The lightest visible-sector supersymmetric particle is likely to be   unstable
  We argue, based on typical properties of known solutions of string/$M$-theory, that the lightest supersymmetric particle of the visible sector will not be stable. In other words, dark matter is {\em not} a particle with Standard Model quantum numbers, such as a WIMP. The argument is simple and based on the typical occurrence of a) hidden sectors, b) interactions between the Standard Model (visible) sector and these hidden sectors, and c) the lack of an argument against massive neutral hidden sector particles being lighter than the lightest visible supersymmetric particle. These conclusions do not rely on arguments such as R-parity violation. 
Bobby S. Acharya, Sebastian A. R. Ellis, Gordon L. Kane, Brent D.   Nelson, Malcolm J. Perry
hep-ph hep-th