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A. Ipp:
"Scalar theory pressure beyond the local potential approximation";
Talk: Yukawa International Molecule Workshop, Yukawa Institute for Theoretical Physics (invited); 2011-08-22 - 2011-09-09.

Strict perturbation theory of a scalar theory at finite temperature
exhibits the same poor convergence properties as QCD or QED, already at
moderately large couplings. It is therefore an ideal test bed to
implement improved convergence schemes like improved calculations using
the Non-Perturbative Renormalization Group (NPRG).

In this talk I want to present results beyond the already successful
Local Potential Approximation (LPA). We apply an improved scheme that
has been developed by Blaizot, Mendez-Galain, and Wschebor (BMW). This
scheme permits a good determination of the momentum dependence of the
n-point functions at zero temperature. Applied to finite temperature,
one can expect this method to capture accurately the contributions to
the thermodynamical functions of thermal fluctuations from various
momentum ranges. This scheme involves also non trivial momentum
dependent self-energies. We find that results obtained with this new
scheme are not too different from those of the LPA. This suggests that
the LPA may already capture the main contribution to the exact pressure.
This agreement persists up to the largest couplings, where strict
perturbation theory fails miserably. This may also hint to the validity
of the quasiparticle picture of such a system.