J. Bernabeu et A. Pilaftsis, CONSTRAINTS FROM LEPTON UNIVERSALITY AT THE Z-PEAK ON UNIFIED THEORIES, Physics letters. Section B, 351(1-3), 1995, pp. 235-241
We suggest the use of a Universality-breaking observable based on lept
on asymmetries as derived from the left-right asymmetry and the tau po
larization at the Z peak, which can efficiently constrain the paramete
r space of unified theories. The new observable is complementary to th
e leptonic partial width differences and it depends critically on the
chirality of a possible non-universal Z-boson coupling to like-flavour
leptons. The LEP/SLC potential of probing universality violation is d
iscussed in representative low-energy extensions of the Standard Model
(SM) that could be derived by supersymmetric grand unified theories,
such as the SM with left-handed and/or right-handed neutral isosinglet
s, the left-right symmetric model, and the minimal supersymmetric SM.