Can phase transitions in the early Universe induce B mode polarization?

We investigate the potential for tensor perturbations from first-order phase transitions occurring in the early universe after inflation to generate detectable B-mode polarization in the CMB. Our analysis reveals that while such phase transitions can produce gravitational waves, the amplitude of the resulting B-mode signal may be significantly suppressed due to the expansion of the universe. This suppression challenges the detectability of B-modes from phase transitions with current observational capabilities. We discuss the implications of this finding for alternative sources of B-mode polarization and suggest directions for future research to overcome these challenges.