2,587 research outputs found

    Low energy spectral and scattering theory for relativistic Schroedinger operators

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    Spectral and scattering theory at low energy for the relativistic Schroedinger operator are investigated. Some striking properties at thresholds of this operator are exhibited, as for example the absence of 0-energy resonance. Low energy behavior of the wave operators and of the scattering operator are studied, and stationary expressions in terms of generalized eigenfunctions are proved for the former operators. Under slightly stronger conditions on the perturbation the absolute continuity of the spectrum on the positive semi axis is demonstrated. Finally, an explicit formula for the action of the free evolution group is derived. Such a formula, which is well known in the usual Schroedinger case, was apparently not available in the relativistic setting.Comment: 27 page

    Thermodynamics of (2+1)-flavor QCD

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    We report on the status of our QCD thermodynamics project. It is performed on the QCDOC machine at Brookhaven National Laboratory and the APEnext machine at Bielefeld University. Using a 2+1 flavor formulation of QCD at almost realistic quark masses we calculated several thermodynamical quantities. In this proceeding we show the susceptibilites of the chiral condensate and the Polyakov loop, the static quark potential and the spatial string tension.Comment: To appear in the proceedings of International Conference on Strong and Electroweak Matter (SEWM 2006), Upton, New York, 10-13 May 200

    Equation of state in 2+1 flavor QCD with improved Wilson quarks by the fixed scale approach

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    We study the equation of state in 2+1 flavor QCD with nonperturbatively improved Wilson quarks coupled with the RG-improved Iwasaki glue. We apply the TT-integration method to nonperturbatively calculate the equation of state by the fixed-scale approach. With the fixed-scale approach, we can purely vary the temperature on a line of constant physics without changing the system size and renormalization constants. Unlike the conventional fixed-NtN_t approach, it is easy to keep scaling violations small at low temperature in the fixed scale approach. We study 2+1 flavor QCD at light quark mass corresponding to mπ/mρ0.63m_\pi/m_\rho \simeq 0.63, while the strange quark mass is chosen around the physical point. Although the light quark masses are heavier than the physical values yet, our equation of state is roughly consistent with recent results with highly improved staggered quarks at large NtN_t.Comment: 14 pages, 12 figures, v2: Table I and Figure 3 are corrected, reference updated. Main discussions and conclusions are unchanged, v3: version to appear in PRD, v4: reference adde

    Lattice QCD Study of the Pentaquark Baryons

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    We study the spin 12\frac12 hadronic state in quenched lattice QCD to search for a possible S=+1S=+1 pentaquark resonance. Simulations are carried out on 83×248^3\times 24, 103×2410^3\times 24, 123×2412^3\times 24 and 163×2416^3\times 24 lattices at β\beta=5.7 at the quenched level with the standard plaquette gauge action and Wilson quark action. We adopt two independent operators with I=0 and JP=12J^P=\frac12 to construct a 2×22\times 2 correlation matrix. After the diagonalization of the correlation matrix, we successfully obtain the energies of the ground-state and the 1st excited-state in this channel. The volume dependence of the energies suggests the existence of a possible resonance state slightly above the NK threshold in I=0 and JP=12J^P=\frac12^- channel.Comment: Talk given at the International Workshop on PENTAQUARK04, SPring-8, Japan, 20-23 July 2004; 7 pages, 3 figure

    Zero mode contribution in quarkonium correlators and in-medium properties of heavy quarks

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    We calculate the low energy contribution to quarkonium correlators in Euclidean time in lattice QCD. This contribution was found to give the dominant source of the temperature dependence of the correlators. We have found that the low energy contribution is well described by a quasi-particle model and have determined the effective temperature dependent heavy quark mass.Comment: Contribution to QM2008, 4 pages, LaTeX, uses iopart.cls, corrected typo
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