Relic density of neutralino dark matter in supergravity models

We calculate the relic density (Ω_χ₁⁰h²) of neutralino dark matter in supergravity models with radiative electroweak symmetry breaking, for values of the Higgs sector parameter tanβ≡v₂/v₁ between the two infrared fixed points of the top quark Yukawa coupling, tanβ1.8 and tanβ56. For tanβ10, the CP-odd Higgs pseudoscalar (A⁰) and the heavier CP-even Higgs scalar (H⁰) are much heavier than the lightest neutralino (χ₁⁰), and the annihilation cross section of χ₁⁰ pairs is significantly enhanced only in the vicinity of the lighter CP-even Higgs boson (h⁰) and the Z boson poles. For tanβ40, mA and mH become comparable to 2m_χ₁⁰, and the neutralino annihilation cross section can be significantly enhanced by the poles of the H⁰ and the A⁰ as well. For a cosmologically interesting relic density, 0.1Ω_χ₁⁰h²0.5, 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.