Transport Coefficients in Hot QCD

I give a physical explanation of what shear viscosity is, and what physics determines its value. Then I explain why determining the shear viscosity of the Quark-Gluon Plasma is interesting. I outline the leading-order calculation of the QGP shear viscosity (and baryon number diffusion constant), explaining why the quite complicated physics of parton splitting and Landau-Pomeranchuk-Migdal interference effects are required for its calculation. Then I briefly explore the range of applicability, emphasizing the importance of plasma instabilities.Comment: 10 pages, invited talk given at the conference "Strong and Electroweak Matter," Helsinki, Finland 16-19 June 200

Electroweak Bubble Wall Friction: Analytic Results

We present an entirely analytic, leading log order determination of the friction an electroweak bubble wall feels during a first order electroweak phase transition. The friction is dominated by W bosons, and gives a wall velocity parametrically ~ alpha_w, and numerically small, ~ .01 -- 0.1 depending on the Higgs mass.Comment: 8 pages, no figures. Slight revision of introduction: published version (JHEP

Climate change: carbon losses in the Alps

The response of the terrestrial carbon cycle to global change is one of the main uncertainties in current climate change predictions1. Most terrestrial carbon is held in soils as organic matter derived from the decay of plant material (Fig. 1). Soil organic matter accounts for roughly three times more carbon than living vegetation, and for more carbon than vegetation and the atmosphere combined. Because elevated atmospheric CO2 concentrations have a fertilizing effect on plant growth, anthropogenic CO2 emissions have triggered increases in the land carbon sink2. However, models predict that other factors — such as water and nutrients — will eventually become limiting to plant growth, and hence to the land carbon sink. In contrast, the turnover of soil organic matter producing CO2 is expected to increase as the Earth warms. As a result, simulations using coupled carbon–climate models predict that the land surface will become a net source of CO2 before the end of the century, leading to a feedback loop between climate and soil carbon losses: increased emissions of CO2 from soil organic matter will lead to enhanced warming, which may then feedback to cause further soil organic matter losses. Prietzel and colleagues3, writing in Nature Geoscience, now provide evidence that warming has already caused a decline in soil organic matter in the German Alps