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 ${\theta }_{\mathrm{Cabbibo}}$ 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.

• Received 6 July 2010

DOI:https://doi.org/10.1103/PhysRevD.82.035018