Statut  Confirmé 
Série  IPNX 
Domaines  hepph 
Date  Jeudi 23 Novembre 2017 
Heure  11:00 
Institut  CPHT 
Salle  Salle de conférences, bât. 6 
Nom de l'orateur  Pelaez 
Prenom de l'orateur  Marcela 
Addresse email de l'orateur  
Institution de l'orateur  Republica U., Montevideo 
Titre  Small parameters in infrared QCD 
Résumé  Lattice simulations show that the running coupling constants obtained through QCD vertices differ in the infrared even though their bare values coincide. For instance, at low momenta the strength of the quarkgluon coupling is about twice the ghostgluon coupling. None of them diverge in the infrared as it is predicted by standard perturbation theory. Moreover, the ghostgluon coupling remains moderate even in the infrared. This observation motivates the use of perturbation theory in the ghostgluon sector in the frame of a massive deformation of QCD Lagrangian in Landau gauge. However, perturbation theory in the quark sector within this massive Lagrangian doesn´t bring as good results as in the pure YangMills case, as should be expected from the larger value of the quarkgluon coupling constant. We propose a controlled systematic expansion in full QCD based in two small parameters: first the Yang.Mills sector couplings and second the inverse of the number of colors (largeNc limit). The second approximation relies on the fact that the general features of QCD can be observed in the largeNc limit. This systematic expansion allows us to properly introduced the use of the renormalization group for the rainbow resummation. At leading order, this double expansion leads to the wellknown rainbow approximation for the quark propagator whose solution shows spontaneous chiral symmetry breaking for sufficiently large quarkgluon coupling constant. 
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