The origin of the asymmetry between matter and anti-matter of the Universe remains one of the most important open questions in particle physics and cosmology. We propose a novel mechanism, the lepto-bubbles mechanism, to dynamically generate this observed asymmetry. The particle that undergoes the phase transition is a SM-singlet scalar
which couples to the lepton number violating Weinberg dimension-5 operator. The phase transition provides an out of equilibrium condition and the time dependent complex couplings of the scalar to the Weinberg operator are CP-violating. Therefore, the leptobubbles mechanism satisfies Sakharov’s conditions without the introduction of the right-handed neutrinos or the see-saw mechanism. We calculate the lepton asymmetry produced by the phase
transition using the closed time path formalism.