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T: Teilchenphysik

T 307: Elektroschwache Wechselwirkung I

T 307.7: Vortrag

Freitag, 4. März 2005, 18:00–18:15, TU H2037

Three Loop Electroweak Correction to the Rho-parameter in the Large Higgs mass Limit — •Radja Boughezal, J.B Tausk, and J.J van der Bij — Albert-ludwigs Universitaet, Physikalisches Institut, Hermann Herder Strasse 3, 79104 Freiburg

Low energy obsevables are sensitive to the existence of heavy particles in the Standard model (SM) through radiative corrections, in particular, to the minimal SM Higgs boson. One of these low energy observables is the electroweak ρ-parameter which is a measure of the relative strengths of neutral and charged-current interactions in four-fermion processes at zero momentum transfer. The leading one and two-loops radiative corrections in the large Higgs mass limit grow like log(m_H²/M_W²) and m_H² respectively where m_H and M_W are the masses of the Higgs and W bosons. The 1-loop correction has a negative sign whereas the 2-loops one has a positive sign and is much smaller than the 1-loop correction for values of m_H less than 4 TeV. The leading 3-loop correction to the ρ-parameter, calculated in the large m_H limit grows like m_H⁴ and could be important for a heavy Higgs boson. If it turns out to be important and positive, this correction may cancel the 1-loop correction, which gives, after summing the 1, 2, and 3-loop corrections, a similar effect to the light Higgs boson one. This similarity makes it impossible, when comparing with the experimental value of ρ, to decide whether the Higgs boson is heavy or light. However our calculation for the leading 3-loop electroweak correction to the ρ-parameter in the large Higgs mass limit shows that this is not the case, the correction is negative and enhances the 1-loop correction instead of canceling it.