Infrared exponents of Yang-Mills theory

In this talk I summarise recent results on the infrared exponents of SU($N_c$)-Yang-Mills theory. I discuss a self-consistent power law solution for the Dyson-Schwinger equations for general 1PI-Greens functions in the infrared. The corresponding running coupling has a fixed point at zero momentum, which turns out to be universal and gauge invariant within a class of transverse gauges. When calculated on a torus the infrared exponents of the ghost and gluon propagators differ from the corresponding continuum solutions. They agree, however, well with results from lattice calculations.Comment: 6 pages, 3 figures, talk presented at Lattice2005(Topology and Confinement), Dublin, July 25-30, 2005. v2: reference adde

Wage subsidies and international trade: when does policy coordination pay?

National labour market institutions interact across national boundaries when product markets are global. Labour market policies can thus entail spill-overs, a fact widely ignored in the academic literature. This paper studies the effects of wage subsidies in an international duopoly model with unionised labour markets. We document both positive and negative spill-over effects and discuss the benefits and costs from international policy coordination both for the case of symmetric and asymmetric labour market institutions. Our results suggest that institutional differences could sign responsible for the slow speed at which labour market policy coordination has progressed so far

Analytic structure of the Landau gauge gluon propagator

The analytic structure of the non-perturbative gluon propagator contains information on the absence of gluons from the physical spectrum of the theory. We study this structure from numerical solutions in the complex momentum plane of the gluon and ghost Dyson-Schwinger equations in Landau gauge Yang-Mills theory. The resulting ghost and gluon propagators are analytic apart from a distinct cut structure on the real, timelike momentum axis. The propagator violates the Osterwalder-Schrader positivity condition, confirming the absence of gluons from the asymptotic spectrum of the theory.Comment: 5 pages, 7 figure

Perturbation Theory by Flow Equations: Dimerized and Frustrated S=1/2 Chain

The flow equation method (Wegner 1994) is used as continuous unitary transformation to construct perturbatively effective Hamiltonians. The method is illustrated in detail for dimerized and frustrated antiferromagnetic S=1/2 chains. The effective Hamiltonians conserve the number of elementary excitations which are S=1 magnons for the dimerized chains. The sectors of different number of excitations are clearly separated. Easy-to-use results for the gap, the dispersion and the ground state energies of the chains are provided.Comment: 18 pages, 15 figures included, to appear in Eur. Phys. J. B; Electronic data will be made available on appearance of articl