TY - JOUR

T1 - Twelve massless flavors and three colors below the conformal window

AU - Fodor, Zoltán

AU - Holland, Kieran

AU - Kuti, Julius

AU - Nógrádi, Dániel

AU - Schroeder, Chris

N1 - Funding Information:
The simulations were performed using computational resources at Fermilab and JLab, under the auspices of USQCD and SciDAC, from the Teragrid structure and at Wuppertal. We are grateful to Kalman Szabo, Sandor Katz, and Stefan Krieg for helping us in using the Wuppertal RHMC code. Simulation on GPU clusters were facilitated by the CUDA ports of [72] . This research is supported by the NSF under grants 0704171 and 0970137 , by the DOE under grants DOE-FG03-97ER40546 , DOE-FG-02-97ER25308 , by the DFG under grant FO 502/1 and by SFB-TR/55 , and the EU Framework Programme 7 grant (FP7/2007-2013)/ERC No 208740 . D.N. would like to thank the Aspen Center for Physics for invitation to the 2010 BSM summer program. C.R.S. is indebted to the Theory Group at CERN for hospitality at the LGT 2010 workshop.

PY - 2011/9/14

Y1 - 2011/9/14

N2 - We report new results for a frequently discussed gauge theory with twelve fermion flavors in the fundamental representation of the SU(3) color gauge group. The model, controversial with respect to its conformality, is important in non-perturbative studies searching for a viable composite Higgs mechanism beyond the Standard Model (BSM). In comparison with earlier work, our new simulations apply larger volumes and probe deeper in fermion and pion masses toward the chiral limit. Investigating the controversy, we subject the model to opposite hypotheses with respect to the conformal window. In the first hypothesis, below the conformal window, we test chiral symmetry breaking (χSB) with its Goldstone spectrum, Fπ, the χSB condensate, and several composite hadron states as analytic functions of the fermion mass when varied in a limited range with our best effort to control finite volume effects. In the second test, for the alternate hypothesis inside the conformal window, we probe conformal behavior driven by a single anomalous mass dimension under the assumption of unbroken chiral symmetry at vanishing fermion mass. Our results at fixed gauge coupling, based on the assumptions of the two hypotheses we define, show low level of confidence in the conformal scenario with leading order scaling analysis. Relaxing the important assumption of leading mass-deformed conformality with its conformal finite size scaling would require added theoretical understanding of the scaling violation terms in the conformal analysis and a comprehensive test of its effects on the confidence level of the fits. Results for the running coupling, based on the force between static sources, and preliminary indications for the finite temperature transition are also presented. Staggered lattice fermions with stout-suppressed taste breaking are used throughout the simulations.

AB - We report new results for a frequently discussed gauge theory with twelve fermion flavors in the fundamental representation of the SU(3) color gauge group. The model, controversial with respect to its conformality, is important in non-perturbative studies searching for a viable composite Higgs mechanism beyond the Standard Model (BSM). In comparison with earlier work, our new simulations apply larger volumes and probe deeper in fermion and pion masses toward the chiral limit. Investigating the controversy, we subject the model to opposite hypotheses with respect to the conformal window. In the first hypothesis, below the conformal window, we test chiral symmetry breaking (χSB) with its Goldstone spectrum, Fπ, the χSB condensate, and several composite hadron states as analytic functions of the fermion mass when varied in a limited range with our best effort to control finite volume effects. In the second test, for the alternate hypothesis inside the conformal window, we probe conformal behavior driven by a single anomalous mass dimension under the assumption of unbroken chiral symmetry at vanishing fermion mass. Our results at fixed gauge coupling, based on the assumptions of the two hypotheses we define, show low level of confidence in the conformal scenario with leading order scaling analysis. Relaxing the important assumption of leading mass-deformed conformality with its conformal finite size scaling would require added theoretical understanding of the scaling violation terms in the conformal analysis and a comprehensive test of its effects on the confidence level of the fits. Results for the running coupling, based on the force between static sources, and preliminary indications for the finite temperature transition are also presented. Staggered lattice fermions with stout-suppressed taste breaking are used throughout the simulations.

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U2 - 10.1016/j.physletb.2011.07.037

DO - 10.1016/j.physletb.2011.07.037

M3 - Article

AN - SCOPUS:80052265442

VL - 703

SP - 348

EP - 358

JO - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

JF - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

SN - 0370-2693

IS - 3

ER -