Updated Post-WMAP Benchmarks for Supersymmetry

TL;DR

The paper updates CMSSM benchmark points in light of the WMAP-derived relic-density window for cold dark matter, introducing WMAP lines that link m1/2 and m0 across tanβ and μ signs. It analyzes how small or substantial shifts in SUSY-breaking parameters place the benchmarks on these lines, evaluates the resulting sparticle spectra and decay patterns, and assesses the discovery reach of the LHC and future e+e− colliders (including CLIC) along these lines. It highlights the complementarity of hadron and lepton colliders for probing the neutralino sector and demonstrates that collider data could, in principle, enable predictions of the dark matter relic density, albeit with caveats in tricky regions like funnels and focus-point. Overall, the work provides a practical framework for testing CMSSM dark-matter hypotheses with current cosmological constraints and next-generation collider capabilities, while emphasizing the importance of cross-checks among different experimental modalities.

Abstract

We update a previously-proposed set of supersymmetric benchmark scenarios, taking into account the precise constraints on the cold dark matter density obtained by combining WMAP and other cosmological data, as well as the LEP and b -> s gamma constraints. We assume that R parity is conserved and work within the constrained MSSM (CMSSM) with universal soft supersymmetry-breaking scalar and gaugino masses m_0 and m_1/2. In most cases, the relic density calculated for the previous benchmarks may be brought within the WMAP range by reducing slightly m_0, but in two cases more substantial changes in m_0 and m_1/2 are made. Since the WMAP constraint reduces the effective dimensionality of the CMSSM parameter space, one may study phenomenology along `WMAP lines' in the (m_1/2, m_0) plane that have acceptable amounts of dark matter. We discuss the production, decays and detectability of sparticles along these lines, at the LHC and at linear e+ e- colliders in the sub- and multi-TeV ranges, stressing the complementarity of hadron and lepton colliders, and with particular emphasis on the neutralino sector. Finally, we preview the accuracy with which one might be able to predict the density of supersymmetric cold dark matter using collider measurements.

Figures (13)

• Figure 1: The shaded strips display the regions of the $(m_{1/2}, m_0)$ plane that are compatible EOSS with $0.094 < \Omega_\chi h^2 < 0.129$ in the 'bulk', coannihilation 'tail', and rapid-annihilation 'funnel' regions, as well as the laboratory constraints, for (a) $\mu > 0$ and $\tan \beta = 5, 10, 20, 35$ and 50, and (b) for $\mu < 0$ and $\tan \beta = 10$ and 35. The parts of these 'WMAP lines' for $\mu > 0$ compatible with $g_\mu - 2$ at the 2-$\sigma$ level have lighter (pink) shading g-2. The updated post-WMAP benchmark scenarios are marked in red. Points (E',F') in the focus-point region have larger values of $m_0$.
• Figure 2: Comparison of the mass differences $\Delta M \equiv |m_{\tilde{\tau}_1} - m_\chi|$ along the WMAP lines, as calculated in the SSARD code (dots) and ISASUGRA 7.67 using the same values of $m_0$ (dashed lines), as functions of $m_{1/2}$ for $\mu > 0$ and $\tan \beta = 5, 10, 20, 35, 50$ and $\mu < 0, \tan \beta = 10$. We see the need to shift $m_0$ systematically, particularly at larger $m_{1/2}$ and $\tan \beta$. This has been done for the solid lines, which are improved ISASUGRA 7.67 fits to the WMAP lines described in the text.
• Figure 3: Summary of the numbers of MSSM particles that may be detectable at various accelerators in the updated benchmark scenarios. As in Bench, we see that the capabilities of the LHC and of linear $e^+ e^-$ colliders are largely complementary. We re-emphasize that mass and coupling measurements at $e^+ e^-$ colliders are usually much cleaner and more precise than at hadron-hadron colliders such as the LHC, where, for example, it is not known how to distinguish the light squark flavours.
• Figure 4: Dominant branching ratios of the next-to-lightest neutralino $\chi_2$ as functions of $m_{1/2}$ along the WMAP lines for (a) $\tan \beta = 5$, (b) $\tan \beta = 10$, (c) $\tan \beta = 20$, (d) $\tan \beta = 35$ and (e) $\tan \beta = 50$, all for $\mu > 0$, and (f) $\tan \beta = 10$ for $\mu < 0$. The locations of updated benchmark points along these WMAP lines are indicated, as are the upper limits on $m_{1/2}$ in panels (a, b, c) and (f).
• Figure 5: Supersymmetric event signatures at the LHC: the numbers of $Z$ bosons (upper left), light Higgs bosons $h$ (upper right), $\tau$ leptons (lower left) and three-lepton final states per supersymmetric event are shown as functions of $m_{1/2}$ along the WMAP lines for four values of $\tan \beta$, all with $\mu > 0$. These plots were obtained with PYTHIA 6.215PYTHIA interfaced to ISASUGRA 7.67ISASUGRA.