The evidence of cosmic acceleration and observational constraints

Abstract

Directly comparing the 6 expansion rates measured by type Ia supernovae data and the lower bound on the expansion rate set by the strong energy conditions or the null hypothesis that there never exists cosmic acceleration, we see 3σ direct evidence of cosmic acceleration and the Rh = ct model is strongly excluded by the type Ia supernovae data. We also use Gaussian process method to reconstruct the expansion rate and the deceleration parameter from the 31 cosmic chronometers data and the 6 data points on the expansion rate measured from type Ia supernoave data, the direct evidence of cosmic acceleration is more than 3σ and we find that the transition redshift z t = 0.60 +0.21 −0.12 at which the expansion of the Universe underwent the transition from acceleration to deceleration. The Hubble constant inferred from the cosmic chronometers data with the Gaussian process method is H 0 = 67.46 ± 4.75 Km/s/Mpc. By fitting two different two-parameter models to the observational data, we find that the constraints on the model parameters from either the full distance modulus data by the Pantheon compilation or the compressed expansion rate data are very similar, and the derived Hubble constants are consistent with the Planck 2018 result. Our results confirm that the 6 compressed expansion rate data can replace the full 1048 distance modulus data from the Pantheon compilation. We derive the transition redshift z t = 0.61 +0.24 −0.16 by fitting a simple q(z) model to the combination of cosmic chronometers data and the Pantheon compilation, the result is consistent with that obtained from the reconstruction with Gaussian process.

Modeling of accelerating Universe with bulk viscous fluid in Bianchi V space-time

“…In our derived model, the Universe undergoes a smooth transition from a decelerated phase of expansion to an accelerated phase at a transition redshift z t = 0.73. The extracted value of the transition redshift is compatible to some recent constraints [69][70][71][72][73]. The transitioning Universe, we have obtained in the present work has a deceleration parameter q 0 = −0.59 at the present epoch.…”

“…The transition from a decelerated phase to an accelerated phase occurs at the transition redshift z t = 0.73. This transition redshift value is compatible to the recently constrained value z t = 0.74 ± 0.05 of Farooq and Ratra [69], z t = 0.82 ± 0.08 of Busca [70], z t = 0.69 +0.23 −0.12 of Lu et al [71], z t = 0.60 +0.21 −0.12 of Yang and Gong [72] and z t = 0.7679 +0.1831 −0.1829 of Capozziello et al [73]. In a recent analysis, the deceleration parameter at the present epoch is obtained to be q 0 = −1.08 ± 0.29 [74].…”

Accelerating Universe with binary mixture of bulk viscous fluid and dark energy

“…This value of transition redshift is compatible with its values obtained in Refs. [91][92][93][94][95]. It is worthwhile to note that in recent times, there has been significant researches which gives clue that a non -ΛCDM model may solve H 0 tension problem [107][108][109][110][111][112][113][114][115][116].…”

“…It is worthwhile to note that in Capozziello et al [90], the authors have obtained q 0 = −0.56 ± 0.04 which is quite closer to the value of q 0 , constrained in this paper. Recently, the values of transition redshift are constrained as z t = 0.74 ± 0.05 [91], z t = 0.82 ± 0.08 [92], z t = 0.69 +0.23 −0.12 [93], z t = 0.60 +0.21 −0.12 [94], z t = 0.7679 +0.1831 −0.1829 [95] and z t = 0.72 ± 0.04 [96].…”

Structure formation in mimetic gravity

“…Observations confirm that almost 26% of the energy budget of the universe correspond to the DM sector, while around 69% constitute the DE [71]. There are enough evidences that support the existence of DM and DE in the universe [72].…”