Non-Baryonic Dark Matter -- A Theoretical Perspective

I review axions, neutralinos, axinos, gravitinos and super-massive Wimpzillas as dark matter candidates.Comment: Invited review talk at COSMO-98, the Second International Workshop on Particle Physics and the Early Universe, Asilomar, USA, November 15-20, 199

Axino - New Candidate for Cold Dark Matter

Supersymmetric extensions of the Standard Model when combined with the Peccei-Quinn solution to the strong CP problem necessarily contain also the axino, the fermionic partner of the axion. In contrast to the neutralino and the gravitino, the axino mass is generically not of the order of the supersymmetry breaking scale and can be much smaller. The axino is therefore an intriguing candidate for a stable superpartner. The axinos are a natural candidate for cold dark matter in the Universe when they are generated non-thermally through out-of-equilibrium neutralino decays or via a competing thermal production mechanism through scatterings and decays of particles in the plasma. We identify axino masses in the range of tens of MeV to several GeV (depending on the scenario) as corresponding to cold axino relics if the reheating temperature T_R is less than about 5 \times 10^4 GeV. At higher T_R and lower mass, axinos could constitute warm dark matter. In the scenario with axinos as stable relics the gravitino problem finds a natural solution. The lightest superpartner of the Standard Model spectrum will remain stable in high-energy detectors but may be either neutral or charged. The usual constraint Omega*h^2<1 on the relic abundance of the lightest neutralino does not hold.Comment: Based on invited plenary talks at the 4th International Workshop on Particle Physics and the Early Universe (COSMO-2000), Cheju, Cheju Island, Korea, September 4-8, 2000 and the 3rd International Workshop on the Identification of Dark Matter (IDM-2000), York, England, 18-22 September 200

Non-Baryonic Dark Matter

There exist several well-motivated candidates for non-baryonic cold dark matter, including neutralinos, axions, axinos, gravitinos, Wimpzillas. I review the dark matter properties of the neutralino and the current status of its detection. I also discuss the axino as a new interesting alternative.Comment: Invited plenary review talk given at 6th International Workshop on Topics in Astroparticle and Underground Physics (TAUP 99), 6-10 September, 1999, Paris, Franc