ACCURATE NEUTRALINO RELIC DENSITY COMPUTATIONS IN SUPERGRAVITY MODELS

We investigate the question of the proper thermal averaging of neutral ino annihilation amplitudes which possess poles and thresholds, as the y impact on the calculated neutralino relic density and therefore on t he cosmological viability of supersymmetric models. We focus on two ty pical resonances: namely, the Z boson and the lightest Higgs boson (h) . In the context of supergravity models with radiative electroweak sym metry breaking, an exploration of the whole parameter space of the mod el is possible and the overall relevance of these sophisticated analys es can be ascertained. As an example we choose the minimal SU(5) super gravity model since the presence of such poles is essential to obtain a cosmologically acceptable model. We find that the proper thermal ave raging is important for individual points in parameter space and that the fraction of cosmologically acceptable points is increased somewhat by the accurate procedure. However, qualitatively the new set of poin ts is very similar to that obtained previously using the usual series approximations to the thermal average. We conclude that all phenomenol ogical analyses based on the previously determined cosmologically allo wed set remain valid.