Two Notions of Naturalness

  • Porter WilliamsEmail author
Part of the following topical collections:
  1. Naturalness, Hierarchy, and Fine-Tuning


My aim in this paper is twofold: (i) to distinguish two notions of naturalness employed in beyond the standard model (BSM) physics and (ii) to argue that recognizing this distinction has methodological consequences. One notion of naturalness is an “autonomy of scales” requirement: it prohibits sensitive dependence of an effective field theory’s low-energy observables on precise specification of the theory’s description of cutoff-scale physics. I will argue that considerations from the general structure of effective field theory provide justification for the role this notion of naturalness has played in BSM model construction. A second, distinct notion construes naturalness as a statistical principle requiring that the values of the parameters in an effective field theory be “likely” given some appropriately chosen measure on some appropriately circumscribed space of models. I argue that these two notions are historically and conceptually related but are motivated by distinct theoretical considerations and admit of distinct kinds of solution.


Naturalness Effective field theory Beyond the standard model Multiverse 



I would like to thank Tony Duncan, Michael Miller, and an insightful referee for this journal for helpful comments on an earlier draft, and Greg Anderson and Diego Castaño for helpful correspondence about the motivation for the notion of naturalness they introduced in [3]. I would also like to thank audiences at the Aachen workshop “Naturalness, Hierarchy, and Fine-tuning,” the University of Michigan workshop “Foundations of Modern Physics: the Standard Model after the Discovery of the Higgs Boson,” and at Balliol College, Oxford for their valuable feedback.


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Authors and Affiliations

  1. 1.Department of PhilosophyUniversity of Southern CaliforniaLos AngelesUSA

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