  The study of the universe's primordial plasma at high temperature plays an
important role when tackling different questions in cosmology, such as the
origin of the matter-antimatter asymmetry. In the Minimal Standard Model (MSM)
neither the amount of CP violation nor the strength of the phase transition are
enough to produce and preserve baryon number during the Electroweak Phase
Transition (EWPT), which are two of the three ingredients needed to develop
baryon asymmetry. In this talk we present the first part of the analysis done
within a scenario where it is viable to have improvements to the aforementioned
situation: we work with the degrees of freedom in the broken symmetry phase of
the MSM and analyze the development of the EWPT in the presence of a weak
magnetic field. More specifically, we calculate the particle self-energies that
include the effects of the weak magnetic field, needed for the MSM effective
potential up to ring diagrams.
