  We perform a comprehensive study of the allowed range for the Tevatron t tbar
forward-backward asymmetries in six representative new physics models: a
flavour-changing Z' boson, a scalar isodoublet, a W' boson, a heavy axigluon, a
colour-triplet and a colour-sextet scalar. We devote special attention to the
constraints from the t tbar tail at LHC on the parameter space, which will be
dramatic if the measurements agree with the SM prediction, specially for Z' and
W' bosons. We also study the predictions for the charge asymmetries at LHC and
compare several proposed definitions.
