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Stop coannihilation in the CMSSM and SubGUT models
Ellis, John,Evans, Jason L.,Luo, Feng,Olive, Keith A.,Zheng, Jiaming Springer Berlin Heidelberg 2018 European Physical Journal C Vol.78 No.5
<P>Stop coannihilation may bring the relic density of heavy supersymmetric dark matter particles into the range allowed by cosmology. The efficiency of this process is enhanced by stop-antistop annihilations into the longitudinal (Goldstone) modes of the <I>W</I> and <I>Z</I> bosons, as well as by Sommerfeld enhancement of stop annihilations and the effects of bound states. Since the couplings of the stops to the Goldstone modes are proportional to the trilinear soft supersymmetry-breaking <I>A</I>-terms, these annihilations are enhanced when the <I>A</I>-terms are large. However, the Higgs mass may be reduced below the measured value if the <I>A</I>-terms are too large. Unfortunately, the interpretation of this constraint on the stop coannihilation strip is clouded by differences between the available Higgs mass calculators. For our study, we use as our default calculator FeynHiggs 2.13.0, the most recent publicly available version of this code. Exploring the CMSSM parameter space, we find that along the stop coannihilation strip the masses of the stops are severely split by the large <I>A</I>-terms. This suppresses the Higgs mass drastically for [FORMULA OMISSION] and [FORMULA OMISSION], whilst the extent of the stop coannihilation strip is limited for [FORMULA OMISSION] and either sign of [FORMULA OMISSION]. However, in sub-GUT models, reduced renormalization-group running mitigates the effect of the large <I>A</I>-terms, allowing larger LSP masses to be consistent with the Higgs mass calculation. We give examples where the dark matter particle mass may reach [FORMULA OMISSION] TeV.</P>
Ellis, John,Evans, Jason L.,Mustafayev, Azar,Nagata, Natsumi,Olive, Keith A. Springer-Verlag 2016 European Physical Journal C Vol.76 No.11
<P>We revisit minimal supersymmetric SU(5) grand unification (GUT) models in which the soft supersymmetry-breaking parameters of the minimal supersymmetric Standard Model (MSSM) are universal at some input scale, M-in, above the supersymmetric gauge-coupling unification scale, M-GUT. As in the constrained MSSM (CMSSM), we assume that the scalar masses and gaugino masses have common values, m(0) and m(1/2), respectively, at Min, as do the tri-linear soft supersymmetry-breaking parameters A(0). Going beyond previous studies of such a super-GUT CMSSM scenario, we explore the constraints imposed by the lower limit on the proton lifetime and the LHC measurement of the Higgs mass, m(h). We find regions of m(0), m(1/2), A(0) and the parameters of the SU(5) superpotential that are compatible with these and other phenomenological constraints such as the density of cold dark matter, which we assume to be provided by the lightest neutralino. Typically, these allowed regions appear for m(0) and m(1/2) in the multi-TeV region, for suitable values of the unknown SU(5) GUT-scale phases and superpotential couplings, and with the ratio of supersymmetric Higgs vacuum expectation values tan beta less than or similar to 6.</P>