The angular size–redshift relation in power-law cosmologies

Abstract

A linear evolution of the cosmological scale factor is a feature in several models designed to solve the cosmological constant problem via a coupling between scalar or tensor classical fields to the space-time curvature as well as in some alternative gravity theories. In this paper, by assuming a general time dependence of the scale factor, R ∼ t α , we investigate observational constraints on the dimensionless parameter α from measurements of the angular size for a large sample of milliarcsecond compact radio sources. In particular, we find that a strictly linear evolution, i.e., α ≃ 1 is favoured by these data, which is also in agreement with limits obtained from other independent cosmological tests. The dependence of the critical redshift zm (at which a given angular size takes its minimal value) with the index α is briefly discussed.

Flat Cosmology with Coupled Matter and Dark Energy

“…In fact, it has been argued (Vishwakarma 2003) that absorption by intergalactic dust of light traveling over immensely long distances might explain the faintness of extragalactic SNe Ia, obviating the need for a cosmic-accelerationbased explanation. Yet we are inclined to believe that our supernova results for the coasting universe scenario are more robust because of their concordance with those of Jain et al (2003), which are obtained by a different approach. A flat cosmology with dark energy of constant w de and matter density parameter m held at m ¼ 0:3 was also considered by Dicus & Repko (2004), who, however, assumed noninteracting dark energy and used the larger set of the supernova ''gold'' data.…”

“…The constant-w de 6 ¼ À1=2 and the third models have the same z m ¼ 1:65, whereas the coasting universe and model 2 have z m ¼ 1:72 (the same as that of Jain et al 2003) and 1.71, respectively. Thus, the minimal redshift cannot, by itself, effectively discriminate between these models.…”

Determining the equation of state of dark energy from angular size of compact radio sources and X-ray gas mass fraction of galaxy clusters

“…As pointed out by the authors of previous analyses on databases of angular size-redshift (Jackson & Dodgson 1997;Gurvits et al 1999;Vishwakarma 2001;Alcaniz 2002;Zhu & Fujimoto 2002;Jain et al 2003;Chen & Ratra 2003;Jackson 2003), when one uses the angular size data to constrain the cosmological parameters, the results will be strongly dependent on the characteristic length l. Therefore, instead of assuming a specific value for l, we have worked on the interval Figure 2 displays the 68.3% and 95.4% confidence level contours in the (Ω m , ω x ) plane using the lower shaded and the lower plus darker shaded areas respectively. It is clear from the figure that ω x is poorly constrained from the angular size-redshift data alone, which only gives ω x < −0.32 at a 95.4% confidence level.…”

Higher Dimensional Cosmological Model of the Universe with Decaying Λ Cosmology with Varying G

“…Jain et al [15] and Dev et al [16] have discussed the solutions of the form R ∝ t N in the four dimensional space-time. In our case we get R ∝ t and t = 1 H which gives the best estimation for age of the universe.…”