Fig. 4: Physical picture of the field correlations.
a Conceptual representation of the local processes contributing to the zeroth-order of correlations (\({{{{{{{{\mathcal{S}}}}}}}}}_{0,0}\)). b Depiction of the non-local processes giving rise to the \({{{{{{{{\mathcal{S}}}}}}}}}_{1,1}\) contribution to the second-order of correlations. c Contribution \({{{{{{{{\mathcal{S}}}}}}}}}_{0,2}\) to the second-order of correlations. The two planes at ρz and \({\rho }_{z}^{{\prime} }\) separate different regions to distinguish among the possible cases that may occur. Red, green, and blue colors represent zeroth, first, and second order features (fields, currents, or propagators), respectively.
