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 construct ing 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 utilizes the DESI and Pantheon datasets to guide itself and constrain the model’s parameters. An initial AIC/BIC com parison against a ”test” version of the model suggests that the quintessence framework outperforms ΛCDM in both criterion. In addition, the quintessence model simplifies to the ΛCDM model at a scale factor of a = 0.75, the beginning of the dark energy-dominated era, which was also determined by the test case. Finally, the results indicate that the final quintessence model accurately repro duces the cosmological epochs and predicts a value for the Hubble parameter of H0 = 76.524+2.5114-4.1723 km/s/Mpc. Due to limited resources, the MCMC had to restrict the full datasets, and in turn utilized random sampling methods. As a result, further research will be done with more powerful computational resources.