A “Littlest Higgs” Model with Custodial SU(2) Symmetry

In this note, a “littlest higgs” model is presented which has an approximate custodial SU(2) symmetry. The model is based on the coset space SO(9)/(SO(5)×SO(4)). The light pseudo-goldstone bosons of the theory include a single higgs doublet below a TeV and a set of three SU(2)W triplets and an electroweak singlet in the TeV range. All of these scalars obtain approximately custodial SU(2) preserving vacuum expectation values. This model addresses a defect in the earlier SO(5)× SU(2)×U(1) moose model, with the only extra complication being an extended top sector. Some of the precision electroweak observables are computed and do not deviate appreciably from Standard Model predictions. A wide range of higgs masses is allowed in a large region of parameter space consistent with naturalness.