Supersymmetric Dark Matter Candidates

TL;DR

Ellis and Olive examine supersymmetric extensions of the Standard Model with a focus on dark matter candidates under $R$-parity conservation. They compare neutralino and gravitino LSP scenarios, and analyze how renormalization-group evolution and electroweak symmetry breaking shape the low-energy spectrum, while exploring CMSSM and mSUGRA parameter spaces along with non-universal Higgs masses and lower-scale boundary conditions. The work discusses cosmological and astrophysical constraints, especially from Big-Bang Nucleosynthesis and relic-density measurements, and outlines collider signatures and detection prospects relevant to distinguishing these scenarios. It highlights how current observations constrain viable SUSY parameter regions and how forthcoming collider data can reveal which dark-matter candidate, if any, is realized in Nature.

Abstract

After reviewing the theoretical, phenomenological and experimental motivations for supersymmetric extensions of the Standard Model, we recall that supersymmetric relics from the Big Bang are expected in models that conserve R parity. We then discuss possible supersymmetric dark matter candidates, focusing on the lightest neutralino and the gravitino. In the latter case, the next-to-lightest supersymmetric particle is expected to be long-lived, and possible candidates include spartners of the tau lepton, top quark and neutrino. We then discuss the roles of the renormalization-group equations and electroweak symmetry breaking in delimiting the supersymmetric parameter space. We discuss in particular the constrained minimal extension of the Standard Model (CMSSM), in which the supersymmetry-breaking parameters are assumed to be universal at the grand unification scale, presenting predictions from a frequentist analysis of its parameter space. We also discuss astrophysical and cosmological constraints on gravitino dark matter models, as well as the parameter space of minimal supergravity (mSUGRA) models in which there are extra relations between the trilinear and bilinear supersymmetry-breaking parameters, and between the gravitino and scalar masses. Finally, we discuss models with non-universal supersymmetry-breaking contributions to Higgs masses, and models in which the supersymmetry-breaking parameters are universal at some scale below that of grand unification. http://cambridge.org/us/catalogue/catalogue.asp?isbn=9780521763684

Figures (7)

• Figure 1: The renormalization-group evolution of the mass parameters in the CMSSM, assuming $m_{1/2} = 250$ GeV, $m_0 = 100$ GeV, $\tan \beta = 3$, $A_0 = 0$, and $\mu < 0$. We thank Toby Falk for providing this figure.
• Figure 2: The $(m_{1/2}, m_0)$ planes for (a) $\tan \beta = 10$ and (b) $\tan \beta = 50$, assuming $\mu > 0$, $A_0 = 0$, $m_t = 175$ GeV and $m_b(m_b)^{\overline {MS}}_{SM} = 4.25$ GeV. The near-vertical (red) dot-dashed lines are the contours for $m_h = 114$ GeV, and the near-vertical (black) dashed line is the contour $m_{\chi^\pm} = 104$ GeV. Also shown by the dot-dashed curve in the lower left is the region excluded by the LEP bound $m_{\tilde{e}} > 99$ GeV. The medium (dark green) shaded region is excluded by $b \to s \gamma$, and the light (turquoise) shaded area is the cosmologically preferred region. In the dark (brick red) shaded region, the LSP is the charged ${\tilde{\tau}}_1$. The region allowed by the E821 measurement of $a_\mu$ at the 2-$\sigma$ level, is shaded (pink) and bounded by solid black lines, with dashed lines indicating the 1-$\sigma$ ranges.
• Figure 3: The $(m_0, m_{1/2})$ plane in the CMSSM showing the regions favoured in a likelihood analysis at the 68% (blue) and 95% (red) confidence levels Buchmueller:2008qe. The best-fit point is shown as the black point. Also shown are the discovery contours in different channels for the LHC with 1/fb (2/fb for the Higgs search in cascade decays of sparticles) ATLAS:1999frBall:2007zza.
• Figure 4: The $(m_{1/2}, m_0)$ planes for $m_t = 172.7$ GeV, $A_0=0$, $\mu > 0$ and $\tan \beta = 10$ with $m_{3/2} = 0.2 m_0$ without (a) and with (b) the effects of metastable stau bound states included. The regions to the left of the solid black lines are not considered, since there the gravitino is not the LSP. In the orange (light) shaded regions, the differences between the calculated and observed light-element abundances are no greater than in standard BBN without late particle decays. In the pink (dark) shaded region in panel (b), the abundances lie within the ranges favoured by observation. The significances of the other lines and contours are explained in the text.
• Figure 5: Examples of mSUGRA $(m_{1/2}, m_0)$ planes with contours of $\tan \beta$ superposed, for $\mu > 0$ and (a) the simplest Polonyi model with $A_0/m_0 = 3 - \sqrt{3}$, and (b) $A_0/m_0 = 2.0$, all with $B_0 = A_0 -m_0$. In each panel, we show the regions excluded by the LEP lower limits on MSSM particles and those ruled out by $b \to s \gamma$ decay (medium green shading): the regions favoured by $g_\mu - 2$ are very light (yellow) shaded, bordered by a thin (black) line. The dark (chocolate) solid lines separate the neutralino and gravitino LSP regions. The regions favoured by WMAP in the neutralino LSP case have light (turquoise) shading. The dashed (pink) line corresponds to the maximum relic density for the gravitino LSP, and regions allowed by BBN constraint neglecting the effects of bound states on NSP decay are light (yellow) shaded.