Higgs mass constraints on a fourth family: Upper and lower limits on CKM mixing

Abstract

Limits on the Higgs boson mass restrict Cabibbo-Kobayashi-Maskawa quark-mixing matrix (CKM) mixing of a possible fourth family beyond the constraints previously obtained from precision electroweak data alone. Existing experimental and theoretical bounds on ${m}_{H}$ already significantly restrict the allowed parameter space. Zero CKM mixing is excluded and mixing of order ${\ensuremath{\theta}}_{\mathrm{Cabbibo}}$ is allowed. Upper and lower limits on 3--4 CKM mixing are exhibited as a function of ${m}_{H}$. 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.