Gauge-Higgs unification and radiative electroweak symmetry breaking in warped extra dimensions

Abstract

We compute the Coleman Weinberg effective potential for the Higgs field in RS Gauge-Higgs unification scenarios based on a bulk SO(5) × U (1) X gauge symmetry, with gauge and fermion fields propagating in the bulk and a custodial symmetry protecting the generation of large corrections to the T parameter and the coupling of the Z to the bottom quark. We demonstrate that electroweak symmetry breaking may be realized, with proper generation of the top and bottom quark masses for the same region of bulk mass parameters that lead to good agreement with precision electroweak data in the presence of a light Higgs. We compute the Higgs mass and demonstrate that for the range of parameters for which the Higgs boson has Standard Model-like properties, the Higgs mass is naturally in a range that varies between values close to the LEP experimental limit and about 160 GeV. This mass range may be probed at the Tevatron and at the LHC. We analyze the KK spectrum and briefly discuss the phenomenology of the light resonances arising in our model. High energy physics experiments in recent years have confirmed the predictions of the Standard Model (SM), a renormalizable, chiral gauge theory based on the group SUIn particular, the low energy dynamics of fermions and gauge bosons of the theory have been tested with great accuracy. The origin of masses of these fundamental particles, however, remains a mystery. In the SM, masses arise through the vacuum expectation value (vev) of a scalar field doublet, which spontaneously breaks the electroweak (EW) symmetryA physical, neutral scalar field, the so called Higgs field, appears in the spectrum. Information on the mass of this scalar particle may be obtained through the quantum corrections that it induces to the masses and couplings of the EW gauge bosons. Consistency of the SM predictions with experimental observations is improved for small values of the Higgs mass, m H , close to the current experimental bound, m H ≥ 114.4 GeV [1].There are several aspects of the mechanism of the origin of mass that demand explanation. On one hand, the scale of the spontaneous symmetry breaking is governed by the size of the scalar mass parameter appearing in the Higgs field effective potential, and is much smaller than the Planck scale, the only known mass scale in nature, besides the dynamical generated QCD scale Λ QCD . Moreover, this scale is associated with a negative value of the squared Higgs mass. There is, however, no dynamical explanation for the origin of the Higgs effective potential, or for the associated breakdown of the EW symmetry. Finally, the hierarchy of the fermion masses of the different generations remains unexplained.Warped extra dimensions provide a theoretically attractive framework for the solution of the hierarchy problem of the SM. For one extra spatial dimension as in RS1 [2], the curvature k in the extra dimension induces a warp factor on the four dimensional metric, which depends on the position in the extra dimension. The coordinate point, x 5 = 0, is associated with a t...

Radion/dilaton-Higgs mixing phenomenology in light of the LHC

“…Thus the linear radion coupling to the electroweak gauge boson mass terms vanishes in the case of a bulk Higgs. This result can also be checked by simply expanding the metric in its spin-0 fluctuations in the matter action 5) where the index on the r.h.s. is contracted using the Minkowski metric.…”

“…Though it is protected by the gauge symmetry at tree-level, it acquires a potential at loop level that successfully leads to electroweak symmetry breaking (EWSB) and provides a light Higgs mass protected from the UV-physics [4,5]. Due to the AdS/CF T correspondence and through the language of holography, it was realized that these kinds of models are particular realizations of composite Higgs scenarios where the Higgs is a PNGB arising from the spontaneous breaking of a global shift symmetry G, and where SM particles have a degree of compositeness determined by their coupling to operators that reside in the conformal sector.…”

5D perspective on Higgs production at the boundary of a warped extra dimension

“…The fermion representations we adopt are chosen such that they can be embedded into complete SO(5) multiplets used in the context of models with gauge-Higgs unification [31,32,56]. As a consequence of the discrete P LR symmetry, which is instrumental in protecting the left-handed Zbb coupling [28] and its flavor-changing counterparts [11], the left-handed bottom quark has to be embedded in a SU(2) L × SU(2) R bi-doublet with isospin quantum numbers T 3 L = −T 3 R = −1/2.…”

Alternatives to an elementary Higgs

“…As in "little" Higgs models, the electroweak gauge symmetry is embedded in a larger global symmetry which is broken at a strong interaction scale f ∼ 1 TeV, producing a Goldstone boson that is identified with the SM Higgs, for reviews see Grojean (2009), Contino (2011, Rychkov (2011), Espinosa et al (2012a), Bellazzini et al (2014) and Panico and Wulzer (2016) . In an extra dimensional setting 6 these models are also referred to as gauge-Higgs unification (Csáki et al, 2003a;Medina et al, 2007;Panico et al, 2006;Serone, 2010) since the Goldstone boson shows up as the fifth component of a bulk gauge field. The effective theory has a cutoff Λ ∼ 4πf ∼ 5-10 TeV.…”