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

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.