Test Vector Fields in Inflationary Cosmology

The inflationary epoch in the early universe provides a compelling solution to fundamental cosmological puzzles such as the horizon, flatness, and entropy problems. Although scalar fields have traditionally been the primary focus of inflationary studies, the role of vector fields in this framework has gained increasing interest due to their potential implications for cosmic anisotropies, primordial perturbations, magnetogenesis, and dark matter. This thesis explores the behavior of test massive vector fields during inflation, analyzing their evolution, mode decomposition, and power spectra. By solving the equations of motion for both transverse and longitudinal modes, we investigate their analytical and numerical solutions in the de Sitter regime (as an approximation of inflation), followed by a radiation-dominated era. Our findings contribute to ongoing efforts to extend inflationary models beyond the standard scalar-field paradigm, shedding light on the possible imprint of vector fields in early-universe physics.