Coannihilation Effects in Supergravity and D-Brane Models

Abstract

Coannihilation effects in neutralino relic density calculations are examined for a full range of supersymmetry parameters including large \tan\beta and large A_0 for stau, chargino, stop and sbottom coannihilation with the neutralino. Supergravity models possessing grand unification with universal soft breaking (mSUGRA), models with nonuniversal soft breaking in the Higgs and third generation sparticles, and D-brane models with nonuniversal gaugino masses were analysed. Unlike low \tan\beta where m_0 is generally small, stau coannihilation corridors with high \tan\beta are highly sensitive to A_0, and large A_0 allows m_0 to become as large as 1TeV. Nonuniversal soft breaking models at high \tan\beta also allow the opening of a new annihilation channel through the s-channel Z pole with acceptable relic density, allowing a new wide band in the m_0-m_{1/2} plane with m_{1/2} >~ 400 GeV and $m_0$ rising to 1 TeV. The D-brane models considered possess stau coannihilations regions similar to mSUGRA, as well as small regions of chargino coannihilation. Neutralino-proton cross sections are analysed for all models and it is found that future detectors for halo wimps will be able to scan essentially the full parameter space with m_{1/2} < 1 TeV except for a region with \mu < 0 where accidental cancellations occur when 5 ~<\tan\beta ~< 30. Analytic explanations of much of the above phenomena are given. The above analyses include current LEP bounds on the Higgs mass, large \tan\beta NLO correction to the b \to s \gamma decay, and large \tan\beta SUSY corrections to the b and \tau masses.