Browsing by Subject "1/N Expansion"

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  • Bigazzi, Francesco; Cotrone, Aldo L.; Järvinen, Matti; Kiritsis, Elias (2020)
    Among the possible CP-odd couplings of the axion to ordinary matter, the most relevant ones for phenomenology are the Yukawa couplings to nucleons. We analyze such non-derivative couplings within three different approaches: standard effective field theory, the Skyrme model and holographic QCD. In all the cases, the couplings can be related to the CP-odd non-derivative couplings to nucleons of the low-lying mesons and the eta '. Using the effective field theory approach we discuss how to derive the expressions for the CP-odd interaction terms as functions of the parameters of the effective Lagrangian at generic number of colors N-c and flavors N-f. Then, we compute the CP-odd couplings to nucleons of the axion, the eta ' and the pseudo-Goldstone mesons in both the Skyrme and the holographic QCD model with N-f = 2, 3. We present model-independent expressions for the coefficients of the non-derivative axion-nucleon couplings. This allows us to provide quantitative estimates of these couplings.
  • Ryttov, Thomas A.; Tuominen, Kimmo (2019)
    We consider a non-Abelian gauge theory with N-f fermions and discuss the possible existence of a non-trivial UV fixed point at large N-f . Specifically, we study the anomalous dimension of the (rescaled) glueball operator Tr F-2 to first order in 1/N-f by relating it to the derivative of the beta function at the fixed point. At the fixed point the anomalous dimension violates its unitarity bound and so the (rescaled) glueball operator is either decoupled or the fixed point does not exist. We also study the anomalous dimensions of the two spin-1/2 baryon operators to first order in 1/N-f for an SU(3) gauge theory with fundamental fermions and find them to be relatively small and well within their associated unitarity bounds.