Kaluza-Klein Thresholds and Regularization (In)dependence

We present a method to control the regularization scheme dependence in the running of couplings in Kaluza-Klein theories. Specifically we consider the scalar theory in five dimensions, assuming that one dimension is compactified and we study various regularization schemes in order to analyze concretely the regularization scheme dependence of the Kaluza-Klein threshold effects. We find that in one-loop order, although the $\beta$-functions are different for the different schemes, the net difference in the running of the coupling among the different schemes is very small for the entire range of energies. Our results have been extended to include more than one radii, and the gauge coupling unification is re-examined. Strings are also used as a regulator. We obtain a particular regularization of effective field theory which can accurately describe the string Kaluza-Klein threshold effects.Comment: 39 pages, 12 figures uses epsf.st

The Effective Weak Mixing Angle in the MSSM

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 numerically, that, potentially dangerous, large logarithmic sparticle corrections are cancelled. The relative difference factor \Delta k between the mixing angle defined as a ratio of couplings and the experimentally obtained angle is discussed. It is found that \Delta 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 M_{1/2} in the region greater than 500 GeV are preferred.Comment: 36 pages, 9 figures, references adde

Search for excited taus from Z\u3csup\u3e0\u3c/sup\u3e decays

\u3cp\u3eWe have searched for excited taus from Z\u3csup\u3e0\u3c/sup\u3e decay in the channels e\u3csup\u3e+\u3c/sup\u3ee\u3csup\u3e-\u3c/sup\u3e → τ\u3csup\u3e*+\u3c/sup\u3eτ\u3csup\u3e*-\u3c/sup\u3e → τ\u3csup\u3e+\u3c/sup\u3eτ\u3csup\u3e-\u3c/sup\u3eγ γ and e\u3csup\u3e+\u3c/sup\u3ee\u3csup\u3e-\u3c/sup\u3e → ττ\u3csup\u3e*\u3c/sup\u3e → τ\u3csup\u3e+\u3c/sup\u3eτ\u3csup\u3e-\u3c/sup\u3eγ, using the L3 detector at LEP. Using the τ\u3csup\u3e*\u3c/sup\u3e pair production channel, we can exclude a τ\u3csup\u3e*\u3c/sup\u3e up to a mass of 45.5 geV at 95% confidence level. We have also determined upper limits on the ττ\u3csup\u3e*\u3c/sup\u3eZ\u3csup\u3e0\u3c/sup\u3e and ττ\u3csup\u3e*\u3c/sup\u3eγ couplings as a function of m\u3csub\u3eτ*\u3c/sub\u3e up to 89.3 GeV.\u3c/p\u3