36,654 research outputs found
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
On critical scaling at the QCD N_f=2 chiral phase transition
We investigate the critical scaling of the quark propagator of N_f=2 QCD
close to the chiral phase transition at finite temperature. We argue that it is
mandatory to take into account the back-reaction effects of pions and the sigma
onto the quark to observe critical behavior beyond mean field. On condition of
self-consistency of the quark Dyson-Schwinger equation we extract the scaling
behavior for the quark propagator analytically. Crucial in this respect is the
correct pion dispersion relation when the critical temperature is approached
from below. Our results are consistent with the known relations for the quark
condensate and the pion decay constant from universality. We verify the
analytical findings also numerically assuming the critical dispersion relation
for the Goldstone bosons.Comment: 9 pages, 6 figure
Chiral and deconfinement phase transitions of two-flavour QCD at finite temperature and chemical potential
We present results for the chiral and deconfinement transition of two flavor
QCD at finite temperature and chemical potential. To this end we study the
quark condensate and its dual, the dressed Polyakov loop, with functional
methods using a set of Dyson-Schwinger equations. The quark-propagator is
determined self-consistently within a truncation scheme including temperature
and in-medium effects of the gluon propagator. For the chiral transition we
find a crossover turning into a first order transition at a critical endpoint
at large quark chemical potential, . For the
deconfinement transition we find a pseudo-critical temperature above the chiral
transition in the crossover region but coinciding transition temperatures close
to the critical endpoint.Comment: 4 pages, 4 figures. v2: minor changes, comments adde
The Logic & Limits of the Exceptional Circumstances Test in Magill and IMS Health
In this Article, we show that, in contrast to the Commission\u27s balancing approach in Microsoft, the ECJ\u27s narrow construction of the obligation to license IP under Article 82 of the EC Treaty is based on sound economics and constitutes appropriate public policy. The set of âexceptional circumstancesâ listed in Magill and IMS Health constitutes a reasonable implementation of the optimal legal standard for the assessment of refusals to licence IP: modified per se legality. In the IP context, an obligation to make property available is a requirement for compulsory licensing. The ECJ test limits compulsory licensing to those situations in which the prospective social benefits of licensing are large, while the negative effects of reducing the incentives to innovate are small. The ECJ test ensures that intervention is restricted to cases where the intervention is still likely to increase social welfare. The Commission\u27s test in Microsoft, being a balancing test, does not. As noted by Professor Gerardin, âbalancing ex ante vs. ex post efficiencies is obviously a very difficult process, which even the most sophisticated economists may find daunting. The risk of mistaken decisions is therefore high.
Quark spectral properties above Tc from Dyson-Schwinger equations
We report on an analysis of the quark spectral representation at finite
temperatures based on the quark propagator determined from its Dyson-Schwinger
equation in Landau gauge. In Euclidean space we achieve nice agreement with
recent results from quenched lattice QCD. We find different analytical
properties of the quark propagator below and above the deconfinement
transition. Using a variety of ansaetze for the spectral function we then
analyze the possible quasiparticle spectrum, in particular its quark mass and
momentum dependence in the high temperature phase. This analysis is completed
by an application of the Maximum Entropy Method, in principle allowing for any
positive semi-definite spectral function. Our results motivate a more direct
determination of the spectral function in the framework of Dyson-Schwinger
equations
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