Research Projects

Project summary: In summary, our project aims to address the understanding of cosmic structure: its nature in terms of homogeneity, its origin via inhomogeneities and Weyl curvature or gravitational entropy, its impact on the global dynamics of the universe and constraining various cosmological models using the redshift-drift. In 1998 the Supernovae Ia observations disclosed that their discovered luminosity was lower than that of expected and, the deceleration parameter was found to be negative. This negative deceleration parameter suggested the Universe expansion rate is accelerating. It can be explained in a homogeneous universe only by admitting a fluid with negative pressure. Such exotic fluid is named dark energy. Subsequently many dark energy models were proposed but neither one adequately addresses the question of its origin and nature. Also, ΛCDM model cannot explain a few observational phenomena. Though, there have been attempts to explain these observations without any dark energy component. Its key attempts can be widely divided into two categories: inhomogenous models and modified gravity. As it implies, the first category yield the space homogeneity assumption and the second category deals with modified Einstein’s equations. The two inhomogeneous solutions are: Lemaı̂tre-Tolman-Bondi (LTB) models and Szekeres models. There are many LTB models and Szekeres models which claim to explain the cosmological observations without supposing dark energy. This is the reason for proposal of several tests, one of these being the source redshift-drift while the observer’s proper time is elapsing. The redshift drift is a model-independent probe of fundamental cosmology. Cosmological observations usually map our present-day past light cone. Though, it is too possible to equate different past light cones. This is the concept behind the redshift drift, a model-independent probe of fundamental cosmology. It efficiently allows us to watch the Universe expansion in real. As current facilities only allow sensitivities some orders of magnitude worse than the expected signal, it should be possible to detect it with upcoming ones. In our previous papers, redshift- drift was calculated for the axially symmetric Szekeres model and one LTB model which gives appropriate cosmological data that was available , and compared it to the redshift-drift in some LTB models and in the ΛCDM model. In this project, our aim is computing the redshift- drift for all the cosmological models which provide a good fit to data and compare it to the observed value in the future experiments dedicated to the redshift-drift measurement like CODEX/EXPRESSO, SKA and the gravitational waves observations DECIGO/BBO. This will enable us to find the correct model of the universe among all the proposed models which claim to explain the observations.

Redshift-drift, Inhomogeneous models, Cosmological Discriminators, Modified Gravity, Dark energy, Gravitational Entropy