Constraints on a little Higgs model with fully radiative electroweak symmetry breaking

Abstract

In a recent paper, we introduced a new Little Higgs model, which contains the gauge structure SU (2) 3 × U (1), embedded in an approximate global SO(5) × SO(5) symmetry. After breaking to the standard model, SU (2) L × U (1) Y , this produces two heavy Z ′ bosons and two heavy W ′± bosons, along with a single Standard Model-like Higgs scalar. The unique feature of the model was that it was possible to obtain electroweak symmetry breaking and a light Higgs mass entirely from perturbative loop contributions to the Higgs effective potential. In this paper we consider the electroweak constraints on this model, including tree and loop contributions to the universal oblique and non-oblique parameters, tree-level corrections to the ZW W vertex, and tree and loop level corrections to Zbb. The most significant corrections are positive tree-level corrections toŜ and negative fermion-loop corrections toT , which require that the scale for the global symmetry breaking be 2 TeV, depending on the top-quark mixing parameter and the extra gauge couplings.In addition, the loop corrections to Zbb contain a divergence that must be absorbed into the coefficient of a new operator in the theory. The finite part of this Zbb correction, however, is negligible. *

Stabilizing electroweak vacuum in a vectorlike fermion model

“…The presence of vertex corrections gives rise to non-zero δg NP L . To extract out the leading m T -dependent terms explicitly, we perform the loop calculation in the "gaugeless" limit [31][32][33][34], in which the Z boson is treated as a non-propagating external field coupled to the current J µ =b L γ µ b L . Using the Wald identity [31,32], the leading contribution to the Zb LbL coupling can be obtained via the calculation of the higher dimensional operator ∂µπ 0 m Zb L γ µ b L , where π 0 is the Goldstone boson eaten by the Z boson.…”