SUSY Higgs at the LHC: effects of light charginos and neutralinos

In view of the latest LEP data we consider the effects of charginos and neu tralinos on the two-photon and b (b) over bar signatures of the Higgs at th e LHC. Assuming the usual GUT inspired relation between M-1 and M-2 we show that there are only small regions with moderate tan beta and large stop mi xings that may be dangerous. Pathological models not excluded by LEP which have degeneracy between the sneutrino and the chargino are however a real d anger because of large branching fraction of the Higgs into invisibles. We have also studied models where the gaugino masses are not unified at the GU T scale. We take M-1 = M-2/10 as an example where large reductions in the s ignal at the LHC can occur. However we argue that: such models with a very light neutralino LSP may give a too large relic density unless the sleptons are light. We then combine this cosmological constraint with neutralino pr oduction with light sfermions to further reduce the parameter space that pr ecludes observability of the Higgs at the LHC. We still find regions of par ameter space where the drops in the usual Higgs signals at the LHC can he d rastic. Nonetheless, in such scenarios where Higgs may escape detection we show that one should be able to produce all charginos and neutralinos. Alth ough the heavier of these could cascade into the Higgs, the rates are not t oo high and the Higgs may not always be recovered this way. (C) 2000 Elsevi er Science B.V. All rights reserved.