A Scenario for Contact Interactions at HERA

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.