Forward-Backward t tbar Asymmetry from Anomalous Stop Pair Production

We analyse a simple Standard Model (SM) extension with only two new light fields: a scalar partner of the top (stop) (with mass above m_t) and a light neutral fermion chi^0 (with mass of a few GeV), coupled to SM quarks via a Yukawa interaction. We show that such model can lead to a significant enhancement of the forward-backward asymmetry in t tbar production at the Tevatron via the additional t tbar pairs produced from (stop anti-stop) decays. The model satisfies existing constraints on new-physics searches both at low and high energies, and could even address the cosmological dark-matter abundance. The implications for future searches at the LHC are briefly outlined.