We present results of quenched lattice calculations of the matrix elements relevant for Bd−B̄d and Bs−B̄s mixing in the Standard Model. Results for the corresponding SU(3)-breaking ratios, which can be used to constrain or determine |Vtd|, are also given. The calculations are performed at two values of the lattice spacing, corresponding to β = 6.0 and β = 6.2, with quarks described by a mean-fiel...

Charmonia are flavour singlet mesons and thus in principle contributions from disconnected quark line diagrams might affect their masses, either directly or via mixing with other flavour singlet channels. We present a first study that takes both effects into account. We employ improved stochastic all-to-all propagator techniques (including new methods) to calculate the diagrams that appear with...

Perturbative estimates of operator coefficients for improved lattice actions are becoming increasingly important for precision simulations of many hadronic observables. Following previous work by Dimm, Lepage, and Mackenzie, we consider the feasibility of computing operator coefficients from numerical simulations deep in the perturbative region of lattice theories. Here we introduce a backgroun...

We compute the strangeness and light-quark contributions Δs, Δu, and Δd to the proton spin in n(f)=2 lattice QCD at a pion mass of about 285 MeV and at a lattice spacing a≈0.073 fm, using the nonperturbatively improved Sheikholeslami-Wohlert Wilson action. We carry out the renormalization of these matrix elements, which involves mixing between contributions from different quark flavors. Our mai...

severe overgrowth and tallness is very rare in human beings. the most common cause is gigantism due to the excessive secretion of the growth hormone, especially, before the closure of long bones’ epiphyseal growth plates. there are other rare disorders that are categorized on overgrowth syndromes. herein, we report an extremely rare, or even perhaps a unique, patient from iran. the clinical and...

We describe two ideas useful in the construction of highly improved quark actions for simulations on coarse lattices: (i) Field transformations solve the doubler problem without destroying tree-level improvement for onor off-shell quantities. The simplest example is the Sheikholeslami-Wohlert (clover) action. Going to the next order of improvement yields the class of D234 actions. (ii) Anisotro...

We investigate a tree-level O(a3)-accurate action, D234c, on coarse lattices. For the improvement terms we use tadpole-improved coefficients, with the tadpole contribution measured by the mean link in Landau gauge. We measure the hadron spectrum for quark masses near that of the strange quark. We find that D234c shows much better rotational invariance than the Sheikholeslami-Wohlert action, and...

We compute the light-hadron mass spectrum at b55.7 using the O(a)-improved Sheikholeslami-Wohlert fermion action with two choices of the clover coefficient: the classical value c51 and a mean-field or tadpole-improved estimate c51.57. We compare our results with those of the GF11 Collaboration who use the Wilson fermion action (c50). We find that changing c from zero to 1 and 1.57 leads to sign...

Quenched lattice QCD studies using WilsonDirac fermions have encountered large statistical errors in calculations involving very light quarks. A small subset of the gauge configurations seem to play a dominant role in the final results. These “exceptional configurations” have limited studies to quark masses much larger than the up and down quark masses. The large fluctuations resulting from the...

We calculate the critical value of the hopping parameter, κc, in O(a) improved Lattice QCD, to two loops in perturbation theory. We employ the Sheikholeslami-Wohlert (clover) improved action for Wilson fermions. The quantity which we study is a typical case of a vacuum expectation value resulting in an additive renormalization; as such, it is characterized by a power (linear) divergence in the ...