Holographic pseudo-Goldstone boson

The LHC experiment will soon probe how W and Z bosons acquire their masses. So far we have only indirect hints about the actual mechanism of electroweak symmetry breaking. The standard model (SM) introduces a weakly coupled fundamental scalar field—the Higgs field— whose condensation breaks the electroweak symmetry. This simple picture is consistent with precision electroweak measurements, if the mass of the Higgs boson is * 100 GeV and the SM cutoff is far above a TeV. However, from a theoretical point of view, a fundamental scalar much lighter than the theory’s cutoff is unnatural, unless there is a symmetry protecting its mass. Perhaps the most elegant realization of the Higgs sector is the one in which the Higgs field is composite, rather than fundamental [1]. This can be achieved by introducing a new strongly interacting sector with a global symmetry G GSM. In this scenario the Higgs field is a pseudoGoldstone boson arising from a spontaneous breaking of G. The global symmetry could be broken by a condensate, in close analogy with chiral symmetry breaking in QCD. If the condensate leaves the SM gauge symmetry intact, the effective theory below the compositeness scale of the new strong interactions includes the SM fields coupled to a nonlinear sigma model field describing the pseudoGoldstone Higgs. The Higgs field has a flat potential at tree level, but a nontrivial potential can be generated through its couplings to the SM that do not respect the full global symmetry. In such framework, we expect the Higgs potential of the form