# Rencontre de Physique des Particules 2015

15-16 janvier 2015
Institut Henri Poincaré
Fuseau horaire Europe/Paris

## Renormalization Group Optimized Perturbation: some illustrations at zero and finite temperature.

16 janv. 2015 à 16:50
15m
Chair: Bira Van Kolck, Amphi Hermite (Institut Henri Poincaré)

### Chair: Bira Van Kolck, Amphi Hermite

#### Institut Henri Poincaré

11, rue Pierre et Marie Curie 75005 Paris

### Orateur

Jean-Loic Kneur (LCC Montpellier)

### Description

We discuss our recently developed variant of the so-called optimized perturbation (OPT), 'RGOPT', consistently resumming renormalization group dependence generically for zero or finite temperature theories. It is illustrated with a rather precise determination of 1) the QCD basic scale and coupling from the pion decay constant $F_\pi$: $\alpha_S(m_Z)[\overline{MS}] \simeq 0.1174 \pm 0.002$; 2) the quark condensate $<\bar q q>$ in the chiral limit. 3) At finite temperature the pressure for the illustrative $\phi^4$ model is calculated to second (modified perturbation) order. Our method and results differ sharply from other similar resummation approaches, in particular the notoriously bad stability and scale dependence of thermal perturbative expansions for moderately large coupling is shown to drastically improve, with anticipated similar properties in thermal QCD.

### Summary

We discuss our recently developed variant of the so-called optimized perturbation (OPT), 'RGOPT', consistently resumming renormalization group dependence generically for zero or finite temperature theories. It is illustrated with a rather precise determination of 1) the QCD basic scale and coupling from the pion decay constant $F_\pi$: $\alpha_S(m_Z)[\overline{MS}] \simeq 0.1174 \pm 0.002$;
2) the quark condensate $<\bar q q>$ in the chiral limit.
3) At finite temperature the pressure for the illustrative $\phi^4$ model is calculated to second (modified perturbation) order.
Our method and results differ sharply from other similar resummation approaches, in particular the notoriously bad stability and scale dependence of thermal perturbative expansions for moderately large coupling is shown to drastically improve, with anticipated similar properties in thermal QCD.

### Auteur principal

Jean-Loic Kneur (LCC Montpellier)

### Documents de présentation

 Transparents
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