HIGGS-BOSON LOW-ENERGY THEOREM AND COMPATIBLE GAUGE-FIXING CONDITIONS

Conventional gauge-fixing schemes such as R-xi gauges may lead to a vi olation of the Higgs-boson low-energy theorem beyond the tree level. T o elucidate this fact, we study a simple model whose U(I) gauge symmet ry is spontaneously broken, and show how the Higgs-boson low-energy th eorem can consistently be extended to the gauge and Higgs sectors of t he model. In this formulation, any gauge-fixing condition must comply with the requirement that it should be independent of the vacuum expec tation value of the Higgs field in the symmetric limit of the theory. We give a diagrammatic proof of the Higgs-boson low-energy theorem to all orders in perturbation theory, within the context of a judiciously modified R-xi gauge compatible with the above constraint. The depende nce of the kinematic parameters on the Higgs tadpole is found to be ve ry important for the proof of the theorem. (C) 1998 Elsevier Science B .V.