Mixing of pseudoscalar mesons and isospin symmetry breaking

Mixing of the pseudoscalar mesons is discussed in the quark-flavor basis with the hypothesis that the basis decay constants follow the pattern of particle state mixing. The divergences of the axial vector currents which embody the axial vector anomaly, combined with this hypothesis provide a calculational scheme for the parameters describing the mixing of the pion, eta and eta' mesons. Phenomenological applications of this mixing scheme are presented with particular interest focussed on isospin symmetry breaking in QCD estimated as eta and eta' admixtures to the pion. In contrast to previous work a possible difference in the basis decay constants f_u and f_d is considered and consequences of this potentially large effect on the strength of isospin symmetry breaking is discussed.Comment: 10 pages, (using LATEX with w-ijmpa.sty), invited talk presented at MESON 2004, 8th Intern. Workshop on Meson Production, Properties and Interaction

Lessons from cosmic history: The case for a linear star formation -- H2 relation

Observations show that star formation in galaxies is closely correlated with the abundance of molecular hydrogen. Modeling this empirical relation from first principles proves challenging, however, and many questions regarding its properties remain open. For instance, the exact functional form of the relation is still debated and it is also unknown whether it applies at z>4, where CO observations are sparse. Here, we analyze how the shape of the star formation -- gas relation affects the cosmic star formation history and global galaxy properties using an analytic model that follows the average evolution of galaxies in dark matter halos across cosmic time. We show that a linear relation with an H2 depletion time of ~2.5 Gyr, as found in studies of nearby galaxies, results in good agreement with current observations of galaxies at both low and high redshift. These observations include the evolution of the cosmic star formation rate density, the z~4-9 UV luminosity function, the evolution of the mass -- metallicity relation, the relation between stellar and halo mass, and the gas-to-stellar mass ratios of galaxies. In contrast, the short depletion times that result from adopting a highly super-linear star formation -- gas relation lead to large star formation rates, substantial metal enrichment (~0.1 solar), and low gas-to-stellar mass ratios already at z~10, in disagreement with observations. These results can be understood in terms of an equilibrium picture of galaxy evolution in which gas inflows, outflows, and star formation drive the metallicities and gas fractions toward equilibrium values that are determined by the ratio of the accretion time to the gas depletion time. In this picture, the cosmic modulation of the accretion rate is the primary process that drives the evolution of stellar masses, gas masses, and metallicities of galaxies from high redshift until today.Comment: 22 pages, 13 figures, minor revision after referee repor

The Unemployment Effect of Exchange Rate Volatility in Industrial Countries

Using data on 17 industrial countries from 1982 to 2003 and controlling for a wide array of factors, this paper finds that higher exchange rate volatility increases the unemployment rate. The magnitude of the effect is small. The results are robust to variations in specification.exchange rate volatility; unemployment

Organic data network: Harmonising organic market data collection in Europe

This contribution emerged as part of the collaborative project “Data network for better European organic market information” carried out in the 7th Framework Programme of the EU. Data from an online and a telephone survey among organic market data collectors form the basis for the analysis of the current situation of statistics on organic market data. The results reveal a heterogeneous picture, because organic market growth and data collection within the organic food sector have developed differently throughout Europe. Building on the survey results, the quality of data collection approaches is evaluated through the application of the data quality dimensions relevance, accuracy, comparability, coherence, accessibility/clarity, and timeliness/punctuality (Eurostat, 2009). Thereby best practice examples are identified and used for the elaboration of guidelines for the harmonisation of organic market data collection in Europe