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$\O$-reported $t\bar{ t}$ forward-backward asymmetry, $A^{ t\bar{ t}}_{ FB}$. 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 $A^{ t\bar{ t}}_{ FB}$ reported by CDF at the 0.7$\sigma$ level and with $A^{ t\bar{ t}}_{ FB} (M_{ t\bar{ t}} \ge 450 \text{ GeV})$ 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.
Categories: hep-ph