Yukawa-coupling corrections to scalar quark decays

Heavy squark decays into top and charginos or neutralinos could be an unexpected source of top quarks at hadron colliders. A detailed treatment of these processes is necessary for a reliable calculation of both the top quark production cross-section and the standard top quark branching ratio in the MSSM. Along this line we compute the electroweak corrections to the sbottom decays sbottom_a --> chargino_i top within the Yukawa coupling approximation. The calculation of these higher order contributions requires renormalization of both the bottom squark mixing angle and of tan(beta). This type of corrections gives the leading order electroweak effects at low and high tan(beta).Comment: 16 pages, LaTeX, 5 figures included using epsfig. Comments added, equation 25 corrected, labels of fig.2 corrected, references update

Top quark decay into charged Higgs boson in a general Two-Higgs-Doublet model: implications for the TEVATRON data

We analyze the unconventional top quark decay mode t -> H^+ b at the quantum level within the context of general Two-Higgs-Doublet models by including the full electroweak effects from the Yukawa couplings. The results are presented in the on-shell renormalization scheme with a physically well motivated definition of tan(beta). While the QCD corrections have been taken into account in the current experimental analyses of that decay, the electroweak effects have always been neglected. However, we find that they can be rather large and could dramatically alter the interpretation of the present data from the Tevatron collider. For instance, in large portions of the parameter space the electroweak effects prevent the Tevatron data from placing any bound at all to the charged Higgs mass for essentially any value of tan(beta).Comment: 11 pages, LaTeX, 4 figs included using epsfi

Looking for quantum SUSY signatures in top quark decays at hadron colliders

We discuss the supersymmetric quantum effects on top quark decays within the MSSM. It turns out that t-> H+ b is the most promising candidate for carrying large quantum SUSY signatures. As a result, the recent (tan(beta) M_H) exclusion plots presented by the CDF Collaboration should be thoroughly revised in the light of the MSSM.Comment: 6 pages, LaTeX, 1 figure included as a separate file, full postscript version avaliable at ftp://ftp.ifae.es/preprint/ft/uabft423.ps . Invited talk presented at the XVI International Workshop on Weak Interaction and Neutrinos (WIN 97), Capri, Italy, 22-28 June, 1997. To appear in the Proceedings. Postscript figure right-shifted to avoid overlapping with automatically positioned hep-number in postscript generatio

Adaptive waveform inversion: theory

Conventional full-waveform seismic inversion attempts to find a model of the subsurface that is able to predict observed seismic waveforms exactly; it proceeds by minimizing the difference between the observed and predicted data directly, iterating in a series of linearized steps from an assumed starting model. If this starting model is too far removed from the true model, then this approach leads to a spurious model in which the predicted data are cycle skipped with respect to the observed data. Adaptive waveform inversion (AWI) provides a new form of full-waveform inversion (FWI) that appears to be immune to the problems otherwise generated by cycle skipping. In this method, least-squares convolutional filters are designed that transform the predicted data into the observed data. The inversion problem is formulated such that the subsurface model is iteratively updated to force these Wiener filters toward zero-lag delta functions. As that is achieved, the predicted data evolve toward the observed data and the assumed model evolves toward the true model. This new method is able to invert synthetic data successfully, beginning from starting models and under conditions for which conventional FWI fails entirely. AWI has a similar computational cost to conventional FWI per iteration, and it appears to converge at a similar rate. The principal advantages of this new method are that it allows waveform inversion to begin from less-accurate starting models, does not require the presence of low frequencies in the field data, and appears to provide a better balance between the influence of refracted and reflected arrivals upon the final-velocity model. The AWI is also able to invert successfully when the assumed source wavelet is severely in error

Assesing the Impact of the Investment Climate on Productivity Using Firm-Level Data: Methodology and the Cases of Guatemala, Honduras, and Nicaragua

Developing countries are increasingly concerned about improving country competitiveness and productivity, as they face the increasing pressures of globalization and attempt to improve economic growth and reduce poverty. Among such countries, Investment Climate Assessments (ICA) have become a standard instrument for identifying key obstacles to country competitiveness and imputing their impact on productivity, in order to prioritize policy reforms for enhancing competitiveness. Given the survey objectives and the nature and limitations of the data collected, this report discusses the advantages and disadvantages of using different productivity measures based on data at the firm level. The main objective is to develop a methodology to appropriately estimate, in a robust manner, the productivity impact of the investment climate variables. To illustrate the use of this methodology, the report applies it to the data collected for ICAs in three countries: Guatemala, Honduras and Nicaragua. Observations in logarithms (logs) of the variables, and not in rates of growth, are pooled from all three countries. The econometric analysis is done with variables in logs to reduce the impact of measurement errors and allow inclusion of as many observations as possible since the “panel” data set is very unbalanced. Endogeneity of the production function inputs and of the investment climate variables is addressed by using a variant of the control function approach, based on individual firm information, and by aggregating investment climate variables by industry and region. It is shown that it is possible to get robust results for 10 different productivity measures, if one follows a consistent econometric methodology of specification and estimation. For policy analysis, the report strongly recommends using those results of investment climate variables on productivity that are robust for most of the productivity measures. Efficiency aspects of firms in each country are also analyzed. Finally, the results are decomposed to obtain country-specific impacts and establish corresponding priorities for policy reform. The actual estimates for the three countries show the level of significance of the impact of investment climate variables on productivity. Variables in several categories, red tape and infrastructure in particular, appear to account for over 30 percent of productivity. The policy implications are clear: investment climate matters enormously and the relative impact of the various investment climate variables indicates where reform efforts should be directed. Given the robustness of the results, it is argued that the econometric methodology of productivity analysis developed here ought to be used as a benchmark to assess productivity effects for other ICAs or surveys with firm-level data of similar characteristics