Gravitino
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The gravitino is the supersymmetric partner of the graviton, as predicted by theories combining general relativity and supersymmetry, i.e. supergravity theories. If it exists it is a fermion of spin 3/2, therefore obeys Rarita-Schwinger equation.
The gravitino can be seen as the fermion mediating supergravity interactions. Whenever supersymmetry is broken in supergravity theories, it acquires a mass which is directly the supersymmetry breaking scale.
Because of the hierarchy problem of the Standard Model, the supersymmetry breaking scale (as well as any new physics scale) needs to be pushed down to the TeV range. The main difficulty is therefore to provide a small (compared to the Planck scale, which is the natural scale for gravity interactions) gravitino mass.
[edit] Light Gravitino
If the gravitino is the lightest supersymmetric particle and R-parity is conserved (or nearly so), many or all supersymmetric particles can decay into their superpartner and a gravitino which yields the following effects:
1) The gravitino could make up most of the dark matter in the universe.
2) The decays might be detected at future particle accelerators. This can be done if either a neutral supersymmetric particle decays within the detector (only for very short lifetimes) or if a charged supersymmetric particle is stopped outside the detector (possible for longer lifetimes, too).
However, this is not strongly believed. The leading candidate for the lightest supersymmetric particle is the neutralino.
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| Fermions: Quarks: (Up · Down · Strange · Charm · Bottom · Top) | Leptons: (Electron · Muon · Tau · Neutrinos) | |
| Gauge bosons: Photon | W and Z bosons | Gluons | |
| Not yet observed: Higgs boson | Graviton | Other hypothetical particles | |
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