Precise interpretations of traditional fine-tuning measures

Abstract

We uncover two precise interpretations of traditional electroweak fine-tuning (FT) measures that were historically missed. : the traditional FT measure shows the change in plausibility of a model in which a parameter was exchanged for the Z boson mass relative to an untuned model in light of the Z boson mass measurement. the traditional FT measure shows the exponential of the extra information, measured in nats, relative to an untuned model that you must supply about a parameter in order to fit the Z mass. We derive the mathematical results underlying these interpretations, and explain them using examples from weak scale supersymmetry. These new interpretations allow us to rigorously define FT in particle physics and beyond, shed fresh light on the status of extensions to the Standard Model and, lastly, allow us to precisely reinterpret historical and recent studies using traditional FT measures. Published by the American Physical Society 2025