Coannihilation Effects in Supergravity and D-Brane Models

TL;DR

The paper analyzes coannihilation effects on neutralino relic density in SUSY frameworks spanning universal (mSUGRA), nonuniversal SUGRA, and D-brane models, across a wide range of $\tan\beta$ and $A_0$. It demonstrates that near-degeneracies between the LSP and NLSP (stau, stop, sbottom, or chargino) can create extended coannihilation corridors, with high $\tan\beta$ and nonuniversality enabling a $Z^0$-pole annihilation channel that widens viable regions in the $m_0$–$m_{1/2}$ plane. Direct-detection cross sections $\sigma_{\tilde{\chi}^0_1-p}$ remain largely within reach for $\mu>0$ (typically $>10^{-10}$ pb and often larger), though cancellations for $\mu<0$ can suppress signals. The study integrates LEP Higgs bounds, large $\tan\beta$ corrections to $b\rightarrow s\gamma$ and to fermion masses, providing a comprehensive map of dark matter phenomenology across SUSY-breaking scenarios and guiding experimental sensitivity expectations.

Abstract

Coannihilation effects in neutralino relic density calculations are examined for a full range of supersymmetry parameters including large \tanβand 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 \tanβwhere m_0 is generally small, stau coannihilation corridors with high \tanβare highly sensitive to A_0, and large A_0 allows m_0 to become as large as 1TeV. Nonuniversal soft breaking models at high \tanβalso 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 μ< 0 where accidental cancellations occur when 5 ~<\tanβ~< 30. Analytic explanations of much of the above phenomena are given. The above analyses include current LEP bounds on the Higgs mass, large \tanβNLO correction to the b \to s γdecay, and large \tanβSUSY corrections to the b and τmasses.

Figures (13)

• Figure 1: Allowed corridors in mSUGRA in the $m_0-m_{1/2}$ plane satisfying the relic density constraint for $\mu > 0$, $\tan\beta = 40$ for (from bottom to top) $A_0=m_{1/2}$, 2 $m_{1/2}$, 4$m_{1/2}$. The corridors terminate at low $m_{1/2}$ due to the $b\rightarrow s\gamma$ constraint.
• Figure 2: $(\sigma_{\tilde{\chi}_{1}^{0}-p})_{\rm min}$ in the noncoannilation region as a function of $m_{\tilde{\chi}_{1}^{0}}$ for mSUGRA for $\mu >0$, $\tan\beta = 6$, obtained by varying over the range of $m_0$ and $A_0$.
• Figure 3: $\sigma_{\tilde{\chi}_{1}^{0}-p}$ as a function of $m_{1/2}$ for mSUGRA $\mu >0$, $\tan\beta=40$ and $A_0=2 m_{1/2}$ (upper curve), $4 m_{1/2}$(lower curve).
• Figure 4: $\sigma_{\tilde{\chi}_{1}^{0}-p}$ as a function of $m_{1/2}$ for mSUGRA, $\mu > 0$ for $A_0 = 4\,m_{1/2}$, $\tan\beta = 40$ (upper left curve), $\tan\beta = 3$ (lower left curve).
• Figure 5: $\sigma_{\tilde{\chi}_{1}^{0}-p}$ for mSUGRA for $\mu < 0$, $A_0 = 1500$ GeV, for $\tan\beta = 6$ (short dash), $\tan\beta = 8$ (dotted), $\tan\beta = 10$ (solid), $\tan\beta = 20$ (dot-dash), $\tan\beta=25$ (dashed). Note that the $\tan\beta = 6$ curve terminates at low $m_{1/2}$ due to the Higgs mass constraint, and the other curves terminate at low $m_{1/2}$ due to the $b \rightarrow s\gamma$ constraint.