Ultraviolet asymptotics of scalar and pseudoscalar correlators in hot Yang-Mills theory

Inspired by recent lattice measurements, we determine the short-distance (a > omega >> pi T) asymptotics of scalar (trace anomaly) and pseudoscalar (topological charge density) correlators at 2-loop order in hot Yang-Mills theory. The results are expressed in the form of an Operator Product Expansion. We confirm and refine the determination of a number of Wilson coefficients; however some discrepancies with recent literature are detected as well, and employing the correct values might help, on the qualitative level, to understand some of the features observed in the lattice measurements. On the other hand, the Wilson coefficients show slow convergence and it appears uncertain whether this approach can lead to quantitative comparisons with lattice data. Nevertheless, as we outline, our general results might serve as theoretical starting points for a number of perhaps phenomenologically more successful lines of investigation.Comment: 27 pages. v2: minor improvements, published versio

Next-to-leading order thermal spectral functions in the perturbative domain

Laine M, Vuorinen A, Zhu Y. Next-to-leading order thermal spectral functions in the perturbative domain. JHEP. 2011;2011(9): 84.Motivated by applications in thermal QCD and cosmology, we elaborate on ageneral method for computing next-to-leading order spectral functions forcomposite operators at vanishing spatial momentum, accounting for real, virtualas well as thermal corrections. As an example, we compute these functions(together with the corresponding imaginary-time correlators which can becompared with lattice simulations) for scalar and pseudoscalar densities inpure Yang-Mills theory. Our results may turn out to be helpful innon-perturbative estimates of the corresponding transport coefficients, whichare the bulk viscosity in the scalar channel and the rate of anomalouschirality violation in the pseudoscalar channel. We also mention links tocosmology, although the most useful results in that context may come from afuture generalization of our methods to other correlators

Population and distribution of beavers Castor fiber

1. A century ago, overhunting had reduced Eurasian beaver Castor fiber populations to c. 1200 animals in scattered refugia from France to Mongolia. Reintroductions and natural spread have since restored the species to large areas of its original range. Population has more than tripled since the first modern estimate in 1998; the minimum estimate is now c. 1.5 million. 2. Range expansion 2000–2020 has been rapid, with large extensions in western and south-central Europe, southern Russia, and west and central Siberia. Beavers are now re-established in all countries of their former European range except for Portugal, Italy, and the southern Balkans; they occur broadly across Siberia to Mongolia, with scattered populations father east. About half of the world population lives in Russia. Populations appear to be mature in much of European Russia, Belarus, the Baltic States, and Poland. 3. There is a significant population of North American beaver Castor canadensis in Finland and north-west Russia. Most other 20th-Century introductions of this species have become extinct or been removed. 4. Recent DNA studies have improved understanding of Castor fiber population prehistory and history. Two clades, east and west, are extant; a third ‘Danube’ clade is extinct. Refugial populations were strongly bottlenecked, with loss of genetic diversity through genetic drift. 5. Future range extension, and large increases in populations and in impacts on freshwater systems, can be expected. Beavers are now recolonising densely populated, intensely modified, low-relief regions, such as England, the Netherlands, Belgium, and north-west Germany. They will become much more common and widespread there in coming decades. As beavers are ecosystem engineers with profound effects on riparian habitats, attention to integrating beaver management into these landscapes using experience gained in other areas – before the rapid increase in population densities and impacts occurs – is recommended. beaver, Castor fiber, Castor canadensis, distribution, Eurasia, population, reintroductionpublishedVersio