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Nonexotic neutral gauge bosons

2003; American Physical Society; Volume: 68; Issue: 3 Linguagem: Inglês

10.1103/physrevd.68.035012

1538-4500

Thomas Appelquist, Bogdan A. Dobrescu, Adam R. Hopper,

Cosmology and Gravitation Theories

We study theoretical and experimental constraints on electroweak theories including a new color-singlet and electrically neutral gauge boson. We first note that the electric charges of the observed fermions imply that any such ${Z}^{\ensuremath{'}}$ boson may be described by a gauge theory in which the Abelian gauge groups are the usual hypercharge along with another $U(1)$ component in a kinetic-diagonal basis. Assuming that the observed quarks and leptons have generation-independent $U(1)$ charges, and that no new fermions couple to the standard model gauge bosons, we find that their $U(1)$ charges form a two-parameter family consistent with anomaly cancellation and viable fermion masses, provided there are at least three right-handed neutrinos. We then derive bounds on the ${Z}^{\ensuremath{'}}$ mass and couplings imposed by direct production and Z-pole measurements. For generic charge assignments and a gauge coupling of electromagnetic strength, the strongest lower bound on the ${Z}^{\ensuremath{'}}$ mass comes from Z-pole measurements, and is of the order of 1 TeV. If the new $U(1)$ charges are proportional to $B\ensuremath{-}L,$ however, there is no tree-level mixing between the Z and ${Z}^{\ensuremath{'}},$ and the best bounds come from the absence of direct production at CERN LEP II and the Fermilab Tevatron. If the $U(1)$ gauge coupling is one or two orders of magnitude below the electromagnetic one, these bounds are satisfied for most values of the ${Z}^{\ensuremath{'}}$ mass.