Supersymmetry, Naturalness, and Light Higgsinos

Understand

We compare and contrast three different sensitivity measures, $\Delta_{EW}^{-1}$, $\Delta_{HS}^{-1}$ and $\Delta_{BG}^{-1}$ that have been used in discussions of fine-tuning.

• We argue that though not a fine-tuning measure, $\Delta_{EW}$, which is essentially determined by the particle spectrum, is important because $\Delta_{EW}^{-1}$ quantifies the minimum fine-tuning present in any theory with a specified spectrum.
• We emphasize the critical role of incorporating correlations between various model parameters in discussions of fine-tuning.
• We provide toy examples to show that if we can find high scale theories with specific correlations amongst parameters, the value of the traditional fine-tuning measure $\Delta_{BG}^{-1}$ (which differs significantly from $\Delta_{HS}^{-1}$ only when these correlations are important) would be close to $\Delta_{EW}^{-1}$.