Effects of staggered fermions and mixed actions on the scalar correlator

We provide the analytic predictions for the flavor non-singlet scalar correlator, which will enable determination of the scalar meson mass from the lattice scalar correlator. We consider simulations with 2+1 staggered sea quarks and staggered or chiral valence quarks. At small u/d masses the correlator is dominated by the bubble contribution, which is the intermediate state with two pseudoscalar mesons. We determine the bubble contribution within Staggered and Mixed Chiral Perturbation Theory. Its effective mass is smaller than the mass M_pi+M_eta, which is the lightest intermediate state in proper 2+1 QCD. The unphysical effective mass is a consequence of the taste breaking that makes possible the intermediate state with mass 2*M_pi. We find that the scalar correlator can be negative in the simulations with mixed quark actions if the sea and valence quark masses are tuned by matching the pion masses M_{val,val}=M_{pi_5}.Comment: 16 pages, 7 figure

Long distance contributions in D→VγD \to V \gamma decays

Using the factorization scheme for the nonleptonic $D \to V V_0$ weak amplitudes, we classify all diagrams which arise in $D \to V \gamma$ decays and calculate them with the help of the hybrid model which combines the heavy quark effective theory and the chiral Lagrangian approach. Thus we determine the long distance contribution to the amplitudes of Cabibbo allowed and Cabibbo suppressed $D \to V\gamma$ decays. The calculation of the expected range of the branching ratios of nine different $D \to V \gamma$ channels is compared with results of other approaches. The present work establishes an increase of the parity violating contribution in these decays in comparison with previous analyses.Comment: 15 pages, latex, 2 figures; we have changed Table 2 and the caption of Table 1. To be published in Eur. Phys.

Operators for scattering of particles with spin

Operators for simulating the scattering of two particles with spin are constructed. Three methods are shown to give the consistent lattice operators for PN, PV, VN and NN scattering, where P, V and N denote pseudoscalar meson, vector meson and nucleon. The projection method leads to one or several operators $O_{\Gamma,r,n}$ that transform according to a given irreducible representation $\Gamma$ and row r. However, it gives little guidance on which continuum quantum numbers of total J, spin S, orbital momentum L or single-particle helicities $\lambda_{1,2}$ will be related with a given operator. This is remedied with the helicity and partial-wave methods. There first the operators with good continuum quantum numbers $(J,P,\lambda_{1,2})$ or $(J,L,S)$ are constructed and then subduced to the irreps $\Gamma$ of the discrete lattice group. The results indicate which linear combinations $O_{\Gamma,r,n}$ of various n have to be employed in the simulations in order to enhance couplings to the states with desired continuum quantum numbers. The total momentum of two hadrons is restricted to zero since parity P is a good quantum number in this case.Comment: 7 pages, talk presented at the 34th International Symposium on Lattice Field Theory, 24-30 July 2016, Southampton, U