Limits on Associated Production of Visibly and Invisibly Decaying Higgs   Bosons from Z Decays
  Many extensions of the standard electroweak model Higgs sector suggest that the main Higgs decay channel is "invisible", for example, $h \to J J$ where $J$ denotes the majoron, a weakly interacting pseudoscalar Goldstone boson associated to the spontaneous violation of lepton number. In many of these models the Higgs boson may also be produced in association to a massive pseudoscalar boson (HA), in addition to the standard Bjorken mechanism (HZ). We describe a general strategy to determine limits from LEP data on the masses and couplings of such Higgs bosons, using the existing data on acoplanar dijet events as well as data on four and six $b$ jet event topologies. For the sake of illustration, we present constraints that can be obtained for the ALEPH data. 
F. De Campos, M. A. Garcia-Jare\~NO, Anjan S. Joshipura, J. Rosiek, J.   W. F. Valle and D. P. Roy