Charmonia above the Deconfinement Phase Transition

Analyzing correlation functions of charmonia at finite temperature ($T$) on $32^3\times(32-96)$ anisotropic lattices by the maximum entropy method (MEM), we find that $J/\psi$ and $\eta_c$ survive as distinct resonances in the plasma even up to $T \simeq 1.6 T_c$ and that they eventually dissociate between $1.6 T_c$ and $1.9 T_c$ ($T_c$ is the critical temperature of deconfinement). This suggests that the deconfined plasma is non-perturbative enough to hold heavy-quark bound states. The importance of having sufficient number of temporal data points in the MEM analysis is also emphasized.Comment: Lattice2003(nonzero), 3 pages, 3 figure

Excited D-branes and Supergravity Solutions

We investigate the general solution with the symmetry ISO(1,p)xSO(9-p) of Type II supergravity (the three-parameter solution) from the viewpoint of the superstring theory. We find that one of the three parameters (c_1) is closely related to the ``dilaton charge'' and the appearance of the dilaton charge is a consequence of deformations of the boundary condition from that of the boundary state for BPS D-branes. We give three examples of the deformed D-branes by considering the tachyon condensation from systems of D-\bar{D}p-branes, unstable D9-branes and unstable D-instantons to the BPS saturated Dp-branes, respectively. We argue that the deformed systems are generally regarded as tachyonic and/or massive excitations of the open strings on Dp-\bar{D}p-brane systems.Comment: 29 pages, 6 figures, LaTeX2e, typos corrected, references adde

Hadronic Spectral Functions above the QCD Phase Transition

We extract the spectral functions in the scalar, pseudo-scalar, vector, and axial vector channels above the deconfinement phase transition temperature (Tc) using the maximum entropy method (MEM). We use anisotropic lattices, 32^3 * 32, 40, 54, 72, 80, and 96 (corresponding to T = 2.3 Tc --> 0.8 Tc), with the renormalized anisotropy xi = 4.0 to have enough temporal data points to carry out the MEM analysis. Our result suggests that the spectral functions continue to possess non-trivial structures even above Tc and in addition that there is a qualitative change in the state of the deconfined matter between 1.5 Tc and 2 Tc.Comment: 3 pages, 4 figures, Lattice2002(nonzerot

Exact description of D-branes in K-matrix theory

We summarize how to describe D-branes in a matrix theory based on unstable D-instantons, which we call K-matrix theory, and explicity show that D-branes can be constructed as bound states of infinitly many unstable D-instantons. We examine the fluctuations around Dp-brane solutions in the matrix theory and show that they correctly reproduce fields on the Dp-brane world-volume. Plugging them into the action of the matrix theory, we precisely obtain the Dp-brane action as the effective action of the fluctuations.Comment: 19 pages, Talk given by S.S. at the 17th Nishinomiya-Yukawa Memorial Symposium, Nishinomiya, November, 200

Maximum Entropy Analysis of the Spectral Functions in Lattice QCD

First principle calculation of the QCD spectral functions (SPFs) based on the lattice QCD simulations is reviewed. Special emphasis is placed on the Bayesian inference theory and the Maximum Entropy Method (MEM), which is a useful tool to extract SPFs from the imaginary-time correlation functions numerically obtained by the Monte Carlo method. Three important aspects of MEM are (i) it does not require a priori assumptions or parametrizations of SPFs, (ii) for given data, a unique solution is obtained if it exists, and (iii) the statistical significance of the solution can be quantitatively analyzed. The ability of MEM is explicitly demonstrated by using mock data as well as lattice QCD data. When applied to lattice data, MEM correctly reproduces the low-energy resonances and shows the existence of high-energy continuum in hadronic correlation functions. This opens up various possibilities for studying hadronic properties in QCD beyond the conventional way of analyzing the lattice data. Future problems to be studied by MEM in lattice QCD are also summarized.Comment: 51 pages, 17 figures, typos corrected, discussions on the boundary conditions and renormalization constants added. To appear in Progress in Particle and Nuclear Physics, Vol.4

Cutoff effects in meson spectral functions

We study the lattice spacing dependence of meson spectral functions calculated in quenched QCD with domain wall fermions as well as clover Wilson fermions in quenched and partially-quenched QCD. We conclude that for lattice spacing $a \le 3$ GeV all excited states appearing in the spectral functions are lattice artifacts.Comment: Lattice 2004 (non-zero), 3 pages, 3 figures, uses espcrc2 packag

Back-to-Back Correlations for Bosons Modified by Medium

Novel back-to-back correlations are shown to arise for thermal ensembles of squeezed bosonic states associated with medium-modified mass-shifts. The strength of these correlations could become unexpectedly large in heavy ion collisions.Comment: Talk given at Quark Matter 99, Torino, Italy, May 10-15, 1999. LaTeX, 4 pages, 2 eps figures. To appear in Nucl. Phys.

J/ψJ/\psi and ηc\eta_c in the Deconfined Plasma from Lattice QCD

Analyzing correlation functions of charmonia at finite temperature ($T$) on $32^3\times(32-96)$ anisotropic lattices by the maximum entropy method (MEM), we find that $J/\psi$ and $\eta_c$ survive as distinct resonances in the plasma even up to $T \simeq 1.6 T_c$ and that they eventually dissociate between $1.6 T_c$ and $1.9 T_c$ ($T_c$ is the critical temperature of deconfinement). This suggests that the deconfined plasma is non-perturbative enough to hold heavy-quark bound states. The importance of having sufficient number of temporal data points in MEM analyses is also emphasized.Comment: 4 pages, 4 figures, REVTEX, version to appear in Physical Review Letter