  The spontaneous baryogenesis scenario explains how a baryon asymmetry can
develop while baryon violating interactions are still in thermal equilibrium.
However, generation of the chemical potential from the derivative coupling is
dubious since the chemical potential may not appear after the Legendre
transformation. The geometric phase (Pancharatnam-Berry phase) results from the
geometrical properties of the parameter space of the Hamiltonian, which is
calculated from the Berry connection. In this paper, using the formalism of the
Berry phase, we show that the chemical potential defined by the Berry
connection is consistent with the Legendre transformation. The framework of the
Berry phase is useful in explaining the mathematical background of the
spontaneous baryogenesis, and also is useful for calculating the asymmetry of
the non-thermal particle production in time-dependent backgrounds. Using the
formalism, we show that the mechanism can be extended to more complex
situations.
