Free Meson Spectral Functions on the Lattice

We present results from an analytic calculation of thermal meson spectral functions in the infinite temperature (free field) limit. We compare spectral functions for various lattice fermion formulations used at present in studies of in-medium properties of hadrons based on the maximum entropy method (MEM). In particular, we will present a new calculation of spectral functions performed with extended quark sources.Comment: 3 pages, Lattice2003(nonzero

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

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

Charged Higgs Production in Association with W Boson at Photon Colliders

It is important to explore the Higgs sector in order to identify the model beyond the standard model. We study the charged Higgs production in the $\gamma\gamma$ mode of a linear collider (LC) with 1000 GeV center of mass energy. We show that the cross sections for the $\gamma \gamma \to H^\pm W^\mp$ processes can be significantly enhanced in the two Higgs doublet model (THDM). The cross section can reach 0.1 - 100 fb which is comparable to other charged Higgs boson production processes at a photon collider. While for other processes the cross sections are too small for $m_H^\pm \geq 500$ GeV, $0.1 - 100$ fb can be expected in the $\gamma\gamma \to H^\pm W^\mp$ processes for $m_H^\pm \geq 570$ GeV when $m_{A^0}=800$ GeV. Therefore, even if the charged Higgs bosons can not be detected at the Large Hadron Collider (LHC), and even if the charged Higgs bosons are too heavy to be detected in other charged Higgs boson production processes at the LC, it may be possible to detect them in this process.Comment: To appear in the proceedings of 2005 International Linear Collider Workshop (LCWS 2005), Stanford, California, 18-22 Mar 200

Charmonium at finite temperature

We study charmoinum correlators and spectral functions at finite temperature within the quenched approximation using isotropic lattices with lattice spacing a^-1=4.86 GeV and 9.72 GeV. Although we observe some medium modifications of the ground state charmonium spectral function above deconfinement, we find that ground state charmonia (J/psi and eta_c) exist in the deconfined phase at least up to temperatures as high as 1.5Tc. P-wave charmonia (chi_c) on the other hand are dissociated already at 1.12Tc.Comment: Contribution to Lattice 2003 (non-zero) LaTeX, 3 pages, 3 figures, uses espcrc2 styl

Lee-Yang zero analysis for the study of QCD phase structure

We comment on the Lee-Yang zero analysis for the study of the phase structure of QCD at high temperature and baryon number density by Monte-Carlo simulations. We find that the sign problem for non-zero density QCD induces a serious problem in the finite volume scaling analysis of the Lee-Yang zeros for the investigation of the order of the phase transition. If the sign problem occurs at large volume, the Lee-Yang zeros will always approach the real axis of the complex parameter plane in the thermodynamic limit. This implies that a scaling behavior which would suggest a crossover transition will not be obtained. To clarify this problem, we discuss the Lee-Yang zero analysis for SU(3) pure gauge theory as a simple example without the sign problem, and then consider the case of non-zero density QCD. It is suggested that the distribution of the Lee-Yang zeros in the complex parameter space obtained by each simulation could be more important information for the investigation of the critical endpoint in the $(T, \mu_q)$ plane than the finite volume scaling behavior.Comment: 16 pages, 3 figures, 2 tables, minor change

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