Cosmological Parametrization: A Model-Independent approach in Cosmological Modelling and Reconstructing Cosmic Evolution

Speaker: Dr. Shibesh Kumar Jas Pacif, Thanu Padmanabhan Centre for Cosmology, SGT University, Haryana, India

Gravity best describes the large-scale structure of the Universe and Einstein general theory of relativity is the most successful theory till date even though axed so many times in its journey of hundred years. After the formulation of Einstein Field Equations (EFEs), the task is to solve the system of equations, which are complicated set of ordinary differential equations. The discovery of cosmic acceleration brought a paradigm shift in recent times. In Einstein’s theory, an extra degree of freedom has to be incorporated in the matter sector in order to explain the late-time acceleration. With this extra degree of freedom (dubbed dark energy) in EFEs, one more variable comes into picture and in order to make the system consistent, one more equation is needed besides the equation of state of ordinary and cold dark matter. This extra equation can be chosen in a model-independent way i.e. by parametrizing any physical or geometrical parameter involved in the field equations. Since, the nature of dark energy is a mystery; there is freedom to choose the equation of state (EoS) in different functional forms such as Polytropic gas, logotropic gas, van der Waals gas equation of state etc. Similarly, there is some freedom to choose the functional form of physical of geometrical parameters mathematically (generally termed as cosmological parametrization). The assumption does not violate the background physics rather provide a simple mathematical way to reconstruct the cosmic evolution. In the past few decades, a number of functional forms of various cosmological parameters have been considered for obtaining a consistent solution of the EFEs. In this talk, the idea of the model independent approach to the cosmological parametrization will be discussed in some detail.