Using effective-Lagrangian techniques we perform a systematic survey of the lowest-dimension effective interactions through which heavy physics might manifest itself in present experiments. We do not restrict ourselves to special classes of effective interactions (such as "oblique" corrections). We compute the effects of these operators on all currently well-measured electroweak observables, both at low energies and at the Z resonance, and perform a global fit to their coefficients. Despite the fact that a great many operators arise in our survey, we find that most are quite strongly bounded by the current data. We use our-survey to systematically identify those effective interactions which are not well bounded by the data-these could very well include large new-physics contributions. Our results may also be used to efficiently confront specific models for new physics with the data, as we illustrate with an example.PACS number(s): 12.60. -i

The ST U formalism of Peskin and Takeuchi is an elegant method for encoding the measurable effects of new physics which couples to light fermions dominantly through its effects on electroweak boson propagation. However, this formalism cannot handle the case where the scale of new physics is not much larger than the weak scale. In this case three new parameters (V, W and X) are required. We perform a global fit to precision electroweak data for these six parameters. Our results differ from what is found for just ST U . In particular we find that the preference for S < 0 is not maintained.

The complex Busemann-Petty problem asks whether origin symmetric convex bodies in C n with smaller central hyperplane sections necessarily have smaller volume. We prove that the answer is affirmative if n ≤ 3 and negative if n ≥ 4.

We present the results of the gluino and scalar quark contribution to the flavor-changing top quark decay into a charm quark and a photon, gluon, or a Z0 boson within the minimal supersymmetric standard model. We include the mixing of the scalar partners of the left-and right-handed top quark. This mixing has several effects, the most important of which is to greatly enhance the cZ decay mode for large values of the soft SUSY-breaking scalar mass ms and to give rise to a GIM-like suppression in the cy mode for certain combinations of parameters. PACS number(s): 12.60.Jv, 14.65.Ha Recent experimental evidence of the top quark [I] makes its rare decay modes a promising test ground for the standard model (SM) and physics beyond the SM. The flavor-changing decay mode of the top quark was calculated within the SM in [2-61 and their branching ratioswere shown to be -10-l2 for t + CY, -10-12-10-13 for t + c Z and for t -+ cg in the top mass range 90-200 GeV, thus far away from experimental reach; this makes it a n excellent probe for models beyond the SM. Two-Higgs-doublet models (THDM's) were considered in [6,7], where it was shown that the decay rate is enhanced by several (3-4) orders of magnitude. Recently [8], the

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