Speaker
Description
Our study investigates the impact of decaying string axions on the cosmic reionization history. Axions decay produces ionizing photons that modify the ionization fraction of the intergalactic medium, introducing an additional contribution to the total optical depth. By analyzing the optical depth constraints from the Cosmic Microwave Background (CMB), we derive stringent limits on the parameter space of string axion models, including the maximum allowable reheating temperature for different string axion models.
Furthermore, we develop and apply a Gaussian-Process (GP)–driven reionization scheme method to reconstruct the CMB optical depth in a model-independent framework, leveraging observational data to obtain a robust posterior distribution. This posterior is then utilized to impose general constraints on the axion parameter space, significantly refining previous bounds.
