Correlation Dynamics of Yukawa-theory in 1+1 dimensions

Using the method of correlation dynamics we investigate the properties of a field-theory for fermions and scalar bosons coupled via a Yukawa interaction. Within this approach, which consists in an expansion of full equal-time Green functions into connected equal-time Green functions and a corresponding truncation of the hierarchy of equations of motion we carry out calculations up to 4th order in the connected Green functions and evaluate the effective potential of the theory in 1+1 dimensions on a torus. Comparing the different approximations we find a strong influence of the connected 4-point functions on the properties of the system.Comment: LaTeX, 38 pages, 12 figure

Shear Viscosity in the O(N) Model

We compute the shear viscosity in the O(N) model at first nontrivial order in the large N expansion. The calculation is organized using the 1/N expansion of the 2PI effective action (2PI-1/N expansion) to next-to-leading order, which leads to an integral equation summing ladder and bubble diagrams. We also consider the weakly coupled theory for arbitrary N, using the three-loop expansion of the 2PI effective action. In the limit of weak coupling and vanishing mass, we find an approximate analytical solution of the integral equation. For general coupling and mass, the integral equation is solved numerically using a variational approach. The shear viscosity turns out to be close to the result obtained in the weak-coupling analysis.Comment: 37 pages, few typos corrected; to appear in JHE

The QGP phase in relativistic heavy-ion collisions

The dynamics of partons, hadrons and strings in relativistic nucleus-nucleus collisions is analyzed within the novel Parton-Hadron-String Dynamics (PHSD) transport approach, which is based on a dynamical quasiparticle model for partons (DQPM) matched to reproduce recent lattice-QCD results - including the partonic equation of state - in thermodynamic equilibrium. The transition from partonic to hadronic degrees of freedom is described by covariant transition rates for the fusion of quark-antiquark pairs or three quarks (antiquarks), respectively, obeying flavor current-conservation, color neutrality as well as energy-momentum conservation. The PHSD approach is applied to nucleus-nucleus collisions from low SIS to RHIC energies. The traces of partonic interactions are found in particular in the elliptic flow of hadrons as well as in their transverse mass spectra.Comment: To be published by Springer in Proceedings of the International Symposium on `Exciting Physics', Makutsi-Range, South Africa, 13-20 November, 201

Umweltverträglichkeitsprüfung in Brasilien

Brasilien stand schon immer im internationalen Rampenlicht ökologischer Besorgnisse, vor allem, wenn man an die Gefährdung der amazonischen Regenwald-Ökosysteme, an gigantische Staudammbauten oder Großprojekte des Straßenbaus und der Erzgewinnung denkt. Die UNCED-Umweltkonferenz im Juni 1992 lenkte ein weiteres Mal den Blick auf die Umweltverhältnisse in diesem Land, in erfreulicher Differenzierung: Wurde doch wahrgenommen, daß auch und gerade in den Industrie- und Ballungsregionen des Landes die Umweltqualität bereits derart schlecht geworden ist, daß die Lebens- und Produktionsverhältnisse ernsthaft bedroht sind. Die Situation in São Paulo und in der benachbarten Industrieregion im Vale de Cubatão sind nur ein Beispiel dafür. Weniger bekannt dürfte jedoch sein, daß die Umweltgesetzgebung in Brasilien durchaus dem Standard moderner Industrieländer vergleichbar ist und Brasilien dies auch auf der UNCED-Konferenz durch die Unterschriften unter die verschiedenen Dokumente zu Klima, Biodiversität usw. dokumentiert hat. Dieser Beitrag will am Beispiel der Umweltverträglichkeitsprüfung zeigen, wie sich politisches Wollen gesetzgeberische Absicht und verwaltungsmäßige Umsetzung der Vorschriften den Umweltproblemen Brasiliens in der täglichen Praxis stellen. Am Beispiel der paranaensischen Landesumweltbehörde IAP (Instituto Ambiental de Paraná, vormals SUREHMA – Superintendencia dos Recursos Hidricos e Meio Ambiente) werden Grundlagen, Ablaufschema und Probleme bei der Anwendung und Umsetzung der UVP im Planfeststellungsverfahren dargestellt und diskutiert. Dieser Beitrag ist innerhalb eines Projektes der Technischen Zusammenarbeit im Umweltbereich zwischen Brasilien und der Bundesrepublik Deutschland entstanden, die unter dem Titel „Umweltauswirkungen von Staudammvorhaben“ seit 1987 vom bereits erwähnten IAP und der GTZ (Deutsche Gesellschaft für Technische Zusammenarbeit GmbH) im Auftrag des Bundesministeriums für wirtschaftliche Zusammenarbeit durchgeführt wird

Tachyonic preheating using 2PI-1/N dynamics and the classical approximation

We study the process of tachyonic preheating using approximative quantum equations of motion derived from the 2PI effective action. The O(N) scalar (Higgs) field is assumed to experience a fast quench which is represented by an instantaneous flip of the sign of the mass parameter. The equations of motion are solved numerically on the lattice, and the Hartree and 1/N-NLO approximations are compared to the classical approximation. Classical dynamics is expected to be valid, since the occupation numbers can rise to large values during tachyonic preheating. We find that the classical approximation performs excellently at short and intermediate times, even for couplings in the larger region currently allowed for the SM Higgs. This is reassuring, since all previous numerical studies of tachyonic preheating and baryogenesis during tachyonic preheating have used classical dynamics. We also compare different initializations for the classical simulations.Comment: 32 pages, 21 figures. Published version: Some details added, section added, references added, conclusions unchange

Hard gluon damping in hot QCD

The gluon collisional width in hot QCD plasmas is discussed with emphasis on temperatures near $T_c$, where the coupling is large. Considering its effect on the entropy, which is known from lattice calculations, it is argued that the width, which in the perturbative limit is given by $\gamma \sim g^2 \ln(1/g) T$, should be sizeable at intermediate temperatures but has to be small close to $T_c$. Implications of these results for several phenomenologically relevant quantities, such as the energy loss of hard jets, are pointed out.Comment: uses RevTex and graphic

The effect of memory on relaxation in a scalar field theory

We derive a kinetic equation with a non-Markovian collision term which includes a memory effect, from Kadanoff-Baym equations in $\phi^4$ theory within the three-loop level for the two-particle irreducible (2PI) effective action. The memory effect is incorporated into the kinetic equation by a generalized Kadanoff-Baym ansatz.Based on the kinetic equations with and without the memory effect, we investigate an influence of this effect on decay of a single particle excitation with zero momentum in 3+1 dimensions and the spatially homogeneous case. Numerical results show that, while the time evolution of the zero mode is completely unaffected by the memory effect due to a separation of scales in the weak coupling regime, this effect leads first to faster relaxation than the case without it and then to slower relaxation as the coupling constant increases.Comment: 12 pages, 6 eps figure

Qualidade do leite em rebanhos do Rio Grande do Sul no período de primavera.

A qualidade do leite cru tem sido um grande desafio para produtores de leite e para a indústria de laticínios. Propriedades leiteiras estão sendo caracterizadas através de questionário quanto ao ambiente produtivo, práticas de manejo, e outros.Editora técnica Claudia Cristina Gulias Gomes