  The four fermion contact interactions, required to explain the anomalous HERA
result, could come from the exchange of new heavy (probably composite)
resonances. Depending on their charges and quantum numbers, one gets different
scenarios and finds that many of these configurations are unsuitable. For
example, new neutral resonances seems to be disfavored by the data coming from
the TEVATRON, LEP 2 and atomic parity violation. These experiments allow only
few helicity combinations that cannot arise from neutral currents in a natural
way. On the contrary, a global large symmetry SU(8) * SU(8) (which is contained
in SU(16)) embeds some lepto-quarks of spin 1 that could give suitable four
fermion interactions (compatible with all other experiments) if these
resonances are the lightest new (probably composite) states with a mass
comparable to the scale of the contact interactions.
