Constraint on additional neutral gauge bosons from electroweak radiative corrections

Quantum loop corrections to the quark mixing matrix resulting from additional neutral gauge bosons are computed. Agreement between the finding chemical bondV/sub u//sub d/chemical bond2+chemical bondV/sub u//sub s/chemical bond2+chemical bondV/sub u//sub b/2 = 0.9984 +- 0.0021 and the unitarity value of 1 is used to provide a generic bound on masses and couplings of such bosons. For grand unified models of the type SO(100→SU(3)/sub C/ x SU(2)/sub L/ x U(1)≅U(1)/sub X/, we find m/sub Z//sub >//sub chi//sub =/approx. >266 GeV at 90% confidence limit. That bound also applies to the extra boson in some specific E6 superstring-motivated models. In the general case of E6→SU(3)/sub C/ x SU(2)/sub L/ x U(1) x U(1)/sub eta/ x U(1)/sub eta//sub '/ with m/sub Z//sub >//sub eta//sub '//sub =/≥m/sub Z>//sub eta//sub =/, we obtain the bound m/sub Z//sub >//sub eta//sub '//sub =/≥254 GeV at 90% C.L