Explaining the ttbar Forward-Backward Asymmetry from a GUT-Inspired Model

Abstract

We consider a model that includes light colored scalars from the {\bf 45} and {\bf 50} representations of SU(5) in order to explain the CDF- and D$\text{O}$-reported $t\bar{t}$ forward-backward asymmetry, $A_{FB}^{t\bar{t}}$. These light scalars are, labeled by their charges under the Standard Model gauge groups, the $(6,1{)}_{4/3}$ and $(\bar{6},3{)}_{1/3}$ from the {\bf 50} and the $(8,2{)}_{1/2}$ from the {\bf 45}. When the Yukawa coupling of the {\bf 50} is reasonably chosen and that of the {\bf 45} kept negligible at the scale of $M_Z$, the model yields phenomenologically viable results in agreement with the total $A_{FB}^{t\bar{t}}$ reported by CDF at the 0.7$\sigma$ level and with $A_{FB}^{t\bar{t}}(M_{t\bar{t}}\ge 450\text{GeV})$ at the 2.2$\sigma$ level. Additionally, the Yukawa coupling of the {\bf 50} remains perturbative to the GUT scale (which defines a "reasonably chosen" value at $M_Z$), and the presence of the light scalar from the {\bf 45} allows for gauge coupling unification at a scale of $M_{GUT}\sim 10^{17}$ GeV.

Comments: 18 pages, 3 figures, 2 tables, 1 appendix, typos corrected, reference added, published on JHEP