65,814 research outputs found
Nonequilibrium chiral perturbation theory and disoriented chiral condensates
We analyse the extension of Chiral Perturbation Theory to describe a meson
gas out of thermal equilibrium. For that purpose, we let the pion decay
constant be a time-dependent function and work within the Schwinger-Keldysh
contour technique. A useful connection with curved space-time QFT allows to
consistently renormalise the model, introducing two new low-energy constants in
the chiral limit.
We discuss the applicability of our approach within a Relativistic Heavy-Ion
Collision environment. In particular, we investigate the formation of
Disoriented Chiral Condensate domains in this model, via the parametric
resonance mechanism.Comment: Talk given in ``Hadron Physics: Effective Theories of Low Energy
QCD'', Coimbra, Portugal, Sept. 10-15 1999. Uses aipproc.sty, available at
ftp://ftp.aip.org/ems/tex/macros/proceedings/6x
Pion production in nonequilibrium Chiral perturbation Theory
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
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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