Vacuum polarization is not a precursor for permanent pair creation

The effect of an external charge distribution Q on the Dirac vacuum state has been widely studied. For a small magnitude of Q, it can induce a polarization characterized by the displacement of virtual electrons and positrons. If Q is further increased, the occurrence of real and permanent electron–positron pairs is predicted. These well-known findings might suggest that these two phenomena are just the weak- and strong-field limits of the same dynamical vacuum process. However, a direct comparison of these 'limits' for a charged capacitor configuration shows that this view is incorrect. The physical mechanisms that lead to the formation of the vacuum's induced polarization charges are entirely different from those that trigger the permanent creation of electron–positron pairs. In fact, computational quantum field theory demonstrates that both phenomena can occur independent of each other; a vacuum decay without any significant polarization is possible and vice versa. This finding allows us also to decompose the total charge density at a given location into the respective contributions from the permanent and the polarization charges. (paper)