63,125 research outputs found

    Pion production in nonequilibrium Chiral perturbation Theory

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    We apply the formalism of Chiral Perturbation Theory out of thermal equilibrium to describe explosive production of pions via the parametric resonance mechanism. To lowest order the lagrangian is that of the Nonlinear Sigma Model where the pion decay constant becomes a time-dependent function. This model alows for a consistent nonequilibrium formulation within the framework of the closed time path method, where one-loop effects can be systematically accounted for and renormalized. We work in the narrow resonance regime where there is only one resonant band. The present approach is limited to remain below the back-reaction time, although it accounts for nearly all the pion production during the typical plasma lifetime. The space and time components of the pion decay constant are also analyzed.Comment: 23 pages, 8 figures, RevTe

    Child health in rural Colombia: determinants and policy interventions

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    In this paper we study the determinants of child anthropometrics on a sample of poor Colombian children living in small municipalities. We focus on the influence of household consumption, and public infrastructure. We take into account the endogeneity of household consumption using two different sets of instruments: household assets and municipality average wage. We find that household consumption is an important determinant of child health. The importance of the effect is confirmed by the two different sets of instruments. We find that using ordinary least squares would lead to conclude that the importance of household consumption is much smaller than the instrumental variable estimates suggest. The presence of a public hospital in the municipality positively influences child health. The extent of the piped water network positively influences the health of children if their parents have at least some education. The number of hours of growth and development check-ups is also an important determinant of child health. We find that some of these results only show up once squared and interaction terms have been included in the regression. Overall, our estimates suggest that both public and private investments are important to improve child health in poor environments
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