https://doi.org/10.1140/epjc/s10052-018-5831-z
Regular Article - Theoretical Physics
Stop coannihilation in the CMSSM and SubGUT models
1
Theoretical Particle Physics and Cosmology Group, Department of Physics, King’s College London, Strand, London, WC2R 2LS, UK
2
National Institute of Chemical Physics and Biophysics, Rävala 10, 10143, Tallinn, Estonia
3
Theoretical Physics Department, CERN, 1211, Geneva 23, Switzerland
4
School of Physics, KIAS, Seoul, 130-722, South Korea
5
Kavli IPMU (WPI) UTIAS, The University of Tokyo, Kashiwa, Chiba, 277-8583, Japan
6
William I. Fine Theoretical Physics Institute, School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, 55455, USA
7
Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan
* e-mail: jlevans@kias.re.kr
Received:
15
February
2018
Accepted:
21
April
2018
Published online:
28
May
2018
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 W and Z 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 A-terms, these annihilations are enhanced when the A-terms are large. However, the Higgs mass may be reduced below the measured value if the A-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 A-terms. This suppresses the Higgs mass drastically for 
and 
, whilst the extent of the stop coannihilation strip is limited for 
and either sign of . However, in sub-GUT models, reduced renormalization-group running mitigates the effect of the large A-terms, allowing larger LSP masses to be consistent with the Higgs mass calculation. We give examples where the dark matter particle mass may reach 
TeV.
© The Author(s), 2018
