dark energy phenomenon as an averaged effect

caused by small scale inhomogeneities of the universe with the use of the

spatial averaged approach of Buchert. Two models are considered here, one of

which assumes that the backreaction term ${cal Q}_CD$ and the averaged

spatial Ricci scalar $average{CR}$ obey the scaling laws of the volume scale

factor $a_CD$ at adequately late times, and the other one adopts the ansatz

that the backreaction term ${cal Q}_CD$ is a constant in the recent universe.

Thanks to the effective geometry introduced by Larena et. al. in their previous

work, we confront these two backreaction models with latest type Ia supernova

and Hubble parameter observations, coming out with the results that the

constant backreaction model is slightly favoured over the other model, and

within $1sigma$ confidence interval of the parameter $n$ in the scaling

backreaction model, $mid{cal Q}_CDmid$ decreases with the increase of the

volume scale factor $a_CD$ at adequately late times. Also, the numerical

simulation results show that the constant backreaction model predicts a smaller

expansion rate and decelerated expansion rate than the other model does at

redshifts higher than about 1, and both backreaction terms begin to accelerate

the universe at a redshift around 0.6. In addition, by confronting the standard

cosmological model against the same datasets, we find that the effective

geometry tends to push the constraint toward a smaller cosmological constant

term.

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