Coannihilation effects in supergravity and D-brane models

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 mo is generally small, stau coannihilation corridors with high tan are highly sensitive to A(0), and large A(0) allows m(0) to become as large as 1 TeV. 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 to m(1/2) greater than or similar to 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 in m(1/2) < 1 TeV except for a region with mu < 0 where accidental cancellations occur when 5 less than or similar to tan less than or similar to 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 --> s gamma decay, and large tan beta SUSY corrections to the b and tau masses. (C) 2001 Elsevier Science B.V All rights reserved.