AR-2020-21

271 33 rd ANNUAL REPORT 2020-21 Department of Physics, Cochin University of Science and Technology, Kochi (Coordinator: Titus K. Mathew, and Co-coordinator: Charles Jose) Areas of Research Publications using ICARD Facilities · Dark Energy Models · Emergent Gravity Paradigm · Cosmological Structure Formation Holographic Ricci dark energy evolving through its interaction with dark matter is a natural choice for the running vacuum energy model.We have analyzed the relative significance of two versions of this model in the light of SNIa, CMB, BAO and Hubble data sets using the method Bayesian inferences. The first one, model 1, is the running holographic Ricci dark energy (rhrde) having a constant additive term in its density form, and the second one is, model 2, having no additive constant, instead the interaction of rhrde with dark matter is accounted through a phenomenological coupling term. The Bayes factor of these models in comparison with the standard Λ CDM have been obtained by calculating the likelihood of each model for four different data combinations, SNIa (307) + CMB + BAO, SNIa (307) + CMB+ BAO + Hubble data, SNIa (580) + CMB + BAO, and SNIa (580) + CMB + BAO + Hubble data. Suitable flat priors for the model parameters has been assumed for calculating the likelihood in both cases. Our analysis shows that, according to the Jeffreys scale, the evidence for Λ CDM against both is very strong as the Bayes factor of bothmodels aremuch less than one for all the data combinations. The special expansion of the universe could be described as a tendency for satisfying holographic equipartition, which inevitably demands the presence of dark energy. We explore whether this novel idea proposed by Padmanabhan give any additional insights into the nature of dark energy. In particular, we obtain the constraints imposed by the law of emergence on the equation of state parameter, ω . We also present a thermodynamic motivation for the obtained constraints on ω . Further, we explicitly prove the feasibility of describing a dynamic dark energy model through the law of emergence. Interestingly, both holographic equipartition and the entropy maximization demands an asymptotically de Sitter universe with ω ≥ −1, rather than a pure cosmological constant. Structure formation in cosmology is still an active area of research and has been made considerable progress in this field. · P.B. Krishna, and Titus K. Mathew (2020) Does holographic equipartition demand a pure cosmological constant?, MPLA, 35(40), 2050334.