Chiral Lagrangians as a tool to probe the symmetry-breaking sector of the SM at LEP

Abstract

An effective SU(2)L X U(1)Y invariant chiral lagrangian can accommodate any symmetry breaking scheme in the standard model. It is shown that all process-independent quantities relevant to LEP precision measurements (DELTA-rho, DELTA-K and DELTA-r) depend only on one coefficient of the weak chiral lagrangian, taking different values depending on the precise symmetry breaking scheme. We remove any ambiguity due to the use of an effective theory by a careful choice of observables and make definite predictions that can be tested in the foreseeable future. Our analysis complements nicely that of longitudinal W and Z scattering.