Chiral lagrangians and precision tests of the symmetry breaking sector of the standard model

Abstract

We consider extensions of the minimal Standard Model with various alternatives for the symmetry breaking sector. Different underlying theories are parametrized in terms of the coefficients of a chiral lagrangian. At present and future energies, assuming an exact custodial symmetry in the symmetry breaking sector, all relevant information is contained in just four coefficients. We analyze how to determine these coefficients in the minimal Standard Model with a large Higgs mass, where ordinary perturbation theory is not well suited, and in a class of vector-like technicolor models, but the extension to more general theories is straightforward. We study how to compute radiative corrections in an unambiguous manner and how to extract precise information even if the symmetry breaking sector is described by an effective theory. In doing that we clarify the relationship between the linear and non-linear theories. We apply our techniques to the processes e + e − → ff and e +e − → W +W −, introducing in the latter case an improved Born approximation with a number of phenomenological constants. We identify those processes where it will be possible to unambiguously probe the symmetry breaking sector and compute the full set of one-loop corrections to them in different underlying theories.