I=2 Pion Scattering Length from Two-Pion Wave Functions

We calculate the two-pion wave function in the ground state of the I=2 $S$-wave system and find the interaction range between two pions, which allows us to examine the validity of the necessary condition for the finite-volume method for the scattering length proposed by L\"uscher. We work in the quenched approximation employing a renormalization group improved gauge action for gluons and an improved Wilson action for quarks at $1/a=1.207(12) {\rm GeV}$ on $16^3 \times 80$, $20^3 \times 80$ and $24^3 \times 80$ lattices. We conclude that the necessary condition is satisfied within the statistical errors for the lattice sizes $L\ge 24$ ($3.92 {\rm fm}$) when the quark mass is in the range that corresponds to $m_\pi^2 = 0.273-0.736 {\rm GeV}^2$. We obtain the scattering length with a smaller statistical error from the wave function than from the two-pion time correlator.Comment: LaTeX2e, 34 pages, 11 eps figures, uses revtex4 and graphic

Maximum entropy analysis of hadron spectral functions and excited states in quenched lattice QCD

Employing the maximum entropy method we extract the spectral functions from meson correlators at four lattice spacings in quenched QCD with the Wilson quark action. We confirm that the masses and decay constants, obtained from the position and the area of peaks, agree well with the results from the conventional exponential fit. For the first excited state, we obtain $m_{\pi_1} = 660(590)$ MeV, $m_{\rho_1} = 1540(570)$ MeV, and $f_{\rho_1} = 0.085(36)$ in the continuum limit.Comment: Lattice2001(spectrum), 3 page

I=2 pion-pion scattering phase shift in the continuum limit calculated with two-flavor full QCD

We present a calculation of the scattering phase shift for the I=2 S-wave pion-pion system in the continuum limit with two-flavor full QCD. Calculations are made at three lattice spacings, using the finite volume method of L\"uscher in the center of mass frame, and its extension to the laboratory frame.Comment: Lattice2003(spectrum), 3 page

Spectral function and excited states in lattice QCD with maximum entropy method

We apply the maximum entropy method to extract the spectral functions for pseudoscalar and vector mesons from hadron correlators previously calculated at four different lattice spacings in quenched QCD with the Wilson quark action. We determine masses and decay constants for the ground and excited states of the pseudoscalar and vector channels from position and area of peaks in the spectral functions. We obtain the results, $m_{\pi_1} = 660(590)$ MeV and $m_{\rho_1} = 1540(570)$ MeV for the masses of the first excited state masses, in the continuum limit of quenched QCD. We also find unphysical states which have infinite mass in the continuum limit, and argue that they are bound states of two doublers of the Wilson quark action. If the interpretation is correct, this is the first time that the state of doublers is identified in lattice QCD numerical simulations

The ρ(1S,2S)\rho(1S,2S), ψ(1S,2S)\psi(1S,2S), Υ(1S,2S)\Upsilon(1S,2S) and ψt(1S,2S)\psi_t(1S,2S) mesons in a double pole QCD Sum Rule

We use the method of double pole QCD sum rule which is basically a fit with two exponentials of the correlation function, where we can extract the masses and decay constants of mesons as a function of the Borel mass. We apply this method to study the mesons: $\rho(1S,2S)$, $\psi(1S,2S)$, $\Upsilon(1S,2S)$ and $\psi_t(1S,2S)$. We also present predictions for the toponiuns masses $\psi_t(1S,2S)$ of m(1S)=357 GeV and m(2S)=374 GeV.Comment: 14 pages, 11 figures in Braz J Phys (2016

News from Lattice QCD on Heavy Quark Potentials and Spectral Functions of Heavy Quark States

We discuss recent lattice results on in-medium properties of hadrons and focus on thermal properties of heavy quark bound states. We will clarify the relation between heavy quark free energies and potentials used to analyze the melting of heavy quark bound states. Furthermore, we present calculations of meson spectral functions which indicate that the charmonium ground states, J/psi and eta_c, persist in the quark gluon plasma as well defined resonances with no significant change of their zero temperature masses at least up to T ~ 1.5 T_c. We also briefly comment on the current status of lattice calculations at non-vanishing baryon number density.Comment: Plenary talk at the 17th International Conference on Ultra Relativistic Nucleus-Nucleus Collisions (Quark Matter 2004), Oakland, California, 11-17 Jan 2004. Submitted to J.Phys.

Spectral function and excited states in lattice QCD with the maximum entropy method

We apply the maximum entropy method to extract the spectral functions for pseudoscalar and vector mesons from hadron correlators previously calculated at four different lattice spacings in quenched QCD with the Wilson quark action. We determine masses and decay constants for the ground and excited states of the pseudoscalar and vector channels from the position and area of peaks in the spectral functions. We obtain the results mp1=660(590) MeV and mr 1=1540(570) MeV for the first excited state masses, in the continuum limit of quenched QCD. We also find unphysical states that have an infinite mass in the continuum limit, and argue that they are bound states of two doublers of the Wilson quark action. If the interpretation is correct, this is the first time that the state of doublers has been identified in lattice QCD numerical simulations