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 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.