Natural Tuning: Towards A Proof of Concept

TL;DR

This paper introduces toy quantum theories demonstrating a new form of naturalness where low-energy physics appears tuned but does not require fine-tuning across all scales, challenging traditional naturalness concepts.

Contribution

It constructs UV complete models with asymptotic fragility, providing a proof of concept for a refined notion of naturalness without fixed points.

Findings

Low energy physics can be tuned without fine-tuning at all scales.

Asymptotic fragility replaces fixed points in UV physics.

Observation of unprotected scalars at LHC would support this scenario.

Abstract

The cosmological constant problem and the absence of new natural physics at the electroweak scale, if confirmed by the LHC, may either indicate that the nature is fine-tuned or that a refined notion of naturalness is required. We construct a family of toy UV complete quantum theories providing a proof of concept for the second possibility. Low energy physics is described by a tuned effective field theory, which exhibits relevant interactions not protected by any symmetries and separated by an arbitrary large mass gap from the new "gravitational" physics, represented by a set of irrelevant operators. Nevertheless, the only available language to describe dynamics at all energy scales does not require any fine-tuning. The interesting novel feature of this construction is that UV physics is not described by a fixed point, but rather exhibits asymptotic fragility. Observation of additional unprotected scalars at the LHC would be a smoking gun for this scenario. Natural tuning also favors TeV scale unification.