Journal
JOURNAL OF HIGH ENERGY PHYSICS
Volume -, Issue 8, Pages -Publisher
SPRINGER
DOI: 10.1007/JHEP08(2012)017
Keywords
Cosmology of Theories beyond the SM; Supersymmetric Standard Model
Categories
Funding
- JSPS [21740160]
- World Premier International Center Initiative (WPI Program), MEXT, Japan
- Ministry of Education, Science, Sports, and Culture (MEXT), Japan [23104008, 23540283]
- [21111006]
- [22244030]
- [21244033]
- Grants-in-Aid for Scientific Research [23540283, 22244030, 21111006] Funding Source: KAKEN
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The recent observations imply that there is an extra relativistic degree of freedom coined dark radiation. We argue that the QCD axion is a plausible candidate for the dark radiation, not only because of its extremely small mass, but also because in the supersymmetric extension of the Peccei-Quinn mechanism the saxion tends to dominate the Universe and decays into axions with a sizable branching fraction. We show that the Higgsino mixing parameter mu is bounded from above when the axions produced at the saxion decays constitute the dark radiation: mu less than or similar to 300 GeV for a saxion lighter than 2m(W), and mu less than the saxion mass otherwise. Interestingly, the Higgsino can be light enough to be within the reach of LHC and/or ILC even when the other superparticles are heavy with mass about 1TeV or higher. We also estimate the abundance of axino produced by the decays of Higgsino and saxion.
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