9,517 research outputs found

    Toward the Global Structure of Conformal Theories in the SU(3) Gauge Theory

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    We introduce a new concept "conformal theories with an IR cutoff", after pointing out that the following two categories in SU(3) gauge theories with fundamental N_f fermions possess an IR fixed point: Large N_f QCD with N_f in the conformal window (referred as Conformal QCD) and small N_f QCD with N_f out of the conformal window at temperature T/Tc > 1 (referred as High Temperature QCD). In the conformal theories with an IR cutoff there exists the "conformal region'" together with the confining region and the deconfining region. We verify numerically on a lattice of the size 16^3 x64 the existence of the conformal region and the non-trivial Z(3) structure of the vacuum and the Yukawa-type decay form of meson propagators in the conformal region. We stress that High Temperature QCD is intrinsically accompanied with an IR cutoff. Therefore the understanding the vacuum structure and the property of correlation functions is the key to resolve long standing issues in High Temperature QCD. We further argue that there is a precise correspondence between Conformal QCD and High Temperature QCD in the temporal propagators under the change of the parameters N_f and T/T_c respectively: the one boundary is close to meson states and the other is close to free quark states. In particular, we find the correspondence between Conformal QCD with N_f = 7 and High Temperature QCD with N_f=2 at T ~ 2 Tc being in close relation to a meson unparticle model. From this we estimate the anomalous mass dimension gamma* = 1.2 (1) for N_f=7.Comment: 7 pages, 5 figures, based on the work in collaboration with K. -I Ishikawa, Yu Nakayama and T. Yoshie, presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German

    Computers for Lattice Field Theories

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    Parallel computers dedicated to lattice field theories are reviewed with emphasis on the three recent projects, the Teraflops project in the US, the CP-PACS project in Japan and the 0.5-Teraflops project in the US. Some new commercial parallel computers are also discussed. Recent development of semiconductor technologies is briefly surveyed in relation to possible approaches toward Teraflops computers.Comment: 15 pages with 16 PS figures, review presented at Lattice 93, LaTeX (espcrc2.sty required

    Chiral Phase Transition in Lattice QCD with Wilson Quarks

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    The nature of the chiral phase transition in lattice QCD is studied for the cases of 2, 3 and 6 flavors with degenerate Wilson quarks, mainly on a lattice with the temporal direction extension Nt=4N_t=4. We find that the chiral phase transition is continuous for the case of 2 flavors, while it is of first order for 3 and 6 flavors.Comment: uuencoded compressed tar file, LaTeX, 14 pages, 7 figure

    Non-equilibrium and non-linear stationary state in thermoelectric materials

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    Efficiency of thermoelectric materials is characterized by the figure of merit Z. Z has been believed to be a peculiar material constant. However, the accurate measurements in the present work reveal that Z has large size dependence and a non-linear temperature distribution appears as stationary state in the thermoelectric material. The observation of these phenomena is achieved by the Harman method. This method is the most appropriate way to investigate the thermoelectric properties because the dc and ac resistances are measured by the same electrode configuration. We describe the anomalous thermoelectric properties observed in mainly (Bi,Sb)2Te3 by the Harman method and then insist that Z is not the peculiar material constant but must be defined as the physical quantity dependent of the size and the position in the material.Comment: 9 pages, 4 figures. submitted to Applied Physics Lette

    QCD Phase Transition with Strange Quark in Wilson Formalism for Fermions

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    The nature of QCD phase transition is studied with massless up and down quarks and a light strange quark, using the Wilson formalism for quarks on a lattice with the temporal direction extension Nt=4N_t=4. We find that the phase transition is first order in the cases of both about 150 MeV and 400 MeV for the strange quark mass. These results together with those for three degenerate quarks suggest that QCD phase transition in nature is first order.Comment: uuencoded compressed tar file, LaTeX, 13 pages, 9 figures, Minor errors for quoting references are corrected and a reference is adde

    Phase Diagram of QCD at Finite Temperatures with Wilson Fermions

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    Phase diagram of QCD with Wilson fermions for various numbers of flavors NFN_F is discussed. Our simulations mainly performed on a lattice with the temporal size Nt=4N_t =4 indicate the following: The chiral phase transition is of first order when 3≤NF≤63 \le N_F \le 6, while it is continuous when NF=2N_F=2. For the realistic case of massless u and d quarks and the strange quark with mq=150m_q = 150 MeV, the phase transition is first order. The sharp transition in the intermediate mass region for NF=2N_F=2 at Nt=4N_t=4 observed by the MILC group disappears when an RG improvement is made for the pure gauge action.Comment: ps file, 7 pages with 5 figures, contribution to Lattice 94
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