We study the extent to which the cosmological fine-tuning problem - why the relic density of neutralino cold dark matter particles χ is similar to that of baryons - is related to the fine-tuning aspect of the gauge hierarchy problem - how one arranges that MW ≪ MP 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 Ωχh2 ∼ 0.1. Conversely, imposing Ωχh2 < 1 does not require small hierarchical fine tuning, but the exceptions to this rule are rather special, with parameters chosen such that mχ ∼ MZ/2 or Mh/2, or else mχ ≳ mt. 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.
|Original language||English (US)|
|Number of pages||11|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - 1999|
Bibliographical noteFunding Information:
We thank Marek Olechowski for collaboration at the early stage of this project. We would also like to thank Toby Falk for many helpful conversations. The work of P.H.Ch. and S.P. has been partly supported by the Polish State Committee for Scientific Research grant 2 P03B 040 12 (1998–1999). The work of K.A.O. was supported in part by DOE grant DE–FG02–94ER–40823 at the University of Minnesota.