The chiral phase transition for lattice QCD with 2 color-sextet quarks

Journal Article · Mon Sep 21 00:00:00 EDT 2015 · Physical Review. D, Particles, Fields, Gravitation and Cosmology

DOI:https://doi.org/10.1103/PhysRevD.92.054508· OSTI ID:1542094

Kogut, J. B. ^[1]; Sinclair, D. K. ^[2]

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1. Dept. of Energy, Washington, D.C. (United States). Div. of High Energy Physics; Univ. of Maryland, College Park, MD (United States). Dept. of Physics, TQHN
2. Argonne National Lab. (ANL), Argonne, IL (United States). HEP Div.

QCD with 2 flavors of massless color-sextet quarks is studied as a possible walking-Technicolor candidate. We simulate the lattice version of this model at finite temperatures near to the chiral-symmetry restoration transition, to determine whether it is indeed a walking theory (QCD-like with a running coupling which evolves slowly over an appreciable range of length scales) or if it has an infrared fixed point, making it a conformal field theory. The lattice spacing at this transition is decreased towards zero by increasing the number N_t of lattice sites in the temporal direction. Our simulations are performed at N_t = 4,6,8,12, on lattices with spatial extent much larger than the temporal extent. A range of small fermion masses is chosen to make predictions for the chiral (zero mass) limit. We find that the bare lattice coupling does decrease as the lattice spacing is decreased. However, it decreases more slowly than would be predicted by asymptotic freedom. We discuss whether this means that the coupling is approaching a finite value as lattice N_t is increased—the conformal option, or if the apparent disagreement with the scaling predicted by asymptotic freedom is because the lattice coupling is a poor expansion parameter, and the theory walks. Currently, evidence favors QCD with 2 color-sextet quarks being a conformal field theory. Other potential sources of disagreement with the walking hypothesis are also discussed. In conclusion, we also report an estimate of the position of the deconfinement transition for N_t = 12, needed for choosing parameters for zero-temperature simulations.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-06CH11357; AC02-05CH11231; TG-MCA99S015
• OSTI ID: 1542094
• Alternate ID(s): OSTI ID: 1222366
• Journal Information: Physical Review. D, Particles, Fields, Gravitation and Cosmology, Vol. 92, Issue 5; ISSN 1550-7998
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

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