Theoretical considerations concerning the Z0 mass.

Abstract

We compare two previously introduced theoretical definitions of the ${\mathit{Z}}^{0}$ mass and show that one of them, frequently used, is gauge dependent in O(${\mathrm{\ensuremath{\alpha}}}^{3}$) in a wide class of gauges and in O(${\mathrm{\ensuremath{\alpha}}}^{2}$) in the complementary class. We then discuss a slightly modified version that circumvents these problems, is endowed with desirable theoretical properties, and can be identified with the mass measured at the CERN ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ collider LEP. The simple formulation that emerges is applied to illustrate properties of the physical amplitude, related to gauge invariance, and the role played by the two definitions of mass.