Three-Loop Electroweak Correction to the Rho Parameter in the Large Higgs Mass Limit

We present an analytical calculation of the leading three-loop radiative correction to the rho-parameter in the Standard Model in the large Higgs mass limit. This correction, of order g^6 m_H^4/M_W^4, is opposite in sign to the leading two-loop correction of order g^4 m_H^2/M_W^2. The two corrections cancel each other for a Higgs mass of approximately 480 GeV. The result shows that it is extremely unlikely that a strongly interacting Higgs sector could fit the data of electroweak precision measurements.