Application of Renormalization Group Techniques to a Homogeneous Bose Gas at Finite Temperature

A homogeneous Bose gas is investigated at finite temperature using renormalization group techniques. A non--perturbative flow equation for the effective potential is derived using sharp and smooth cutoff functions. Numerical solutions of these equations show that the system undergoes a second order phase transition in accordance with universality arguments. We obtain the critical exponent $\nu =0.73$ to leading order in the derivative expansion.Comment: 20 pages, 6 Postscript figures, revte

Flexicurity – Labour Market Performance in Denmark

Unemployment is at a low and stable level in Denmark. This achievement is often attributed to the so-called flexicurity model combining flexible hiring and firing rules for employers with income security for employees. Whatever virtues this model may have, a low and stable unemployment rate is not automatically among them since the basic flexicurity properties were also in place during the 1970s and 1980s where high and persistent unemployment was prevalent. Labour market performance has changed due to a series of reforms during the 1990s, the main thrust of which were a shift from a passive focus of labour market policies to a more active focus on job search and employment. The policy tightened eligibility for unemployment benefits and their duration as well as introduced workfare elements into unemployment insurance and social policies in general. Thereby policy makers attempted to strengthen the incentive structure without taking resort to general benefit reductions. We argue that the workfare policies have played an important role running primarily via motivation/threat and wage effects. However, active labour market policies are resource demanding, and although the workfare reforms have improved cost effectiveness, there is still an issue as to whether the resources going into active labour market policies are used efficiently.

Flexicurity in Denmark

Arbeitsmarktflexibilisierung, Arbeitsmarktpolitik, Wirtschaftspolitische Wirkungsanalyse, Dänemark, Flexicurity, Labour market flexibility, Labour market policy, Economic policy analysis, Denmark

Tension moderation and fluctuation spectrum in simulated lipid membranes under an applied electric potential

We investigate the effect of an applied electric potential on the mechanics of a coarse grained POPC bilayer under tension. The size and duration of our simulations allow for a detailed and accurate study of the fluctuations. Effects on the fluctuation spectrum, tension, bending rigidity, and bilayer thickness are investigated in detail. In particular, the least square fitting technique is used to calculate the fluctuation spectra. The simulations confirm a recently proposed theory that the effect of an applied electric potential on the membrane will be moderated by the elastic properties of the membrane. In agreement with the theory, we find that the larger the initial tension the larger the effect of the electric potential. Application of the electric potential increases the amplitude of the long wavelength part of the spectrum and the bending rigidity is deduced from the short wavelength fluctuations. The effect of the applied electric potential on the bending rigidity is non-existent within error bars. However, when the membrane is stretched there is a point where the bending rigidity is lowered due to a decrease of the thickness of the membrane. All these effects should prove important for mechanosensitive channels and biomembrane mechanics in general

QED Thermodynamics at Intermediate Coupling

We discuss reorganizing finite temperature perturbation theory using hard-thermal-loop (HTL) perturbation theory in order to improve the convergence of successive perturbative approximations to the free energy of a gauge theory. We briefly review the history of the technique and present new results for the three-loop HTL-improved approximation for the free energy of QED. We show that the hard-thermal-loop perturbation reorganization improves the convergence of the successive approximations to the QED free energy at intermediate coupling, e ~ 2. The reorganization is gauge invariant by construction, and due to cancellation among various contributions, one can obtain a completely analytic result for the resummed thermodynamic potential at three loops.Comment: 8 pages, 3 figures, Proceedings contribution to "Three Days of Strong Interactions", Wroclaw (Poland), July 200

Three loop HTL perturbation theory at finite temperature and chemical potential

In this proceedings contribution we present a recent three-loop hard-thermal-loop perturbation theory (HTLpt) calculation of the thermodynamic potential for a finite temperature and chemical potential system of quarks and gluons. We compare the resulting pressure, trace anomaly, and diagonal/off-diagonal quark susceptibilities with lattice data. We show that there is good agreement between the three-loop HTLpt analytic result and available lattice data.Comment: 4 pages, 4 figure

Hard-loop dynamics of non-abelian plasma instabilities

I discuss recent advances in the understanding of non-equilibrium gauge field dynamics in plasmas which have particle distributions which are locally anisotropic in momentum space. In contrast to locally isotropic plasmas such anisotropic plasmas have a spectrum of soft unstable modes which are characterized by exponential growth of transverse (chromo)-magnetic fields at short times. The long-time behavior of such instabilities depends on whether or not the gauge group is abelian or non-abelian. Here I will report on recent numerical simulations which attempt to determine the long-time behavior of an anisotropic non-abelian plasma within hard-loop effective theory.Comment: 4 pages, 1 figure; Contribution to proceedings of Quark Matter 2005, Budapest, Hungary, Aug 4-9 200