arXiv subjects
L. Lellouch
Publications and source records attributed to L. Lellouch.
A numerical treatment of Neuberger's lattice Dirac operator
We describe in some detail our numerical treatment of Neuberger's lattice Dirac operator as implemented in a practical application. We discuss the improvements we have found to accelerate the numerical computations and give an estimate of the expense when using this operator in practice.
An Investigation of the Soft Pion Relation in Quenched Lattice QCD
A lattice determination of the form factor and decay constants for the semileptonic decay of heavy pseudoscalar (PS) mesons at zero recoil is presented from which the soft pion relation is satisfied. Chiral extrapolation of the form factor is performed at constant $q^2$. Pole dominance is used to extrapolate the form factor in heavy quark mass. At the B mass, the form factor at zero recoil lies somewhat below the ratio of decay constants; the relation remains satisfied within error.
Finite-size scaling of the quark condensate in quenched lattice QCD
We confront the finite volume and small quark mass behaviour of the scalar condensate, determined numerically in quenched lattice QCD using Neuberger fermions, with predictions of quenched chiral perturbation theory. We find that quenched chiral perturbation theory describes the numerical data well, allowing us to extract the infinite volume, chiral limit scalar condensate, up to a multiplicative renormalization constant.
Dispersive Bounds on the Shape of B -> D^(*) l nu Form Factors
Dispersive constraints on the shape of the form factors which describe the exclusive decays B -> D^(*) l nu are derived by fully exploiting spin symmetry in the ground-state doublet of heavy-light mesons. The analysis includes all twenty B^(*) -> D^(*) semileptonic form factors. Heavy-quark symmetry, with both short-distance and 1/m_Q corrections included, is used to provide relations between the form factors near zero recoil. Simple one-parameter functions are derived, which describe the form factors in the semileptonic region with an accuracy of better than 2%. The implications of our results for the determination of |V_cb| are discussed.
First Lattice Study of Semileptonic Decays of Lambda_b and Xi_b Baryons
We present the results of the first lattice study of semileptonic decays of baryons containing a b-quark. Predictions for the decay distributions are given and the Isgur-Wise functions for heavy baryons are computed, for values of the velocity transfer up to about omega=1.2. The computations are performed on a 24^3 x 48 lattice at beta=6.2 using the Sheikholeslami-Wohlert action in the quenched approximation.
How small can the light quark masses be?
We derive lower bounds for the combination of light quark masses m_s +m_u and m_d +m_u. The derivation is based on first principles: the analyticity properties of two-point functions of local current operators and the positivity of the corresponding hadronic spectral functions. The bounds follow from the restriction of the sum over all possible hadronic states which can contribute to the hadronic spectral functions to those with the lowest invariant mass. These hadronic contributions are well known phenomenologically, either from experiment or from chiral perturbation theory calculations. The results we find cast serious doubts on the reliability of some of the lattice QCD determinations which have been recently reported.