Jonathan M. Flynn

Physical results from 2+1 flavor domain wall QCD and SU(2) chiral perturbation theory

We have simulated QCD using 2+1 flavors of domain wall quarks on a (2.74fm)3 volume with an inverse lattice scale of a?1=1.729(28) GeV. The up and down (light) quarks are degenerate in our calculations and we have used four values for the ratio of light quark masses to the strange (heavy) quark mass in our simulations: 0.217, 0.350, 0.617 and 0.884. We have measured pseudoscalar meson masses and decay constants, the kaon bag parameter BK and vector meson couplings. We have used SU(2) chiral perturbation theory, which assumes only the up and down quark masses are small, and SU(3) chiral perturbation theory to extrapolate to the physical values for the light quark masses. While next-to-leading order formulae from both approaches fit our data for light quarks, we find the higher order corrections for SU(3) very large, making such fits unreliable. We also find that SU(3) does not fit our data when the quark masses are near the physical strange quark mass. Thus, we rely on SU(2) chiral perturbation theory for accurate results. We use the masses of the ? baryon, and the ? and K mesons to set the lattice scale and determine the quark masses. We then find f?=124.1(3.6)stat(6.9)systMeV, fK=149.6(3.6)stat(6.3)systMeV and fK/f?=1.205(0.018)stat(0.062)syst. Using non-perturbative renormalization to relate lattice regularized quark masses to RI-MOM masses, and perturbation theory to relate these to MS¯ we find mMS¯ud(2GeV)=3.72(0.16)stat(0.33)ren(0.18)systMeV and mMS¯s(2GeV)=107.3(4.4)stat(9.7)ren(4.9)systMeV.

Continuum limit physics from 2+1 flavor domain wall QCD

We present physical results obtained from simulations usin g 2+1 flavors of domain wall quarks and the Iwasaki gauge action at two values of the lattice spac ing a, (a−1= 1.73 (3) GeV and a−1= 2.28 (3) GeV). On the coarser lattice, with 24 3×64×16 points (where the 16 corresponds to Ls, the extent of the 5 th dimension inherent in the domain wall fermion (DWF) formula tion

Lattice-constrained parametrizations of form factors for semileptonic and rare radiative B decays

Abstract We describe all the form factors for semileptonic and radiative B decays to the same light vector meson with just two parameters and the two form factors for semileptonic B decays to a light pseudoscalar meson with a further two or three parameters. This provides simple parametrizations of the form factors for the physical B 0 →ρ + l − ν l , B 0 →π + l − ν l and B →K ∗ γ decays. The parametrizations are consistent with heavy quark symmetry, kinematic constraints and lattice results, which we use to determine the parameters. In addition, we test versions of the parametrizations consistent (or not) with light-cone sum rule scaling relations at q2=0.

Polychromatic penguins don't fly

Abstract It is shown that the large-N approximation in the standard model predicts much too small a rate for ΔI = 1 2 nonleptonic K decays, even when short-distance QCD effects such as penguins are included. The effects of the penguins are discussed consistently to leading nontrivial order in chiral perturbation theory and it is found that they are completely calculable and small. It is concluded that N = 3 is not large enough to make the large-N approximation useful.

Decay constants of B and D mesons from non-perturbatively improved lattice QCD

The decay constants of B and D mesons are computed in quenched lattice QCD at two dierent values of the coupling. The action and operators areO(a )i mproved with non-perturbative coecients where available. The results are fB = 218 +5 5 +5 41 MeV, fD = 220 +3 3 +2 24 MeV, fBs = 242 +4 4 +13 48 MeV, fDs = 241 +2 2 +7 30 MeV. Systematic errors are discussed in detail. Results for vector decay constants, avour symmetry breaking ratios of decay constants, the pseudoscalar-vector mass splitting and D meson masses are also presented.

Improved B→πlνl form factors from the lattice

Abstract We present the results of a lattice computation of the form factors for B 0 → π − l + ν l decays near zero-recoil. These results will allow a determination of the CKM matrix element | V ub | when measurements of the differential decay rate become available. We also provide models for extrapolation of the form factors and rate to the full recoil range. Our computation is performed in the quenched approximation to QCD on a 24 3 ×48 lattice at β =6.2, using a non-perturbatively O (a) -improved action. The masses of all light valence quarks involved are extrapolated to their physical values.

Form factors for B → πlνl and B → K∗γ decays on the lattice

We present a unified method for analysing form factors in B -> pi l nu-bar_l and B -> K* gamma decays. The analysis provides consistency checks on the q^2 and 1/M extrapolations necessary to obtain the physical decay rates. For the first time the q^2 dependence of the form factors is obtained at the B scale. In the B -> pi l nu-bar_l case, we show that pole fits to f^+ may not be consistent with the q^2 behaviour of f^0, leading to a possible factor of two uncertainty in the decay rate and hence in the value of |V_{ub}|^2 deduced from it. For B -> K* gamma, from the combined analysis of form factors T_1 and T_2, we find the hadronisation ratio R_{K^*} of the exclusive B -> K* gamma to the inclusive b -> s gamma rates is of order 35% or 15% for constant and pole-type behaviour of T_2 respectively.

K→π form factors with reduced model dependence

Using partially twisted boundary conditions we compute the K→π semi-leptonic form factors in the range of momentum transfers

The pion's electromagnetic form factor at small momentum transfer in full lattice QCD

0\lesssim q^{2}\leq q^{2}_{\max}=(m_{K}-m_{\pi})^{2}

A numerical study of partially twisted boundary conditions

in lattice QCD with Nf=2+1 dynamical flavours. In this way we are able to determine