Sliding Naturalness: Cosmological Selection of the Weak Scale

TL;DR

This paper proposes a cosmological mechanism involving two light scalars to explain the electroweak hierarchy, compatible with standard inflation, and offers testable predictions for dark matter and collider experiments.

Contribution

It introduces a new cosmological solution to the hierarchy problem using weakly coupled scalars, decoupled from the strong-CP problem, with broad phenomenological implications.

Findings

Mechanism works with any standard inflationary sector.

Reproduces observed dark matter relic density.

Predicts testable signals in axion or fifth force searches.

Abstract

We present a cosmological solution to the electroweak hierarchy problem. After discussing general features of cosmological approaches to naturalness, we extend the Standard Model with two light scalars very weakly coupled to the Higgs and present the mechanism, which we recently introduced in a companion paper to explain jointly the electroweak hierarchy and the strong-CP problem. In this work we show that this solution can be decoupled from the strong-CP problem and discuss its possible implementations and phenomenology. The mechanism works with any standard inflationary sector, it does not require weak-scale inflation or a large number of e-folds, and does not introduce ambiguities related to eternal inflation. The cutoff of the theory can be as large as the Planck scale, both for the Cosmological Constant and for the Higgs sector. Reproducing the observed dark matter relic density fixes the couplings of the two new scalars to the Standard Model, offering a target to future axion or fifth force searches. Depending on the specific interaction of the scalars with the Standard Model, the mechanism either yields rich phenomenology at colliders or provides a novel joint solution to the strong-CP problem. We highlight what predictions are common to most realizations of cosmological selection of the weak scale and will allow to test this general framework in the near future.