Thursday, October 11, 2012

1210.3019 (Howard Baer et al.)

Post-LHC7 fine-tuning in the mSUGRA/CMSSM model with a 125 GeV Higgs
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Howard Baer, Vernon Barger, Peisi Huang, Dan Mickelson, Azar Mustafayev, Xerxes Tata
The recent discovery of a 125 GeV Higgs-like resonance at LHC, coupled with the lack of evidence for weak scale supersymmetry (SUSY), have severely constrained SUSY models such as mSUGRA/CMSSM. As LHC probes deeper into SUSY model parameter space, the little hierarchy problem -- how to reconcile the Z and Higgs boson mass scale with the scale of SUSY breaking -- will become increasingly exacerbated unless a sparticle signal is found. We evaluate two different measures of fine-tuning in the mSUGRA/CMSSM model. The more stringent of these, \Delta_{HS}, includes effects that arise from the high scale origin of the mSUGRA parameters while the second measure, \Delta_{EW}, is determined only by weak scale parameters: hence, it is universal to any model with the same particle spectrum and couplings. Our results incorporate the latest constraints from LHC7 sparticle searches and require a light Higgs scalar with m_h ~ 123-127 GeV. We present fine-tuning contours in the m_0 vs. m_{1/2} plane for several sets of A_0 and tan\beta values. We also present results for \Delta_{HS} and \Delta_{EW} from a scan over the entire viable model parameter space. We find a \Delta_{HS} > 1000, or at best 0.1% fine-tuning. For the less stringent electroweak fine tuning, we find \Delta_{EW} > 100, or at best 1% fine-tuning. Two benchmark points are presented that have the lowest values of \Delta_{HS} and \Delta_{EW}. Our results provide a quantitative measure for ascertaining whether or not the remaining mSUGRA/CMSSM model parameter space is excessively fine-tuned, and so could provide impetus for considering alternative SUSY models.
View original: http://arxiv.org/abs/1210.3019

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