Radiative electroweak symmetry breaking in a Little Higgs model

Abstract

We present a new Little Higgs model, motivated by the deconstruction of a fivedimensional gauge-Higgs model. The approximate global symmetry is SO(5) 0 × SO(5) 1 , breaking to SO(5), with a gauged subgroup of [SU (2) 0L × U (1) 0R ] × O(4) 1 , breaking to SU (2) L × U (1) Y . Radiative corrections produce an additional small vacuum misalignment, breaking the electroweak symmetry down to U (1) EM . Novel features of this model are: the only un-eaten pseudo-Goldstone boson in the effective theory is the Higgs boson; the model contains a custodial symmetry, which ensures thatT = 0 at tree-level; and the potential for the Higgs boson is generated entirely through one-loop radiative corrections. A small negative mass-squared in the Higgs potential is obtained by a cancellation between the contribution of two heavy partners of the top quark, which is readily achieved over much of the parameter space. We can then obtain both a vacuum expectation value of v = 246 GeV and a light Higgs boson mass, which is strongly correlated with the masses of the two heavy top quark partners. For a scale of the global symmetry breaking of f = 1 TeV and using a single cutoff for the fermion loops, the Higgs boson mass satisfies 120 GeV M H 150 GeV over much of the range of parameter space. For f raised to 10 TeV, these values increase by about 40 GeV. Effects at the ultraviolet cutoff scale may also raise the predicted values of the Higgs boson mass, but the model still favors M H 200 GeV.

Constraining fine tuning in composite Higgs models with partially composite leptons

“…One must also make the theory reproduce a variety of observations including the Higgs VEV, the Higgs mass and the fermion masses, each of which can in principle contribute an independent source of fine tuning. It is known, for example, that the Higgs mass is specifically correlated with the mass of the lightest top partner for certain choices of the embedding of the composite states in SO(5) [10][11][12][16][17][18][19][20], making light top partners essential for naturalness in these models.…”

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

“…Using the basis for the ten SO(5) generator matrices, given in the Ref. [6], we can specify the goldstone boson fields as…”

“…[6], these Yukawa terms, along with the Dirac masses of Eq. (17), maintain the collective symmetry breaking necessary for the Little Higgs mechanism.…”

“…In a recent paper [6], we presented a Little Higgs model, based on the approximate SO(5) × SO(5) global symmetry, of which an SU (2) 3 × U(1) subgroup is gauged. In that paper we emphasized the unique feature of the model that the potential for the Higgs boson can be generated entirely through one-loop radiative corrections, and gives rise to a relatively light Higgs boson (M H 200 GeV) even after effects at the UV cutoff scale are included.…”

“…[6] on universal electroweak corrections by allowing a more general set of gauge parameters. In addition, we consider the contributions to the ZW W triple-gauge-boson vertex.…”