INTERMEDIATE VECTOR BOSON SELF-ENERGIES FROM A STRONG ELECTROWEAK SECTOR

We calculate the self-energies of the intermediate vector bosons from an effective lagrangian describing possible strongly interacting vector and axial-vector bosons, deduced on the basis of electromagnetic gauge invariance and SU(2) custodial symmetry. Comparison with the standard low-energy parametrization of such self-energies suggests an isospin conserving contribution, called S according to the usual notation, which in principle could also take a negative value, within the permitted range of the model parameters. Technifermion loops in technicolor theories give positive S. Atomic parity experiments indicate a negative central value for S but are affected by large errors and one has to wait for future more accurate determinations.