Top Forward-backward asymmetry at the Tevatron vs. Charge asymmetry at the LHC in chiralU(1)’ models with flavored Higgs fields P.

P Ko,Chaehyun Yu,Yuji Omura

doi:10.1051/epjconf/20134917005

Abstract

An extra $U(1)'$ model with $Z'$ coupled only to the right-handed (RH) up-type quarks has been one of the popular models for the Tevatron top forward-backward asymmetry (FBA), and has been excluded by the same-sign top-pair productions at the LHC. However, the original $Z'$ model is not physical, since the up-type quarks are massless including the top quark. This disaster can be evaded if the Higgs sector is extended by including new Higgs doublets with nonzero $U(1)'$ charges. We find that some parameter regions could achieve not only the top FBA at the Tevatron, but also the charge asymmetry at the LHC without exceeding the upper limit of the same-sign top-quark pair production at the LHC. The lesson is that it is mandatory to extend the Higgs sector whenever one considers chiral gauge symmetries beyond the SM gauge group. Otherwise some fermions remain massless, and thus it is meaningless to work on phenomenology without the extra Higgs doublets with new chiral gauge charges.

Highlights

The top forward-backward asymmetry (AtFB) is one of the most interesting observables because there exists discrepancy between theoretical predictions in the standard model (SM) and experimental results at the Tevatron
If the discrepancy in AtFB is generated by new physics, the new physics model would be tested at the LHC
A lot of new physics models have been introduced to account for this deviation

Summary

Introduction

The top forward-backward asymmetry (AtFB) is one of the most interesting observables because there exists discrepancy between theoretical predictions in the standard model (SM) and experimental results at the Tevatron. The number of additional Higgs doublets depends on the U(1)′ charge assignment to the SM fermions, especially the right-handed up-type quarks. The number of relevant Higgs bosons participating in the top-quark pair production depends on the U(1)′ charge assignment and mixing angles. For example the Yukawa couplings of the neutral scalar bosons h, H, a have flavor changing couplings to the uptype quarks because of the flavor non-universal nature of Z′ interaction [12]: Ythu. FBA and the same-sign top-pair productions are generated by the t-channel Z′ exchange, and by the tchannel exchange of neutral Higgs scalars, and the strong constraint on the original Z′ model from the same-sign top-pair production can be relaxed by a significant amount when we include all the contributions in the model, as described

Generalities and Inputs

Findings

Summary