Explaining the $R_{K^{(*)}}$ anomalies in a Fundamental Composite Higgs Model with Gauged $U(1)_{SM_3-HB}$

Abstract

A new heavy $Z'$ vector boson provides a possible explanation for the neutral current B anomalies. Various $U(1)'$ gauge groups have been proposed and studied. In this paper, we explore a new type of $U(1)'$ gauge symmetry inspired by fundamental composite Higgs models with hyperfermions. It is also the first attempt to connect such a $Z'$ boson with a solution to the hierarchy problem. The $U(1)'$ symmetry is identified as the quantum number of the difference between the Standard Model fermion number and hyperbaryon number, written as $SM-HB$. This type of $U(1)'$ gauge symmetry is naturally broken in some fundamental composite Higgs models, which leads to a TeV-scale $Z'$ boson. We present a concrete example based on the minimal fundamental composite Higgs model with $SU(4)/Sp(4)$ coset, where the $Z'$ boson is the only state below the compositeness scale beside the composite Higgs. We also show that if the $U(1)'$ symmetry is third-generation-philic, written as $SM_3-HB$, the corresponding $Z'$ boson can explain the neutral current B anomalies. The model introduces the composite Higgs and the $Z'$ boson from the same symmetry breaking scale, so Higgs physics and flavor physics are now connected. After considering all the experimental constraints and theoretical preferences, we found that there is still a natural parameter space for $SU(4)/Sp(4)$ fundamental composite Higgs model with $N_{HC}=2$, which can be probed in the near future.