Minimum Virtual Proper Time and Finite Mass--Charge Matching in QED

Abstract: We formulate a finite-proper-time version of QED defined by a gauge-covariant generating functional in which every Schwinger proper-time integral has a physical lower endpoint $s_0=Λ^{-2}$ that is not removed. Closed fermion loops are defined by the gauge-covariant heat-kernel determinant, and open fermion lines are obtained by functional differentiation of the same finite-proper-time open-line kernel. The Ward--Takahashi identity follows exactly from gauge covariance to all orders. The vacuum polarisation is finite and exactly transverse. The on-shell mass relation gives 0.482$$ MeV for an illustrative choice $Λ=13\$ TeV at one loop. The free finite-proper-time propagators are proved to satisfy Osterwalder--Schrader reflection positivity, with a positive Kallen--Lehmann spectral function and no additional ghost states. The on-shell residue $Z_2>0$ at one loop confirms unitarity of the fermion sector, and the perturbative spectral function of the dressed propagator is positive. A worldline bound $Q\le0$ gives fixed-order Euclidean UV finiteness. The one-loop vertex correction gives a finite anomalous magnetic moment, a calculable $O(m^2/Λ^2)$ prediction absent in standard QED.