Astronomers have known there was something missing from universe for years, Zwicky first calculated how stars should move under gravity in a galaxy back in 1933, and found there was far more matter in a galaxy than could be accounted for by stars. But it wasn't until the 1990s that astronomers really begin to believe in dark matter. But now finally experiments are starting to get close to discovering what it all the mysterious missing matter really is. And looking more and more like it isn't a LSP.
The LSP, lightest super-symmetric particle, is super-symmetries candidate for a dark matter particle. Its stable, once super-symmetrics has a new symmetry, R-parity, add to it, in an Ad-hoc ways. Its dark, provide a non-charge particle, happens to be the lightest, and its made in the right ammount, once super-symmetry is ad-hoc turned to the right masses. The LSP has been
physicists first guess at what dark matter is for some twenty years. Many due, to physicists love
of syper-symmetry and super string theory. See Peter Woit's not even wrong for a criticism (or demolition) of Super-String theory
What the LSP isn't, is seen. Perphaps this is not surprising for a dark particle, but evidence for of dark matter is starting to arrive. The DAMA experiment, found evidence of Dark Matter in thermal motion through the solar system at 8 sigma levels (5 sigma is a good detection level, 8 is much better). All the other dark matter detect should nothing. The LSP just wouldn't fit
the combination of seen at DAMA and not elsewhere.
The LSP is supposedly majorana particle, it is its own anti-particle. This means that two LSP's would annihilate if brought together, producing high energy normal particles doing so. This was fine in the very early universe, it helped remove enough of the them to get, the amount of LSP that exist turned, to the 20% of the universe, we need for dark matter. But, in the modern universe, where-ever dark matter clumps together they should be signals of this annihilation, in particular there should be anti-protons at high energies. These just haven't been seen, despite evidence for high energy positrons at high energies in cosmic rays. Phenomenologist's started talking about leptophilic or hadrophobic LSPs, inventing new theory turning the LSP in something that doesn't annihilate into anti-protons.
LSP annihilation also means that dense enough clump would start shining, forming so called dark stars in the early universe, these stars are actually bright and super-massive, and again so far not seen. When they run out of the dark matter to annihilate they would clasps straight to blacks holes, froming immediately sized black holes, in the modern universe, which again aren't seen.
These combination of three non-observations of LSPs is starting to look very bad for both, the LSP as a dark matter candidate, and for super-symmetry as a theory. If the LHC now happily running with its 3.5 TeV Beams for the next two years, finds no signal of LSPs things will start to look very dark for the LSP.