Supersymmetry at the electroweak scale

The simplest interpretation of the global success of the Standard Model is that new physics decouples well above the electroweak scale. Supersymmetric extension of the Standard Model offers the possibility of light chargino and the right-handed stop (with masses below $M_Z$), and still maintaining the successful predictions of the Standard Model. The value of $R_b$ can then be enhanced up to $\sim 0.218$ (the Standard Model value is $\sim 0.216$). Light chargino and stop give important contribution to rare processes such as $b\rightarrow s \gamma$, $\overline K^0-K^0$ and $\overline B^0-B^0$ mixing but consistency with experimental results is maintained in a large region of the parameter space. The exotic four-jet events reported by ALEPH (if confirmed) may constitute a signal for supersymmetry with such a light spectrum and with explicitly broken $R-$parity. Their interpretation as pair production of charginos with $m_C\sim 60$ GeV, with subsequent decay $C\rightarrow \tilde t_R b \rightarrow dsb$ (where $m_{\tilde t}\sim 55$ GeV) leads to signatures very close to the experimental observations.