Hidden Sector Custodial Naturalness

TL;DR

This paper introduces a minimal model for Custodial Naturalness that addresses the electroweak hierarchy problem without extending the SM gauge group, featuring a new scalar singlet as a dark matter candidate and a high-scale UV completion.

Contribution

It proposes a novel minimal realization of Custodial Naturalness with reduced custodial symmetry and a scalar singlet, avoiding gauge group extensions and linking to dark matter and neutrino mass generation.

Findings

The model achieves electroweak scale generation at a UV scale of around 10^11 GeV.

The scalar singlet serves as a viable dark matter candidate produced via freeze-in.

Including neutrino masses can elevate the UV completion scale to the Planck scale.

Abstract

Custodial Naturalness is a recently introduced idea that combines conformal and scalar-sector custodial symmetry to address the electroweak (EW) scale hierarchy problem of the Standard Model (SM). We introduce a new model that realizes Custodial Naturalness without extension of the SM gauge group. The number of new dynamical degrees of freedom is minimized and the custodial symmetry is reduced to $\mathrm{SO}(5)$. This requires a new scalar singlet field that automatically is a good Dark Matter (DM) candidate, produced via freeze-in with moderate couplings. The most minimal scenario allows the quantum critical generation of the EW scale in a phenomenologically viable way requiring a UV completion at around $10^{11}\,\mathrm{GeV}$. Including ingredients for neutrino mass generation can push this scale to $M_{\mathrm{Pl}}$.