Constraining the scalar septet model through vector boson scattering

Understand

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.