The NMSSM Solution to the Fine-Tuning Problem, Precision Electroweak Constraints and the Largest LEP Higgs Event Excess

Abstract

We present an extended study of how the Next to Minimal Supersymmetric Model easily avoids fine-tuning in electroweak symmetry breaking for a SM-like light Higgs with mass in the vicinity of $100\gev$, as beautifully consistent with precision electroweak data, while escaping LEP constraints due to the dominance of $h\to aa$ decays with $m_a<2m_b$ so that $a\to \tauptaum$ or jets. The residual $\sim 10$ branching ratio for $h\to b\anti b$ explains perfectly the well-known LEP excess at $\mh\sim 100\gev$. Details of model parameter correlations and requirements are discussed as a function $\tan ({\hat{I}}^2)$. Comparisons of fine-tuning in the NMSSM to that in the MSSM are presented. We also discuss fine-tuning associated with scenarios in which the $a$ is essentially pure singlet, has mass $m_a>30\gev$, and decays primarily to $\gam\gam$ leading to an $h\to aa\to 4\gam$ Higgs signal.

26 pages, 37 figures, published version with minor text and reference improvements