# Very light dilaton and naturally light Higgs boson

## TL;DR

This paper explores a scale-invariant ultraviolet theory leading to a very light dilaton that naturally stabilizes the Higgs mass and could serve as dark matter, with testable predictions at the LHC.

## Contribution

It introduces a scenario where a light dilaton from scale invariance explains the Higgs mass hierarchy and proposes a dilaton-assisted composite Higgs model with observable signatures.

## Key findings

- Dilaton can be a dark matter candidate with mass between 1 eV and 10 keV.
- Ultraviolet scale can be much higher than the electroweak scale due to dilaton effects.
- Model predicts new particles potentially detectable at the LHC.

## Abstract

We study very light dilaton, arising from a scale-invariant ultraviolet theory of the Higgs sector in the standard model of particle physics. Imposing the scale symmetry below the ultraviolet scale of the Higgs sector, we alleviate the fine-tuning problem associated with the Higgs mass. When the electroweak symmetry is spontaneously broken radiatively \`a la Coleman-Weinberg, the dilaton develops a vacuum expectation value away from the origin to give an extra contribution to the Higgs potential so that the Higgs mass becomes naturally around the electroweak scale. The ultraviolet scale of the Higgs sector can be therefore much higher than the electroweak scale, as the dilaton drives the Higgs mass to the electroweak scale. We also show that the light dilaton in this scenario is a good candidate for dark matter of mass $m_D\sim 1~{\rm eV}-10~{\rm keV}$, if the ultraviolet scale is about $10-100~{\rm TeV}$. Finally we propose a dilaton-assisted composite Higgs model to realize our scenario. In addition to the light dilaton the model predicts a heavy ${\rm U}(1)$ axial vector boson and two massive, oppositely charged, pseudo Nambu-Goldstone bosons, which might be accessible at LHC.