Counting eigenvalues in domains of the complex field

A procedure for counting the number of eigenvalues of a matrix in a region surrounded by a closed curve is presented. It is based on the application of the residual theorem. The quadrature is performed by evaluating the principal argument of the logarithm of a function. A strategy is proposed for selecting a path length that insures that the same branch of the logarithm is followed during the integration. Numerical tests are reported for matrices obtained from conventional matrix test sets.Comment: 21 page

Minimal string-scale unification of gauge couplings

We look for the minimal particle content which is necessary to add to the standard model in order to have a complete unification of gauge couplings and gravity at the weakly coupled heterotic string scale. Using the current precision electroweak data, we find that the presence of a vector-like fermion at an intermediate scale and a non-standard hypercharge normalization are in general sufficient to achieve this goal at two-loop level. If one requires the extra matter scale to be below the TeV scale, then it is found that the addition of three vector-like fermion doublets with a mass around 700 GeV yields a perfect string-scale unification, provided that the affine levels are kY=13/3, k2=1 and k3=2, as in the SU(5) X SU(5) string-GUT. Furthermore, if supersymmetry is broken at the unification scale, the Higgs mass is predicted in the range 125 GeV - 170 GeV, depending on the precise values of the top quark mass and tan(beta) parameter.Comment: 12 pages, 2 figures, references updated and comments added, final version to appear in Phys. Lett.

The Evolution of High Incomes in Canada, 1920-2000

This paper presents new homogeneous series on top shares of income from 1920 to 2000 in Canada using personal income tax return data. Top income shares display a U-shaped pattern over the century, with a precipitous drop during World War II, followed by a slower decline until 1970. Since the late 1970s, top income shares have been increasing steadily and the very top shares are now as high as in the pre-war era. As in the United States, the recent increase in top income shares is the consequence of a surge in top wages and salaries. The parallel evolution of top income shares in Canada and the United States, associated with much more modest marginal tax rate cuts in Canada, suggests that the upward trend in top shares in Canada since the late 1970s cannot be explained by tax cuts. Further evidence suggests that the upward trend in Canada derives from the United States, perhaps because many Canadians have an emigration option.income share

Consumption insurance and vulnerability to poverty

This paper synthesizes the results of five studies using household panel data from Bangladesh, Ethiopia, Mali, Mexico and Russia, which examine the extent to which households are able through formal and/or informal arrangements to insure their consumption from specific economic shocks and fluctuations in their real income. Building on the recent literature of consumption smoothing and risk sharing, the degree of consumption insurance is defined by the degree to which the growth rate of household consumption covaries with the growth rate of household income. All the case studies show that food consumption is better insured than nonfood consumption from idiosyncratic shocks. Adjustments in nonfood consumption appear to act as a mechanism for partially insuring ex-post the consumption of food from the effects of income changes. Food consumption is also more likely to be covered by informal insurance arrangements at the community level than nonfood consumption. Linkages among consumption variability, the level of household consumption, the incidence of poverty, and the probability of being ever poor and the proportion of time spent in poverty are also explored for Bangladesh, Ethiopia, and Russia. All the case studies also show that households use a portfolio of risk-coping strategies, but that different types of households may have differential ability to use these strategies. In particular, poorer households may be less able to use mechanisms that rely to initial wealth as collateral. In this regard, public transfer programs may have a more redistributive effect.

The Evolution of High Incomes in Canada, 1920-2000

This paper presents new homogeneous series on top shares of income from 1920 to 2000 in Canada using personal income tax return data. Top income shares display a U-shaped pattern over the century, with a precipitous drop during World War II, followed by a slower decline until 1970. Since the late 1970s, top income shares have been increasing steadily and the very top shares are now as high as in the pre-war era. As in the United States, the recent increase in top income shares is the consequence of a surge in top wages and salaries. As a result, series on the composition of incomes within the top income groups from 1946 to 2000 show a dramatic increase in the share of wages and salaries. The parallel evolution of top income shares in Canada and the United States, associated with much more modest marginal tax rate cuts in Canada, suggests that the upward trend in top shares in Canada since the late 1970s cannot be explained by tax cuts. Further evidence suggests that the upward trend in Canada derives from the United States, perhaps because many Canadians have an emigration option. A data appendix for this paper is available.

Consumption insurance and vulnerability to poverty : a synthesis of the evidence from Bangladesh, Ethiopia, Mali, Mexico and Russia

This paper brings together some of the empirical work conducted by IFPRI researchers which investigates linkages among the degree of consumption insurance, households'vulnerability to poverty, and household use of formal and informal coping mechanisms using the same empirical approach in five different countries.Environmental Economics&Policies,Inequality,Economic Theory&Research,Financial Intermediation,Rural Poverty Reduction