Light colored scalars from grand unification and the forward-backward asymmetry in t(t)over-bar production

The experimental results on the t (t) over bar production cross section at the Tevatron are well described by the QCD contributions within the standard model, while the recently measured forward-backward asymmetry is larger than predicted within this framework. We consider light colored scalars appearing in a particular SU(5) grand unified theory model within the 45-dimensional Higgs representation. A virtue of the model is that it connects the presence of a light colored SU(2) singlet (Delta(6)) and a color octet weak doublet (Delta(1)) with bounds on the proton lifetime, which constrain the parameter space of both scalars. We find that both the total t (t) over bar production cross section and the forward-backward asymmetry can be accommodated simultaneously within this model. The experimental results prefer a region for the mass of Delta(6) around 400 GeV, while Delta(1) is then constrained to have a mass around the TeV scale as well. We analyze possible experimental signatures and find that Delta(6) associated top production could be probed in the t (t) over bar + jets final states at Tevatron and the LHC.