Higgs Mass Constraints on a Fourth Family: Upper and Lower Limits on CKM Mixing

TL;DR

This paper investigates how Higgs boson mass limits constrain the mixing between a potential fourth quark family and the known three, providing bounds on CKM mixing angles based on electroweak data.

Contribution

It establishes upper and lower bounds on 3-4 CKM mixing as a function of the Higgs mass, extending previous constraints with new electroweak fit analyses.

Findings

Zero CKM mixing is excluded.

Mixing of order the Cabibbo angle is allowed.

Bounds depend on Higgs mass and input parameters.

Abstract

Limits on the Higgs boson mass restrict CKM mixing of a possible fourth family beyond the constraints previously obtained from precision electroweak data alone. Existing experimental and theoretical bounds on the Higgs mass already significantly restrict the allowed parameter space. Zero CKM mixing is excluded and mixing of order the Cabibbo angle is allowed. Upper and lower limits on 3-4 CKM mixing are exhibited as a function of the Higgs mass. We use the default inputs of the Electroweak Working Group and also explore the sensitivity of both the three and four family fits to alternative inputs.