Series expansion of the quark determinant in the number of quark-antiquark pairs

We propose a formulation of the QCD partition function which leads to a series expansion of the quark determinant in any given baryonic sector. The r-th term gives the gauge-invariant contribution of the valence quarks plus r quark-antiquark pairs. This expansion can be used to investigate any baryonic sector, starting from the nucleon up to high baryonic densities.