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## GravitinoThe ## Additional recommended knowledgeThe gravitino field is conventionally written as ψ Thus the gravitino is the fermion mediating supergravity interactions, just as the photon is mediating electromagnetism, and the graviton is presumably mediating gravitation. Whenever supersymmetry is broken in supergravity theories, it acquires a mass which is directly the supersymmetry breaking scale. As a proposed solution to the fine tuning problem of the Standard Model, and in order to allow grand unification, the supersymmetry breaking scale needs to be pushed down to the TeV range. Therefore the gravitino mass needs to be of this order, much lower than Planck scale, which is the natural scale for gravity interactions. This difference in energy scales is known as the hierarchy problem. ## Gravitino cosmological problemIf the gravitino indeed has a mass of the order of TeV, then it creates a problem in the standard model of cosmology, at least naively One option is that the gravitino is stable. This would be the case if the gravitino is the lightest supersymmetric particle and R-parity is conserved (or nearly so). In this case the gravitino is a candidate for dark matter, as such gravitini will be created in the very early universe. However, one may calculate the density of gravitini and it turns out to be much higher than the observed dark matter density. The other option is that the gravitino is unstable. Thus the gravitini mentioned above would decay and will not contribute to the observed dark matter density. However, since they decay only through gravitational interactions, their lifetime would be very long, of the order of in natural units, where One possible solution to the cosmological gravitino problem is the split supersymmetry model, where the gravitino mass is much higher than the TeV scale, but other fermionic supersymmetric partners of standard model particles already appear at this scale. ## See also- Supersymmetry
## References**^**T. Moroi, H. Murayama Cosmological constraints on the light stable gravitino Phys.Lett.B303:289-294,1993**^**N. Okada, O. Seto A brane world cosmological solution to the gravitino problem Phys.Rev.D71:023517,2005**^**A. de Gouvea, T. Moroi, H. Murayama Cosmology of Supersymmetric Models with Low-energy Gauge Mediation Phys.Rev.D56:1281-1299,1997**^**M. Endo Moduli Stabilization and Moduli-Induced Gravitino Problem talk given at SUSY’06, 12.Jun.2006]
Categories: Fermions | Hypothetical elementary particles |
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Gravitino". A list of authors is available in Wikipedia. |