Theory Seminar: Low-energy effective action for pions and a dilatonic meson

Friday, 10 June 2016 from 12:00 to 13:00 (Europe/Madrid) at IFAE ( IFAE Seminar room )

Speaker: Maarten Golterman (San Francisco State University)


Abstract:
Numerical simulations of QCD-like theories in which the number of flavors is adjusted so that the beta function is very small, but confinement and chiral symmetry breaking nevertheless take place, appear to reveal the presence of a flavor-singlet scalar meson which can be as light as the pions. Because the breaking of dilatation symmetry, quantified by the beta function, is small relative to QCD, a possible explanation is that the scalar meson is a pseudo Nambu-Goldstone boson associated with the approximate dilatation symmetry. We use this observation to systematically develop a low-energy effective action that accounts for both the pions and the “dilatonic” scalar meson. In order to justify the power counting that controls the couplings of the dilatonic meson we invoke the Veneziano limit, in which the number of fundamental- representation flavors Nf grows in proportion with the number of colors Nc, while the ratio Nf/Nc is kept close to, but below, the critical value where the conformal window is entered.

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