The precision electroweak data in warped extra-dimension models

TL;DR

This paper investigates how warped extra-dimension models with custodial symmetry can address electroweak precision data anomalies, improve fits to experimental results, and predict new particles accessible at the LHC.

Contribution

It identifies minimal quark representations in Randall-Sundrum models that reconcile anomalies and electroweak data, including detailed corrections to Zbb couplings and phenomenological implications.

Findings

Improved fit to electroweak precision data with KK masses of 3-5 TeV.

Heavy Higgs masses up to ~500 GeV are compatible with data.

Potential discovery of light custodial partners like b' at the LHC.

Abstract

The Randall-Sundrum scenario with Standard Model fields in the bulk and a custodial symmetry is considered. We determine the several minimal quark representations allowing to address the anomalies in the forward-backward b-quark asymmetry A^b_FB, while reproducing the bottom and top masses via wave function overlaps. The calculated corrections of the Zbb coupling include the combined effects of mixings with both Kaluza-Klein excitations of gauge bosons and new b'-like states. It is shown that the mechanism, in which the left-handed doublet of third generation quarks results from a mixing on the UV boundary of introduced fields Q_1L and Q_2L, is necessary for phenomenological reasons. Within the obtained models, both the global fit of R_b with A^b_FB [at the various center of mass energies] and the fit of last precision electroweak data in the light fermion sector can simultaneously be improved significantly with respect to the pure Standard Model case, for M_KK = 3,4,5 TeV (first KK gauge boson) and a best-fit Higgs mass m_h > 115 GeV i.e. compatible with the LEP2 direct limit. The quantitative analysis of the oblique parameters S,T,U even shows that heavy Higgs mass values up to ~500 GeV may still give rise to an acceptable quality of the electroweak data fit, in contrast with the Standard Model. The set of obtained constraints on the parameter space, derived partly from precision electroweak data, is complementary of a future direct exploration of this parameter space at the LHC. In particular, we find that custodians, like b' modes, can be as light as ~1200 GeV i.e. a mass lying possibly in the potential reach of LHC.