Higgs Bosons, theory and searches

Understanding the mechanism that breaks electroweak symmetry and generates the masses of all known elementary particles is one of the most fundamental problems in particle physics. The Higgs mechanism [1] provides a general framework to explain the observed masses of the W± and Z gauge bosons by means of charged and neutral Goldstone bosons that end up as the longitudinal components of the gauge bosons. These Goldstone bosons are generated by the underlying dynamics of electroweak symmetry breaking (EWSB). However, the fundamental dynamics of the electroweak symmetry breaking are unknown. There are two main classes of theories proposed in the literature, those with weakly coupled dynamics such as in the Standard Model (SM) [2] and those with strongly coupled dynamics. In the SM, the electroweak interactions are described by a gauge field theory based on the SU(2)L×U(1)Y symmetry group. The Higgs mechanism posits a self-interacting complex doublet of scalar fields, and renormalizable interactions are arranged such that the neutral component of the scalar doublet acquires a vacuum expectation value v ≈ 246 GeV, which sets the scale of EWSB. Three massless Goldstone bosons are generated, which are absorbed to give masses to the W± and Z gauge bosons. The remaining component of the complex doublet becomes the Higgs boson a new fundamental scalar particle. The masses of all fermions are also a consequence of EWSB since the Higgs doublet is postulated to couple to the fermions through Yukawa interactions. If the Higgs boson mass mH is below ∼ 180 GeV, all fields remain weakly interacting up to the Planck scale, MPl. The validity of the SM as an effective theory describing physics up to the Planck scale is questionable, however, because