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Register a new userThe conformal window on the lattice
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Authors
Luigi Del Debbio
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Lattice simulations can play an important role in the study of dynamical electroweak symmetry breaking by providing quantitative results on the nonperturbative dynamics of candidate theories. For this programme to succeed, it is crucial to identify the questions that are relevant for phenomenology, and develop the tools that will provide robust answers to these questions. The existence of a conformal window for nonsupersymmetric gauge theories, and its characterization, is one of the phenomenologically important problems that can be studied on the lattice. We summarize the recent results from studies of IR fixed points by numerical simulations, discuss their current limitations, and analyze the future perspectives.
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We study the SU(3) gauge theory with twelve flavours of fermions in the fundamental representation as a prototype of non-Abelian gauge theories inside the conformal window. Guided by the pattern of underlying symmetries, chiral and conformal, we analyze the two-point functions theoretically and on the lattice, and determine the finite size scaling and the infinite volume fermion mass dependence of the would-be hadron masses. We show that the spectrum in the Coulomb phase of the system can be described in the context of a universal scaling analysis and we provide the nonperturbative determination of the fermion mass anomalous dimension gamma*=0.235(46) at the infrared fixed point. We comment on the agreement with the four-loop perturbative prediction for this quantity and we provide a unified description of all existing lattice results for the spectrum of this system, them being in the Coulomb phase or the asymptotically free phase. Our results corroborate the view that the fixed point we are studying is not associated to a physical singularity along the bare coupling line and estimates of physical observables can be attempted on either side of the fixed point. Finally, we observe the restoration of the U(1) axial symmetry in the two-point functions.
We report on the spectrum of the SU(3) gauge theory with twelve flavours in the fundamental representation of the gauge group. We isolate distinctive features of the hadronic phase - the one proper of QCD at zero temperature - and the so called conformal phase. The latter should emerge at sufficiently large Nf and before the loss of asymptotic freedom. In particular, we analyse available lattice data for the spectrum of Nf=12 and include a comparison with results with Nf=16; the latter theory, predicted by the perturbative beta-function to develop an IRFP and therefore be in the conformal phase, can serve as a paradigm for the study of theories in the conformal window. Our analysis suggests that the theory with twelve flavours is in the conformal window, possibly close to its lower boundary.
Results are reported for the beta-function of weakly coupled conformal gauge theories on the lattice, SU(3) with Nf=14 fundamental and Nf=3 sextet fermions. The models are chosen to be close to the upper end of the conformal window where perturbation theory is reliable hence a fixed point is expected. The study serves as a test of how well lattice methods perform in the weakly coupled conformal cases. We also comment on the 5-loop beta-function of two models close to the lower end of the conformal window, SU(3) with Nf=12 fundamental and Nf=2 sextet fermions.
Using the superconformal (SC) indices techniques, we construct Seiberg type dualities for $mathcal{N}=1$ supersymmetric field theories outside the conformal windows. These theories are physically distinguished by the presence of chiral superfields with small or negative $R$-charges.
We propose a novel constraint on the gauge dynamics of strongly interacting gauge theories stemming from the a theorem. The inequality we suggest is used to provide a lower bound on the conformal window of four dimensional gauge theories.
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