VIRTUAL LSPS AT E(+) E(-) COLLIDERS

Currently popular search strategies for supersymmetric particles may b e significantly affected due to relatively light sneutrinos which deca y dominantly into invisible channels. In certain cases the second ligh test neutralino may also decay invisibly leading to two extra carriers of missing energy (in addition to the lightest supersymmetric particl e (LSP)) - the virtual LSPs (VLSPs). a tree lavel calculation shows th at if the sneutrino mass happens to be in the small but experimentally allowed range (m((v) over bar) approximate to 45-55 GeV), these parti cles together with neutralino pairs may contribute significantly to th e missing energy in the process e(+)e(-) --> gamma + E at LEP-P energi es as an enhancement over the Standard Model or the conventional MSSM predictions. It is further shown that a much larger region of the para meter space can be scanned at a high luminosity e(+)e(-) collider at 5 00 GeV like the proposed NLC machine. Moreover, at both LEP-2 and NLC this process may play a complementary role to direct chargino searches , which may fail due to a near mass degeneracy of the chargino and the sneutrino. Formulae for the cross sections taking into account full m ixings of the charginos and the neutralinos are derived. The signal re mains observable even in the context of more restricted models based o n N=1 SUGRA with common scalar and gaugino masses. A preliminary study of the QED radiative corrections due to soft multiple photon emission as well as hard collinear bremsstrahlung indicates that these correct ions play a crucial role in estimating the background.