  The experimental results on the t bar t production cross section at the
Tevatron are well described by the QCD contributions within the standard model,
while the recent measurement of the forward-backward asymmetry cannot be
accounted for within this framework. We consider light colored scalars
appearing in a particular SU(5) GUT 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 t bar t 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 bar t + jets final states at
Tevatron and the LHC.

High Energy Physics - Phenomenology