Bose-Einstein Correlations from Opaque Sources

Bose-Einstein correlations in relativistic heavy ion collisions are very different for opaque sources than fortransparent ones. The Bose-Einstein radius parameters measured in two-particle correlation functions depend sensitively on the mean free path of the particles. In particular we find that the outward radius for an opaque source is smaller than the sidewards radius for sufficiently short duration of emission. A long duration of emission can compensate the opacity reduction of the longitudinal radius parameter and explain the experimental measurements of very similar side- and outward radius parameters.Comment: additional material included, 8 pages, revtex, epsfig, 2 figure included, manuscript also available at http://www.nbi.dk/~vischer/publications.htm

Fluctuations and HBT Scales in Relativistic Nuclear Collisions

Bose-Einstein correlations in relativistic heavy ion collisions are examined in a general model containing the essential features of hydrodynamical, cascade as well as other models commonly employed for describing the particle freeze-out. In particular the effects of longitudinal and transverse expansion, emission from surfaces moving in time, the thickness of the emitting layer varying from surface to volume emission and other effects are studied. Model dependences of freeze-out sizes and times are discussed and compared to recent $Pb+Pb$ data at 160A$\cdot$GeV.Comment: 9 pages, revtex, epsfig, 2 figure included, manuscript also available at http://www.nbi.dk/~vischer/publications.htm

Human Capital and Growth: Specification Matters

This paper suggests that the weak empirical effect of human capital on growth in existing cross-country studies is partly the result of an inappropriate specification that does not account for the different channels through which human capital aspects growth. A systematic replication of earlier results from the literature shows that both, initial levels and changes in human capital, have positive growth effects, while in isolation, each channel often appears insignificant. Studies that do not account for both channels might underestimate the effect of human capital due to convergence in human capital, in particular when measuring human capital in log average years of schooling. This study therefore complements alternative explanations for the weak growth effects of human capital based on outlier observations and measurement issues.Human Capital, Growth Regressions, Specification.

Human Capital and Growth: Specification Matters

This paper suggests that the weak empirical effect of human capital on growth in existing cross-country studies is partly the result of an inappropriate specification that does not account for the different channels through which human capital affects growth. A systematic replication of earlier results from the literature shows that both, initial levels and changes in human capital, have positive growth effects, while in isolation, each channel often appears insignificant. Moreover, the effects are heterogeneous across countries with different levels of development. The results suggest that the effect of human capital is likely to be underestimated in empirical specifications that do not account for both channels. This study therefore complements alternative explanations for the weak growth effects of human capital based on outlier observations and measurement issues.human capital, growth regressions, specification

Dynamical Formation of Disoriented Chiral Condensates

We study the dynamical formation of disoriented chiral condensates in very high energy nucleus-nucleus collisions using Bjorken hydrodynamics and relativistic nucleation theory. It is the dynamics of the first order confinement phase transition which controls the evolution of the system. Every bubble or fluctuation of the new, hadronic, phase obtains its own chiral condensate with a probability determined by the Boltzmann weight of the finite temperature effective potential of the linear sigma model. We evaluate domain size and chiral angle distributions, which can be used as initial conditions for the solution of semiclassical field equations.Comment: 17 pages, latex and 10 ps figures available at http://www.nbi.dk/~vischer/dcc.htm