arXiv subjects

Wlodzimierz Godlowski

Publications and source records attributed to Wlodzimierz Godlowski.

41 records · Page 3Linked to original sources

arXiv2004

Brane Universes Tested by Supernovae Ia

We discuss observational constrains coming from supernovae Ia imposed on the behaviour of the Randall-Sundrum models. In the case of dust matter on the brane, the difference between the best-fit Perlmutter model with a $Λ$-term and the best-fit brane models becomes detectable for redshifts $z > 1.2$. It is interesting that brane models predict brighter galaxies for such redshifts which is in agreement with the measurement of the $z = 1.7$ supernova. We also demonstrate that the fit to supernovae data can also be obtained, if we admit the "super-negative" dark energy (phantom matter) $p= - (4/3) \varrho$ on the brane, where the dark energy in a way mimics the influence of the cosmological constant. It also appears that the dark energy enlarges the age of the universe which is demanded in cosmology. Finally, we propose to check for dark radiation and brane tension by the application of the angular diameter of galaxies minimum value test. We point out the existence of coincidence problem for the brane tension parameter.

astro-ph↗

arXiv2004

Can the Stephani model be an alternative to FRW accelerating models?

A class of Stephani cosmological models as a prototype of non-homogeneous universe is considered. The non-homogeneity can lead to accelerated evolution which is now observed from the SNIa data. Three samples of type Ia supernovae obtained by Perlmutter at al., Tonry et al. and Knop et al. are taken into account. Different statistical methods (best fits as well as maximum likelihood method) to obtain estimates of the model parameters are used. Stephani model is considered as an alternative to the concordance of Lambda-CDM model in the explanation of the present acceleration of the universe. The model explains the acceleration of the universe at the same level of accuracy as the Lambda-CDM model. From the best fit analysis it follows that the Stephani model is characterized by higher value of nonrelativistic matter density parameter than the Lambda-CDM model. It is also shown that the obtained results are consistent with location of CMB peaks.

astro-ph↗

arXiv2003

Constraints on a Cardassian model from SNIa data - revisited

We discuss some observational constraints resulting only from SNIa observations, imposed on the behavior of the original flat Cardassian model, and its extension with the curvature term included. We test the models using the Perlmutter SN Ia data as well as the new Knop and Tonry samples. We estimate the Cardassian model parameters using the best-fitting procedure and the likelihood method. In the fitting procedure we use the density variables for matter, Cardassian fluid and curvature, and include the errors in redshift measurements. For the Perlmutter sample in the non-flat Cardassian model we obtain the high or normal matter density universe ($Ω_{m,0} \ge 0.3$), while for the flat Cardassian model we have the high density universe. For sample A in the high density universe we also find the negative values of estimates of $n$ which can be interpreted as the phantom fluid effect. For the likelihood method we get that a nearly flat universe is preferred. We show that, if we assume that the matter density is 0.3, then $n \approx 0$ in the flat Cardassian model, which corresponds to the Perlmutter model with the cosmological constant. Testing with the Knop and Tonry SN Ia samples show no significant differences.

astro-ph↗

arXiv2003

Dark energy and global rotation of the Universe

We discuss the problem of universe acceleration driven by global rotation. The redshift-magnitude relation is calculated and discussed in the context of SN Ia observation data. It is shown that the dynamics of considered problem is equivalent to the Friedmann model with additional non-interacting fluid with negative pressure. We demonstrate that the universe acceleration increase is due to the presence of global rotation effects, although the cosmological constant is still required to explain the SN Ia data. We discuss some observational constraints coming from SN Ia imposed on the behaviour of the homogeneous Newtonian universe in which matter rotates relative local gyroscopes. In the Newtonian theory $Ω_{\text{r},o}$ can be identified with $Ω_{ω,0}$ (only dust fluid is admissible) rotation can exist with $Ω_{\text{r},0}=Ω_{ω,0} \le 0$. However, the best-fit flat model is the model without rotation, i.e., $Ω_{ω,0}=0$. In the considered case we obtain the limit for $Ω_{ω,0}>-0.033$ at 1σ$ level$. We are also beyond the model and postulate the existence od additional matter which scales like radiation matter and then analyse how that model fits the SN Ia data. In this case the limits on rotation coming from BBN and CMB anisotropies are also obtained. If we assume that the current estimates are $Ω_{\text{m},0}\sim 0.3$, $Ω_{\text{r},0} \sim 10^{-4}$, then the SN Ia data show that $Ω_{ω,0} \ge -0.01$ (or $ω< 2.6 \cdot 10^{-19} \text{rad}/\text{s}$). The statistical analysis gives us that the interval for any matter scaling like radiation is $Ω_{\text{r},0} in (-0.01, 0.04)$.

astro-ph↗

arXiv2002

Brane universes tested by supernovae

We discuss observational constrains coming from supernovae Ia \cite{Perlmutter99} imposed on the behaviour of the Randall-Sundrum models. In the case of dust matter on the brane, the difference between the best-fit general relativistic model with a $Λ$-term \cite{Perlmutter99} and the best-fit brane models becomes detectable for redshifts $z > 0.6$. It is interesting that brane models predict brighter galaxies for such redshifts which is in agreement with the measurement of the $z = 1.7$ supernova \cite{Riess01} and with the New Data from the High Z Supernovae Search Team \cite{schmit02}. We also demonstrate that the fit to supernovae data can also be obtained, if we admit the "super-negative" dark energy $p = - (4/3) \varrho$ on the brane, where the dark energy in a way mimics the influence of the cosmological constant. It also appears that the dark energy enlarges the age of the universe which is demanded in cosmology. Finally, we propose to check for dark radiation and brane tension by the application of the angular diameter of galaxies minimum value test.

astro-ph↗