# Constraining the scalar septet model through vector boson scattering

## TL;DR

This paper constrains the scalar septet model, an extension of the Standard Model Higgs sector, using vector boson scattering unitarity and LHC search results, highlighting differences from other custodial symmetry-preserving models.

## Contribution

It provides the first comprehensive high-mass and low-mass constraints on the scalar septet model using perturbative unitarity and collider data.

## Key findings

- High septet masses constrained by unitarity bounds.
- Lower masses constrained by LHC doubly-charged Higgs searches.
- Distinct features compared to other custodial symmetry models.

## Abstract

The scalar septet model extends the Standard Model Higgs sector by an isospin septet with hypercharge chosen to preserve $\rho \equiv M_W^2/M_Z^2 \cos^2\theta_W = 1$. In this paper we constrain the model at high septet masses using perturbative unitarity of longitudinal vector boson scattering amplitudes. We also apply the constraints from LHC searches for doubly-charged Higgs bosons produced in vector boson fusion, which constrain the model at lower septet masses. We point out some important differences between the septet model and extended Higgs models that preserve custodial symmetry in the scalar spectrum.