A different perspective on the vev insertion approximation for electroweak baryogenesis

Understand

In the vev insertion approximation (VIA) the spacetime dependent part of the mass matrix is treated as a perturbation.

• We calculate the source terms for baryogenesis expanding both the self-energy and propagator to first order in mass insertions, which gives the same results as the usual approach of calculating the self-energy at second order and using zeroth order propagators.
• This procedure shows explicitly the equivalence between including the mass in the free or in the interaction Lagrangian.
• The VIA source then originates from the same term in the kinetic equation as the semi-classical source, but at leading order in the derivative expansion (the expansion in diamond operators).