Vector-like quark interpretation of excess in Higgs signal strength

Kingman Cheung,Wai-Yee Keung,Jae Sik Lee,Po-Yan Tseng

doi:10.1016/j.physletb.2019.134983

Abstract

There is a +2σ deviation in the average Higgs-signal strength for all the 7+8+13 TeV data up to Summer 2018. We find that a slight reduction of the bottom-Yukawa coupling can fit the data better than the standard model. We suggest an extension with a vector-like quark doublet, of which the right-handed component of b′ mixes nonnegligibly with the standard model b quark. We show that the mixing would induce a reduction of the bottom Yukawa coupling. Simultaneously, the coupling of the Z boson to the right-handed b quark increases, which could reduce the forward-backward asymmetry of bottom production at LEP and bring it closer to the experimental value. However, such a mixing is in tension with the ratio Rb of the partial width Z→bb¯ to the total hadronic width, and with the total hadronic width of the Z boson.

Highlights

The standard model (SM) like Higgs boson was discovered in 2012 [1, 2]
We find that a slight reduction of the bottom-Yukawa coupling can fit the data better than the standard model
We suggest an extension with a vector-like quark doublet, of which the right-handed component of b mixes nonnegligibly with the standard model b quark

Summary

INTRODUCTION

The standard model (SM) like Higgs boson was discovered in 2012 [1, 2]. After Run I at 7 and 8 TeV, the identity of the Higgs boson was very close to the SM one [3, 4]. Component of the bottom quark is reduced and the bottom-Yukawa coupling is reduced with respect to the SM value It can effectively explain why the average Higgs-signal strength is enhanced. The addition of the new vector-like quark doublet can simultaneously explain the Higgs-signal strength μHiggs and the forward-backward asymmetry AbF B in the correspondingly right direction. We describe the extension of an isospin doublet of vector-like quarks, and modifications to the Higgs and Z couplings. We discuss some other potential issues with modifications of the bottom-quark couplings and conclude

FORMALISM

Mass diagonalization and Modifications to Bottom Yukawa

Modifications to the Z couplings

FITTING TO DATA

DISCUSSION