Next-to-minimal supersymmetric model close to the R-symmetry limit and naturalness in h-->aa decays for m_a<2m_b

Dominant decay of a SM-like Higgs boson into particles beyond those contained in the minimal supersymmetric standard model has been identified as a natural scenario to avoid fine-tuning in electroweak symmetry breaking while satisfying all LEP limits. In the simplest of such an extension, the next-to-minimal supersymmetric model, the lightest CP-even Higgs boson can decay into two pseudoscalars. In the scenario with the least fine-tuning the lightest CP-even Higgs boson has a mass of order 100 GeV. In order to escape LEP limits it must decay to a pair of the lightest CP-odd Higgs bosons with Br(h-->aa)>.7 and m_a<2m_b (so that a-->tau⁺tau^- or light quarks and gluons). The mass of the lightest CP-odd Higgs boson is controlled by the soft-trilinear couplings, A_lambda(m_Z) and A_kappa(m_Z). We identify the region of parameter space where this situation occurs and discuss how natural this scenario is. It turns out that in order to achieve m_a<2m_b with A_lambda(m_Z), A_kappa(m_Z) of order the typical radiative corrections, the required tuning of trilinear couplings needs not be larger than 5%–10%. Further, the necessity for this tuning can be eliminated in specific SUSY-breaking scenarios. Quite interestingly, Br(h-->aa) is typically above 70% in this region of parameter space and thus an appropriately large value requires no additional tuning.

©2007 The American Physical Society