Inparticle physics, the lightest supersymmetric particle (LSP) is the generic name given to the lightest of the additional hypothetical particles found in supersymmetric models. In models with R-parity conservation, the LSP is stable; in other words, it cannot decay into any Standard Model particle, since all SM particles have the opposite R-parity. There is extensive observational evidence for an additional component of the matter density in the universe, which goes under the name dark matter. The LSP of supersymmetric models is a dark matter candidate and is a weakly interacting massive particle (WIMP).[1]
The LSP is unlikely to be a charged wino, charged higgsino, slepton, sneutrino, gluino, squark, or gravitino but is most likely a mixture of neutral higgsinos, the bino and the neutral winos,[2] i.e. a neutralino. In particular, if the LSP were charged (and is abundant in our galaxy) such particles would have been captured by the Earth's magnetic field and form heavy hydrogen-like atoms.[3] Searches for anomalous hydrogen in natural water[4] however have been without any evidence for such particles and thus put severe constraints on the existence of a charged LSP.
Dark matter particles must be electrically neutral; otherwise they would scatter light and thus not be "dark". They must also almost certainly be non-colored.[5] With these constraints, the LSP could be the lightest neutralino, the gravitino, or the lightest sneutrino.
Inextra-dimensional theories, there are analogous particles called LKPs or Lightest Kaluza–Klein Particle. These are the stable particles of extra-dimensional theories.[7]
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Potential dark galaxies |
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