We study Quantum Chromodynamics with eight flavours by use of lattice simulations and present evidence that the theory still breaks chiral symmetry in the zero temperature, continuum limit. This confirms that the lower end of the conformal window of QCD lies above Nf = 8.Comment: 19 pages, 7 figures; added a number of relevant references and comments to introduction, enhanced captions for figures 6 and 7, corrected typos and minor lapses of styl

We discuss the existence of a conformal phase in SUðNÞ gauge theories in four dimensions. In this lattice study, we explore the model in the bare parameter space, varying the lattice coupling and bare mass. Simulations are carried out with three colors and 12 flavors of dynamical staggered fermions in the fundamental representation. The analysis of the chiral order parameter and the mass spectrum of the theory indicates the restoration of chiral symmetry at zero temperature and the presence of a Coulomb-like phase, depicting a scenario compatible with the existence of an infrared stable fixed point at nonzero coupling. Our analysis supports the conclusion that the onset of the conformal window for QCD-like theories is smaller than N f ¼ 12, before the loss of asymptotic freedom at 16 and 1/2 flavors. We discuss open questions and future directions.

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We study the temperature dependence of bottomonium for temperatures in the range 0.4Tc < T < 2.1Tc, using nonrelativistic dynamics for the bottom quark and full relativistic lattice QCD simulations for N f = 2 light flavors on a highly anisotropic lattice. We find that the Υ is insensitive to the temperature in this range, while the χ b propagators show a crossover from the exponential decay characterizing the hadronic phase to a power-law behaviour consistent with nearly-free dynamics at T ≃ 2Tc.

We present results on the bottomonium spectrum at temperatures above and below the deconfinement crossover temperature, T c , from dynamical lattice QCD simulations. The heavy quark is treated with a non-relativistic effective field theory on the lattice and serves as a probe of the hot medium. Ensembles with a finer spatial lattice spacing and a greater range of temperatures below T c than those previously employed by this collaboration are used. In addition, there are N f = 2 + 1 flavours of Wilson clover quark in the sea with M π ≈ 400 MeV and we perform a more careful tuning of the bottom quark mass in this work. We calculate the spectral functions of S and P wave bottomonium states using the maximum entropy method and confirm earlier findings on the survival of the ground state S wave states up to at least 2T c and the immediate dissociation of the P wave states above T c .