MFV reductions of MSSM parameter space
S.S. AbdusSalam
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C.P. Burgess
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F. Quevedo
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P.le A. Moro
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I-
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Roma
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Italia
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Hamilton ON
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Canada
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Cambridge
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U.K.
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DAMTP, Cambridge University
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CH-1211
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Gen`eve 23
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Suisse
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Waterloo
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Canada
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Perimeter Institute for Theoretical Physics
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Division PH -TH
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CERN
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The Abdus Salam ICTP
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Department of Physics & Astronomy, McMaster University
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INFN - Sezione di Roma
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Open Access
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c The Authors
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[54] M.W. Cahill-Rowley
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J.L. Hewett, A. Ismail and T.G. Rizzo, More energy, more searches
The 100+ free parameters of the minimal supersymmetric standard model (MSSM) make it computationally difficult to compare systematically with data, motivating the study of specific parameter reductions such as the cMSSM and pMSSM. Here we instead study the reductions of parameter space implied by using minimal flavour violation (MFV) to organise the R-parity conserving MSSM, with a view towards systematically building in constraints on flavour-violating physics. Within this framework the space of parameters is reduced by expanding soft supersymmetry-breaking terms in powers of the Cabibbo angle, leading to a 24-, 30- or 42-parameter framework (which we call MSSM-24, MSSM-30, and MSSM-42 respectively), depending on the order kept in the expansion. We provide a Bayesian global fit to data of the MSSM-30 parameter set to show that this is manageable with current tools. We compare the MFV reductions to the 19-parameter pMSSM choice and show that the pMSSM is not contained as a subset. The MSSM-30 analysis favours a relatively lighter TeV-scale pseudoscalar Higgs boson and tan 10 with multi-TeV sparticles.
1 Introduction The models 2 3
Expansions in small mixing angles
The MSSM-30 fit
Conclusions and outlook
(on the cover of The Hitchhikers Guide to the Galaxy [1])
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Supersymmetry, when linearly realised, requires the existence of superpartners to the
known elementary particles, and robustly dictates their quantum numbers. Less robustly
dictated are their masses and couplings once supersymmetry is spontaneously broken, as
experiments demand it must be. A full description of these requires the more than 100
parameters of the supersymmetry-breaking sector of the R-parity conserving minimal
supersymmetric Standard Model (MSSM).
The challenge of confronting such a vast parameter space with data drives the
development of various kinds of well-motivated benchmark models. The earliest of these, the
cMSSM/mSUGRA [24], specialises to a restricted parameter space motivated by what
would be generated if supersymmetry were broken in a flavour-blind hidden sector (as
suggested by the earliest gravity-mediation models). This simple model is one of the main
benchmarks against which LHC results are compared, with the result that it is in real
tension with the data.
But should this tension be regarded as evidence against supersymmetry, even if only
in its linearly realised1 form? Answering this requires a more detailed exploration of the
parameter space, yet a complete scan of the total parameters still remains beyond our
current computational capabilities.
What is needed is a more strategic survey of the possibilities, of which several
approaches have emerged. One approach for example, Gauge-Mediated Supersymmetry
1See [5] for a well-motivated example where supersymmetry breaks at the electroweak scale but is
nonlinearly realised in the Standard Model sector, and so doesnt require the existence of MSSM superpartners
like squarks and sleptons.
Breaking (GMSB) [6], or more sophisticated string-motivated gravity mediation
mechanisms [7] is to explore alternative mechanisms of supersymmetry breaking whose
low-energy implications differ from those of the minimal gravity-mediated picture.
Another focusses less on surveying the parameter space and more on the generic features
of the underlying production and decay mechanisms, such as appear in simplified
models [8]. Comparison of such models to the data can quantify which of these mechanisms
are favoured or disfavoured. A more specific simplified models approach instead focuses
on those interactions that take part in the naturalness issues that underlie the motivation
for supersymmetry in the first place [911].
A third approach is to try to broadly survey the allowed parameter space, but to use
prior knowledge about other constraints (like limits on flavour and CP violations) to cut
down the range of parameters examined at the LHC. Of course this would be simple if it
were just a matter of removing couplings that are excluded by other constraints. How the
parameters are best pruned is more of a judgement call when the couplings of interest are
not directly forbidden by other observations.
The phenomenological MSSM (pMSSM) [12] is one of the leading approaches along
these lines which stakes out a 19-parameter subset of MSSM by removing all members
of potentially dangerous families (...truncated)