Post-Inflationary Cosmological Dynamics Governed by Evolving Quintessence Fields

This study presents an alternative cosmological framework for the ΛCDM model by proposing a dynamic quintessence scalar field as a substitute for the cosmological constant. Instead of constructing this model from existing theories, it takes a phenomenological approach to model the expansion history of the universe. This mathematical framework is centered around the modified version of the first Friedmann equation for this quintessence model. It is plugged into a Markov Chain Monte Carlo (MCMC) algorithm to determine the posterior parameter distributions of our model, which will be used to map the evolution of different cosmological components and reconstruct the various epochs of cosmological history. During the MCMC analysis, the algorithm utilized the DESI and Pantheon datasets to guide itself and constrain the model’s parameters. The results indicate that the quintessence model accurately reproduces the cosmological epochs and predicts a value for the Hubble parameter of H0 = 70.2239 (+6.5223) (-6.6520) km/s/Mpc. In addition, the quintessence model simplifies to the ΛCDM model at a scale factor of a = 0.74, the beginning of the dark energy-dominated era. However, this analysis lacks computational power; due to limited resources, the MCMC was run on CPUs rather than GPUs, restricting the full datasets and, in turn, requiring random sampling. As a result, further research will be done with more powerful computational resources.