A Scenario for Contact Interactions at HERA

The four fermion contact interactions, required to explain the anomalous HERA result, could come from the exchange of new heavy (probably composite) resonances. Depending on their charges and quantum numbers, one gets different scenarios and finds that many of these configurations are unsuitable. For example, new neutral resonances seems to be disfavored by the data coming from the TEVATRON, LEP 2 and atomic parity violation. These experiments allow only few helicity combinations that cannot arise from neutral currents in a natural way. On the contrary, a global large symmetry SU(8) * SU(8) (which is contained in SU(16)) embeds some lepto-quarks of spin 1 that could give suitable four fermion interactions (compatible with all other experiments) if these resonances are the lightest new (probably composite) states with a mass comparable to the scale of the contact interactions.Comment: 8 pages, LaTeX, no figur

Production of gauge bosons plus jets in hadronic collisions

A computational strategy and a collection of codes are presented for studying multiparticle final states in hard hadronic collisions.Comment: 4 pages, 2 figures, talk given at ICHEP'02 (Amsterdam, 24-31 July 2002

Electroweak Precision Tests: A Concise Review

1. Introduction 2. Status of the Data 3. Precision Electroweak Data and the Standard Model 4. A More General Analysis of Electroweak Data 4.1 Basic Definitions and Results 4.2 Experimental Determination of the Epsilon Variables 4.3 Comparing the Data with the Minimal Supersymmetric Standard Model 5. Theoretical Limits on the Higgs Mass 6. ConclusionComment: Submitted to Int. Journal of Modern Physics

The tau forward-backward Asymmetry within Grand Unified Theories

We will study some possible non universal corrections that could affect single measurements of the Weinberg angle sin^2(theta) (leaving the full average essentially unchanged). We will concentrate on the class of the models that introduces a new light gauge boson and an extended Higgs sector, but we restrict the Higgs charges choice in order to automatically achieve zero mixing at the tree level between the Z_0 and the Z'. This will more naturally keep small the universal effects with a relatively light Z', but it will imply only vector-like coupling between this boson and the standard fermions. A SO(10) gauge boson which distinguishes between families can have such properties and could explain a deviation in the tau forward-backward asymmetry without affecting the tau polarization measurements at LEP.Comment: 10 pages, Late

How to Integrate Divergent Integrals: a Pure Numerical Approach to Complex Loop Calculations

Loop calculations involve the evaluation of divergent integrals. Usually [1] one computes them in a number of dimensions different than four where the integral is convergent and then one performs the analytical continuation and considers the Laurent expansion in powers of epsilon =n-4. In this paper we discuss a method to extract directly all coefficients of this expansion by means of concrete and well defined integrals in a five dimensional space. We by-pass the formal and symbolic procedure of analytic continuation; instead we can numerically compute the integrals to extract directly both the coefficient of the pole 1/epsilon and the finite part.Comment: 13 pages, 1 Postscript figur