The Natural Composite Higgs

TL;DR

This paper discusses a natural composite Higgs model based on the SU(5)/SO(5) coset, which fits current LHC data well and offers a natural explanation for the Higgs boson mass and weak scale, with distinctive collider signatures.

Contribution

It presents a concrete SU(5)/SO(5) composite Higgs model that improves fit to LHC data and achieves naturalness without fine-tuning, highlighting the role of UV-sensitive loops and exotic scalars.

Findings

Enhanced fit to LHC Higgs data compared to minimal models

Natural explanation of the Higgs mass and weak scale

Model-dependent collider signatures with exotic scalars

Abstract

The discovery of the Higgs boson has put considerable pressure on theories that aim to solve the hierarchy problem. Scenarios in which the Higgs is a pseudo Nambu-Goldstone boson (NGB) of some new strong dynamics must possess a number of non-generic features in order to pass the progressively stringent collider bounds and simultaneously meet our naturalness criteria. Among these features are the existence of light fermionic partners of the top quark and an efficient collective breaking of the Nambu-Goldstone symmetry. The top partners have to be not only parametrically lighter than the other composites, but also weakly coupled to them in order to suppress unwanted flavor-violating effects. A Natural pseudo-NGB Higgs model should also be able to fit the LHC Higgs data without fine-tuning. Among theories with comparable compositeness scales, those that predict smaller corrections in the Higgs couplings to the standard model particles are therefore preferred. A concrete implementation of these ingredients is discussed in a scenario based on the coset SU(5)/SO(5). The fit to the current LHC Higgs data is significantly improved compared to the minimal scenarios, and a fully natural explanation of both the weak scale and the Higgs boson mass can be attained. An important role is played by an independent quartic Higgs coupling generated by UV-sensitive loops involving electroweak doublets mixing with the top partners. The collider signature of this framework is shown to be rather model-dependent; in particular, the exotic scalars can alter the phenomenology of the top partners at a qualitative level.