BOUNDING EFFECTIVE OPERATORS AT THE ONE-LOOP LEVEL - THE CASE OF 4-FERMION NEUTRINO INTERACTIONS

The contributions of non-standard four-neutrino contact interactions to electroweak observables are considered at the one-loop level by using the effective quantum field theory language. The analysis is done in terms of three unknown parameters: the strength of the non-standard neutrino interactions, (F) over tilde, an additional derivative coupling needed to renormalize the divergent contributions that appear when the four-neutrino interactions are used at the loop level and a non-standard non-derivative Z-(v) over bar v coupling. Then, the precise measurements of the invisible width of the Z-boson at LEP and the data on the neutrino deep-inelastic scattering yield the result (F) over tilde = (-100+/-140)G(F). Assuming that there are no unnatural cancellations between the contributions of the three effective couplings a much stronger bound is obtained: \(F) over tilde\ less than or similar to 2G(F), which is a factor 200 better than the one obtained in previous analyses based on tree level calculations.