New constraint on a strongly interacting Higgs sector.

We show that an integral S over the spectral function of spin-l states of the Higgs sector is constrained by precision weak-interaction measurements. Current data excludes large technicolor models; experiments at LEP and ‘SLC will sooi provide more stringent limits on Higgs strong interactions. Submitted to Physical Review Letters PACS numbers: 12.15.Cc, 12.15.Ji, 14.80.Er * Work supported by the Department of Energy, contract DE-AC0346SF00515. The most pressing question in the study of weak interactions is the nature of the Higgs sector. In the standard SU(2) x U(1) theor o weak interactions, some new y f particle or set of forces is needed to break the gauge symmetry. However, models of these Higgs particles ranging from a minimal doublet of scalar-fields to elaborate models with a rich spectrum are still consistent with experiment. We do not even know whether the new sector is weakly interacting, containing fundamental scalar fields and symmetry-breaking forces visible in perturbation theory, or whether it is strongly interacting, so that the symmetry-breaking results from nonperturbative ~-. phenomena. Beyond the fact that the Higgs sector does break SU(2) x U(1) in the required way, the main nontrivial piece of information that we have about its nature comes from the precision study of weak interaction parameters. [‘I T he relation12’ between the W and 2’ masses and the value of the weak mixing angle sin2 6, rn2,/rni cos2 6, 2 1 , to about l%, implies that the Higgs sector h&s an approximate global SU(2) ‘cG [31 todial’ symmetry. Depending on the exact definition used to compute sin2 8,, the violation of the relation (1) measures the SU(2) y s mmetry violation in the Higgs sector. In this letter, we will extend this conclusion to demonstrate that precision weak interaction experiments also constrain an isospin-symmetric observable of the Higgs sector. In essence, we will show that, by comparing weak interaction parameters, one can constrain not only the isospin asymmetry of this sector but also its total size. A longer and more complete version of this argument will be presented in ref. 4. Our analysis will be based on the general formalism for weak interaction radiative corrections presented in refs. 5 and 6. This work begins from the observation that radiative corrections to weak-interaction processes involving light quarks and leptons due to new physics beyond the standard model appears dominantly through