Status of Low Energy Supersymmetry

The most appropriate starting point for reviewing the status of low energy supersymmetry is the status of the Standard Model itself. Its success in describing all the available experimental data becomes more and more pronouced, with all potential deviations disappearing with the increasing precision of data. At present, the Standard Model is successfully tested at 1 permille accuracy up to the LEP2 and TEVATRON energies. One of the most important results following from the precision tests of the Standard Model is the strong indirect indication for a light Higgs boson. Although the sensitivity of electroweak observables to the Higgs boson mass is only logarithmic, the precision of both data and calculations is high enough for obtaining from the fits the upper bound on the Higgs boson mass Mh of about 250 GeV at 95% C.L. The best value of Mh in the fits is in the region of the present direct experimental lower bound, Mh > ∼ 90 GeV. One should stress that these results are obtained strictly in the Standard Model. The best fitted value of Mh can be changed if we admit new physics in the ∆ρ parameter. There is the well known (see, for instance,) “flat direction” in χ, which correlates almost linearly lnMh with (∆ρ) NEW (previously known as lnMh − −mt correlation), as the two effects compensate each other in the electroweak observables like ρ, sinΘeff and MW . In general, however, it is very difficult to find a self-consistent extension of the Standard Model that would use this freedom. b