A weakly interacting massive particle (WIMP) as the explanation for Dark Matter is very attractive for two reasons. First, its production mechanism is generic and independent from the initial conditions in the history of the universe. The only requirement is that the reheating temperature of the universe should be larger than a few tens of GeV, which is compulsory anyway for baryogenesis.

Second, the existence of WIMPs is directly related to the presence of new particles at the electroweak scale and is easily justified and motivated by the hierarchy problem in the Standard Model (SM). A symmetry is required to guarantee their cosmological stability otherwise they would decay fast into SM particles.

The most studied candidate is the LSP (the lightest supersymmetric particle). In supersymmetry, there is a discrete symmetry called R-parity guaranteeing the stability of the LSP, the neutralino, which acts as a natural dark matter candidate. This scenario has been thoroughly investigated in view of the LHC and gives tight constraints on the minimal supersymmetric standard model.

However, some alternatives to neutralinos and other LSPs do exist, as most of the models introduced to address the naturalness problem turn out to also contain WIMP candidates in their spectrum and therefore naturally provide a solution to the DM puzzle.

For instance, it was shown that in extra dimensional models where the compactification scale is around a TeV, the Kaluza–Klein excitation of the photon is a prototype of WIMP [1, 2, 3]. In some class of flat compactifications, it is stable because of Kaluza-Klein parity, a discrete symmetry of geometrical origin which is a remnant of translational invariance along the extra dimensions.

Second, the existence of WIMPs is directly related to the presence of new particles at the electroweak scale and is easily justified and motivated by the hierarchy problem in the Standard Model (SM). A symmetry is required to guarantee their cosmological stability otherwise they would decay fast into SM particles.

The most studied candidate is the LSP (the lightest supersymmetric particle). In supersymmetry, there is a discrete symmetry called R-parity guaranteeing the stability of the LSP, the neutralino, which acts as a natural dark matter candidate. This scenario has been thoroughly investigated in view of the LHC and gives tight constraints on the minimal supersymmetric standard model.

However, some alternatives to neutralinos and other LSPs do exist, as most of the models introduced to address the naturalness problem turn out to also contain WIMP candidates in their spectrum and therefore naturally provide a solution to the DM puzzle.

For instance, it was shown that in extra dimensional models where the compactification scale is around a TeV, the Kaluza–Klein excitation of the photon is a prototype of WIMP [1, 2, 3]. In some class of flat compactifications, it is stable because of Kaluza-Klein parity, a discrete symmetry of geometrical origin which is a remnant of translational invariance along the extra dimensions.

References:

- [1]^Is the lightest Kaluza-Klein particle a viable dark matter candidate? Geraldine Servant, (Argonne & Chicago U., EFI) , Timothy M.P. Tait, (Argonne) . ANL-HEP-PR-02-032, EFI-02-74, Jun 2002. 30pp.

Published in Nucl.Phys.B650:391-419,2003.

e-Print: hep-ph/0206071 - [2]^Kaluza-Klein dark matter Hsin-Chia Cheng, (Chicago U., EFI) , Jonathan L. Feng H, (UC, Irvine) , Konstantin T. Matchev, (Florida U. & CERN) . EFI-02-95, UCI-TR-2002-23, UFIFT-HEP-02-21, CERN-TH-2002-157, Jul 2002. 4pp.

Published in Phys.Rev.Lett.89:211301,2002.

e-Print: hep-ph/0207125 - [3]^http://www.cambridge.org/catalogue/catalogue.asp?isbn=9780521763684