U(1)A symmetry in two-doublet models, U bosons or light scalars, and psi and Upsilon decays
Abstract
psi and Upsilon decays may be used to search for light neutral spin-1 or spin-0 bosons associated with a broken extra-U(1) symmetry, local or global, acting axially on quarks and leptons, as may be present in supersymmetric theories with a lambda H1 H2 S superpotential term. Recent data on Upsilon --> gamma + invisible neutral constrain an axial, pseudoscalar or scalar coupling to b to fbA < 4 10-7 mU(MeV)/ sqrt Binv, fbP < 4 10-3/ sqrt Binv or fbS < 6 10-3/ sqrt Binv, respectively. This also constrains, from universality properties, couplings to electrons to feA < 4 10-7 mU(MeV)/ sqrt Binv, feP < 4 10-7/ sqrt Binv or feS < 6 10-7/ sqrt Binv. The pseudoscalar a (possibly traded for a light gauge boson, or scalar particle) should then be, for invisible decays of the new boson, for > 96 % singlet and < 4 % doublet, for tan beta > 1. Or, more generally, < 4 % /(tan2 beta Binv) doublet, which implies a very small rate for the corresponding psi decay, B (psi --> gamma + neutral) Binv <~ 10-6/ tan4 beta. Similar results are obtained for new spin-1 or spin-0 neutral bosons decaying into mu+ mu-.