EXTRA U(1)S AND NEW FORCES

We discuss possible extra U(1) gauge symmetries for extensions of the standard model, in connection with their Higgs boson sectors. The more electroweak Higgs doublets, the larger the number of extra U(1) symmetries which may be gauged. For small numbers of Higgs doublets such extra U(1) symmetries usually appear as blind to quark flavor, while this is not necessary for leptons. With only one Higgs doublet any extra U(1) generator must act on quarks and leptons as a linear combination of the baryonic and leptonic numbers B and Li with the weak hypercharge Y. With two or more Higgs doublets they may act as linear combinations of B, Li and Y with axial baryonic and/or leptonic symmetry generators. We also discuss extra U(1) groups in left-right symmetric and grand-unified theories. The corresponding neutral gauge bosons, U, in general mix with the Z bosons, and may be heavy, light, or even remain massless. The strength of the resulting interaction, of unknown range λU = h {combining short stroke overlay}/mUc, is proportional to 1/λU2, and also depends on the extra U(1) symmetry-breaking scale. For very light U bosons this interaction may appear as a deviation from the laws of gravitation (or electromagnetism). After mixing with the Z current the new current is then purely vectorial, in the case of a single Higgs doublet; or it also includes an axial part, which could be responsible for the direct production of U bosons in particle physics experiments, as well as for a new spin-spin force. The vector part of the current is associated with the fifth force charge Q5 = xB + yiLi + zQ, or, in the framework of grand-unified theories: Q5 = x(B - L) + zQ. We discuss, finally, some of the main physical implications of this analysis. © 1990.