The Effective Weak Mixing Angle in the MSSM.pdf

a r X i v : h e p - p h / 9 8 0 1 4 2 5 v 3 2 0 J u n 1 9 9 8 hep-ph/9801425 THE EFFECTIVE WEAK MIXING ANGLE IN THE MSSM A. DEDES1, A. B. LAHANAS2 and K. TAMVAKIS1 1Division of Theoretical Physics, University of Ioannina, GR-45110, Greece 2Physics Department, Nuclear and Particle Physics Section University of Athens, Athens 157 71, Greece Abstract The predictions of the MSSM are discussed in the light of recent LEP and SLD precision data. The full supersymmetric one loop corrections to the effective weak mixing angle, experimentally determined in LEP and SLD experiments, are considered. It is demonstrated, both analytically and nu- merically, that, potentially dangerous, large logarithmic sparticle corrections are cancelled. The relative difference factor ?k between the mixing angle defined as a ratio of couplings and the experimentally obtained angle is dis- cussed. It is found that ?k is dominated by the oblique corrections, while the non-oblique overall supersymmetric EW and SQCD corrections are negligible. The comparison of the MSSM with radiative electroweak symmetry breaking to the LEP+SLD precision data indicates that rather large values of the soft breaking parameter M1/2 in the region greater than 500 GeV are preferred. January 1998 E-mails : adedes@cc.uoi.gr, alahanas@atlas.uoa.gr, tamvakis@cc.uoi.gr I. INTRODUCTION The electroweak mixing angle sin2 θW , defined as a ratio of gauge couplings, provides a convenient means to test unification in unified extensions of the Standard Model (SM) [1]. This quantity is not directly measured in experiments. Instead, LEP and SLD studies employ an effective coupling sin2 θleptoneff determined from on resonance asymmetries whose value is known with excellent accuracy [2–5]. This effective mixing angle has been studied in detail in the context of the SM at the one loop level in various renormalization schemes with the dominant two loop heavy top contributions and three loop QCD effects taken into account [4–8]. Due