  We use an effective operator framework to study the contributions to the
Tevatron t tbar asymmetry from arbitrary vector bosons and scalars, and compare
with their effect on the t tbar tail at LHC. Our study shows, for example, that
models reproducing the t tbar asymmetry by exchange of Z' and W' bosons or
colour-triplet scalars lead to a large enhancement in the t tbar tail at LHC.
This fact can be used to exclude these models as the sole explanation for the
asymmetry, using the data already collected by CMS and ATLAS. Our analysis is
model independent in the sense that we scan over all possible extra particles
contributing to the asymmetry, and allow for general couplings. We also explore
a class of Standard Model extensions which can accommodate the Tevatron
asymmetry without contributing to the total t tbar cross section at first
order, so that the enhancement of the tail at Tevatron and LHC is moderate.
