We present results of our trial calculation of the $K to pipi$ decay amplitudes with the improved Wilson fermion action. Calculations are carried out with $N_f=2+1$ gauge configurations generated with the Iwasaki gauge action and non-perturbatively $
O(a)$-improved Wilson fermion action at $a=0.091,{rm fm}$, $m_pi=280,{rm MeV}$ and $m_K=560,{rm MeV} (sim 2 m_pi)$ on a $32^3times 64$ ($La=2.9 {rm fm}$) lattice.
We perform a lattice QCD study of the $rho$ meson decay from the $N_f=2+1$ full QCD configurations generated with a renormalization group improved gauge action and a non-perturbatively $O(a)$-improved Wilson fermion action. The resonance parameters,
the effective $rhotopipi$ coupling constant and the resonance mass, are estimated from the $P$-wave scattering phase shift for the isospin I=1 two-pion system. The finite size formulas are employed to calculate the phase shift from the energy on the lattice. Our calculations are carried out at two quark masses, $m_pi=410,{rm MeV}$ ($m_pi/m_rho=0.46$) and $m_pi=300,{rm MeV}$ ($m_pi/m_rho=0.35$), on a $32^3times 64$ ($La=2.9,{rm fm}$) lattice at the lattice spacing $a=0.091,{rm fm}$. We compare our results at these two quark masses with those given in the previous works using $N_f=2$ full QCD configurations and the experiment.
We present preliminary results on the $rho$ meson decay width from $N_f=2+1$ full QCD configurations generated by PACS-CS Collaboration. The decay width is estimated from the $P$-wave scattering phase shift for the isospin $I=1$ two-pion system. The
finite size formula presented by Luscher in the center of mass frame and its extension to non-zero total momentum frame by Rummukainen and Gottlieb are employed for the calculations of the phase shift. Our calculations are carried out at $m_pi=410 {rm MeV}$ ($m_pi/m_rho=0.46$) and $a=0.091 {rm fm}$ on a $32^3times 64$ ($La=2.9 {rm fm}$) lattice.
