Role of universal and nonuniversal Sudakov logarithms in four-fermion processes at TeV energies: The one-loop approximation reexamined

We consider the separate effects on four-fermion processes, in the TeV energy range, produced at one loop by Sudakov logarithms of universal and nonuniversal kind, working in the ’t Hooft $\xi =1\mathrm{}$ gauge. Summing the various vertex and box contributions allows us to isolate two quite different terms. The first one is a combination of vertex and box quadratic and linear logarithms that are universal and independent of the scattering angle $\theta .$ The second one is $\theta$ dependent, not universal, linearly logarithmic, and produced only by weak boxes. We show that for several observables, measurable at future linear $e^{+}{e}^{-}$ colliders, the role of the latter term is dominant, and we discuss the implications of this fact for what concerns the reliability of a one-loop approximation.