We calculate the relic density $\left({\Omega }_{{\chi }_1^0}{h}^2\right)$ of neutralino dark matter in supergravity models with radiative electroweak symmetry breaking, for values of the Higgs sector parameter $\tan \beta \equiv v_2{/v}_1$ between the two infrared fixed points of the top quark Yukawa coupling, $\tan \beta \simeq 1.8$ and $\tan \beta \simeq 56$. For $\tan \beta \lesssim 10$, the $\mathrm{CP}$-odd Higgs pseudoscalar ${(A}^0)$ and the heavier $\mathrm{CP}$-even Higgs scalar ${(H}^0)$ are much heavier than the lightest neutralino $\left({\chi }_1^0\right)$, and the annihilation cross section of ${\chi }_1^0$ pairs is significantly enhanced only in the vicinity of the lighter $\mathrm{CP}$-even Higgs boson ${(h}^0)$ and the $Z$ boson poles. For $\tan \beta \gtrsim 40$, $m_A$ and $m_H$ become comparable to ${2m}_{{\chi }_1^0}$, and the neutralino annihilation cross section can be significantly enhanced by the poles of the $H^0$ and the $A^0$ as well. For a cosmologically interesting relic density, $0.1\lesssim {\Omega }_{{\chi }_1^0}{h}^2\lesssim 0.5$, we find that the supergravity parameter space is tightly constrained. The mass spectra for supersymmetric particles are presented for unification mass parameters in the cosmologically interesting region.

• Received 24 April 1997

DOI:https://doi.org/10.1103/PhysRevD.57.3131