Asymmetries in t tbar production: LHC versus Tevatron

The measurement of a charge asymmetry in t tbar production at LHC constitutes more than an independent confirmation of the forward-backward asymmetry found at Tevatron. Indeed, both measurements together can be used to identify the source of the asymmetry. This is demonstrated for the case of new Z’, W’ vector bosons and colour-sextet and triplet scalars, exchanged in t, u channels respectively, and a very heavy axigluon in the s channel.