Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
1998-11-09
Phys.Lett.B452:28-38,1999
Physics
High Energy Physics
High Energy Physics - Phenomenology
9 pages, latex, 7 ps figures
Scientific paper
10.1016/S0370-2693(99)00168-9
We study the extent to which the cosmological fine-tuning problem - why the relic density of neutralino cold dark matter particles $\chi$ is similar to that of baryons - is related to the fine-tuning aspect of the gauge hierarchy problem - how one arranges that M_W << M_P without unnatural choices of MSSM parameters. Working in the minimal supergravity framework with universal soft supersymmetry-breaking parameters as inputs, we find that the hierarchical fine tuning is minimized for \Omega_{\chi} h^2 \sim 0.1. Conversely, imposing \Omega_{\chi} h^2 < 1 does not require small hierarchical fine tuning, but the exceptions to this rule are rather special, with parameters chosen such that m_{\chi}\sim M_Z/2 or M_h/2, or else m_{\chi} \simgt m_t. In the first two cases, neutralino annihilation receives a large contribution from a direct-channel pole, whereas in the third case it is enhanced by the large top Yukawa coupling.
Chankowski Piotr H.
Ellis John
Olive Keith A.
Pokorski Stefan
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