Electroweak symmetry breaking and precision tests with a fifth dimension

Abstract

We perform a complete study of flavour and CP conserving electroweak observables in a slight refinement of a recently proposed five-dimensional model on R 4 × S 1 /Z 2 , where the Higgs is the internal component of a gauge field and the Lorentz symmetry is broken in the fifth dimension.Interestingly enough, the relevant corrections to the electroweak observables turn out to be of universal type and essentially depend only on the value of the Higgs mass and on the scale of new physics, in our case the compactification scale 1/R. The model passes all constraints for 1/R ≥ 4.7 TeV at 90% C.L., with a moderate fine-tuning in the parameters. The Higgs mass turns out to be always smaller than 200 GeV although higher values would be allowed, due to a large correction to the T parameter. The lightest non-SM states in the model are typically colored fermions with a mass of order 1 − 2 TeV.

On the tuning and the mass of the composite Higgs

“…A tuning of order 10% is often believed sufficient to comply with the experimental constraints.However it has been found that the tuning is typically larger in concrete constructions. This has been verified explicitly in 5d holographic models [8,9,10] and explained parametrically in Ref. [11,12].…”

Dark matter and electroweak symmetry breaking in models with warped extra dimensions

“…Hence, we also include these effects in the fit to the EW precision observables, although, for the reasons explained above, we do not include flavor violating effects. 9 In this analysis we have performed a fit to the Z-pole observables and the W mass [33], and include the effects of fourfermion interactions that enter through the Fermi constant (these effects are subdominant). The upshot is that there is a bound of about µ ir ∼ 1.3 TeV in the c u > 0 region, while the c u < 0 region is somewhat more constrained, with a lower bound µ ir ∼ 1.7 TeV.…”

“…A careful estimate of the nuclear matrix element N |QQ|N would require a detailed one-loop analysis, along the lines of [55]. For an order of magnitude estimate, it is however enough to use the old result [56] N |QQ|N = 2 27 9) where f N Tq = N |qq|N m q /m N . It is now straightforward to compute σ scalar .…”

“…The exchange symmetry we advocate has been first introduced in [9] (where it was dubbed "mirror symmetry") and [10] to alleviate the fine-tuning and to get a viable DM candidate in Gauge-Higgs Unification (GHU) models in flat space. As already anticipated in [9], it can be extended straightforwardly to warped models. Given a bulk field, φ, satisfying certain boundary conditions (b.c.…”

Effect of boundary conditions on dimensionally reduced field-theoretical models at finite temperature

“…The construction and use of quantum field theoretical models at dimensions different from the usual space-time in D = 3 + 1 are usual in the literature [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Its first appearance seems to be in the construction of the Kaluza five-dimensional theory [1] that intended to unify gravity and electromagnetism.…”