Masayuki Wakayama

Lattice QCD study of four-quark components of the isosinglet scalar mesons: Significance of disconnected diagrams

We study the possible significance of four-quark states in the isosinglet scalar mesons (JPC=0++, I=0) by performing two-flavor full lattice QCD simulations on an 83×16 lattice using the improved gauge action and the clover-improved Wilson quark action. In particular, we evaluate the propagators of molecular and tetraquark operators together with singly disconnected diagrams. In the computation of the singly disconnected diagrams we employ the Z2-noise method with the truncated eigenmode approach. We show that the quark loops given by the disconnected diagrams play an essential role in propagators of tetraquark and molecular operators.

Analysis of the scalar mesons on the Lattice

We study the possibility that the scalar mesons exist as four-quark states. The energy shift of two pseudoscalar mesons as a function of spatial lattice size makes a distinction between bound states and scattering states of four-quark states. We calculate the four-quark state in the quenched approximation, ignoring the two-quark annihilation diagrams and the vacuum channels. We perform a calculation of pseudoscalar meson scattering amplitudes, using N f = 2 Wilson fermion and plaquette/Iwasaki gauge actions. We obtain the indication that the four-quark states in the case of the isospin zero (I = 0) and two (I = 2) channels are no bound states. And we find that the bound energy depends strongly on pion mass rather than the ratio of pion mass to rho meson mass.

Lattice QCD at finite baryon density using analytic continuation

We simulate lattice QCD with two flavors of Wilson fermions at imaginary baryon chemical potential. Results for the baryon number density computed in the confining and deconfining phases at imaginary baryon chemical potential are used to determine the baryon number density and higher cumulants at the real chemical potential via analytical continuation.