Unification of the electroweak and horizontal interactions

Gye Tai Park, Purdue University

Abstract

For three generations of fermions, SP(6) $\times$ U(1) is proposed as the flavor gauge group which unifies the electroweak and horizontal interactions. The model suggests the existence of additional light left-handed horizontal gauge bosons W$\sp\prime$ and Z$\sp\prime$. We examine a class of extended electroweak models in which quark flavors are violated due to neutral gauge bosons which do not couple universally to the fermion generations. It is shown that the decays Z$\sp0$ $\to$ bs + sb and Z$\sp0$ $\to$ tc + ct can occur with sizable branching ratios ($\sim$10$\sp{-5}-10\sp{-6}$) in a model with three quark-lepton families. Also, the model predicts a branching ratio of $\sim$10$\sp{-4}$ for b $\to$ s$\ell\sp{+}\ell\sp{-}$, which is within the present experimental limit and well above the standard-model prediction of $\sim$10$\sp{-6}$. The process e$\sp{+}$e$\sp{-}$ $\to$ W$\sp{+}$W$\sp{-}$ is studied in the context of the SP(6)$\sb{\rm L}$ $\times$ U(1)$\sb{\rm Y}$ family model. It is found that there are significant deviations in the total cross section $\sigma$(s) and ${\rm d}\sigma\over{\rm dcos\theta}$ from the standard model results due to the existence of an additional neutral gauge boson. We investigate whether the extension of the standard model into the SP(6)$\sb{\rm L}$ $\times$ U(1)$\sb{\rm Y}$ model can significantly change the renormalization group predictions of top quark and higgs masses, under the compositeness condition at some ultraviolet cutoff $\Lambda$. We found, quite surprisingly, that for realistic values of the flavor scale $\Delta$ (10$\sp4$-10$\sp5$ GeV) and for very large $\Lambda$ ($\sbsp{\sim}{>}10\sp{15}$ GeV), the top and higgs masses are lowered only slightly from their standard model values. We present a model where the quark mass hierarchy arises naturally from radiative corrections. The model yields two massless generations at the tree level. They acquire masses from those of the third generation via one loop radiative corrections.

Degree

Ph.D.

Advisors

Kuo, Purdue University.

Subject Area

Particle physics

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