W and Z bosons weak-force boson particle. Thus, this interaction requires a Z boson. These bosons are among the heavyweights of the elementary particles. With masses of and , respectively, the W and Z bosons are almost 80 times as massive as the proton – heavier, even, than entire iron atoms. Their high masses limit the range of the weak interaction. By way of contrast, the photon is the force carrier of the electromagnetic force and has zero mass, consistent with the infinite range of electromagnetism; the hypothetical graviton is also expected to have zero mass. (Although gluons are also presumed to have zero
Technicolor (physics) "M", and the coupling of quarks and leptons to the new particles must be suppressed relative to their coupling to the gauge bosons. This is the case with technicolor, so long as the lightest technivector mesons, "ρ" and "a", are heavier than 200–300 GeV. The "S"-parameter is sensitive to all new physics at the TeV scale, while "T" is a measure of weak-isospin breaking effects. The "U"-parameter is generally not useful; most new-physics theories, including technicolor theories, give negligible contributions to it. The "S" and "T"-parameters are determined by global fit to experimental data including "Z"-pole data from LEP at