Search

We present physical results for a variety of light hadronic quantities obtained via a combined analysis of three 2+1 flavour domain wall fermion ensemble sets. For two of our ensemble sets we used the Iwasaki gauge action with beta=2.13 (a^-1=1.75(4) GeV) and beta=2.25 (a^-1=2.31(4) GeV) and lattice sizes of 24^3 x 64 and 32^3 x 64 respectively, with unitary pion masses in the range 293(5)-417(10) MeV. The extent L_s for the 5^th dimension of the domain wall fermion formulation is L_s=16 in these ensembles. In this analysis we include a third ensemble set that makes use of the novel Iwasaki+DSDR (Dislocation Suppressing Determinant Ratio) gauge action at beta = 1.75 (a^-1=1.37(1) GeV) with a lattice size of 32^3 x 64 and L_s=32 to reach down to partially-quenched pion masses as low as 143(1) MeV and a unitary pion mass of 171(1) MeV, while retaining good chiral symmetry and topological tunneling. We demonstrate a significant improvement in our control over the chiral extrapolation, resulting in much improved continuum predictions for the above quantities. The main results of this analysis include the pion and kaon decay constants, f_\pi=127(3)_{stat}(3)_{sys} MeV and f_K = 152(3)_{stat}(2)_{sys} MeV respectively (f_K/f_\pi = 1.199(12)_{stat}(14)_{sys}); the average up/down quark mass and the strange-quark mass in the MSbar-scheme at 3 GeV, m_{ud}(MSbar, 3 GeV) = 3.05(8)_{stat}(6)_{sys} MeV and m_s(MSbar, 3 GeV) = 83.5(1.7)_{stat}(1.1)_{sys}; the neutral kaon mixing parameter in the MSbar-scheme at 3 GeV, B_K(MSbar,3 GeV) = 0.535(8)_{stat}(13)_{sys}, and in the RGI scheme, \hat B_K = 0.758(11)_{stat}(19)_{sys}; and the Sommer scales r_1 = 0.323(8)_{stat}(4)_{sys} fm and r_0 = 0.480(10)_{stat}(4)_{sys} (r_1/r_0 = 0.673(11)_{stat}(3)_{sys}). We also obtain values for the SU(2) ChPT effective couplings, \bar{l_3} = 2.91(23)_{stat}(7)_{sys}$ and \bar{l_4} = 3.99(16)_{stat}(9)_{sys}., Comment: 95 pages, 23 figures. Added missing author to metadata

This is a follow-up to our earlier work on the energies and radial distributions of heavy-light mesons. The heavy quark is taken to be static (infinitely heavy) and the light quark has a mass about that of the strange quark. We now concentrate on the energies of the excited states with higher angular momentum and with a radial node. A new improvement is the use of hypercubic blocking in the time direction. The calculation is carried out with dynamical fermions on a 16 cubed times 32 lattice with a lattice spacing approximately 0.1 fm generated using a non-perturbatively improved clover action. In nature the closest equivalent of this heavy-light system is the B_s meson, which allows us to compare our lattice calculations to experimental results (where available) or to give a prediction where the excited states, particularly P-wave states, should lie. We pay special attention to the spin-orbit splitting, to see which one of the states (for a given angular momentum L) has the lower energy. An attempt is made to understand these results in terms of the Dirac equation., Comment: 35 pages. v3: Data from two new lattices added. New results in several chapters

This is a follow-up to our earlier work for the energies and the charge (vector) and matter (scalar) distributions for S-wave states in a heavy-light meson, where the heavy quark is static and the light quark has a mass about that of the strange quark. We study the radial distributions of higher angular momentum states, namely P- and D-wave states, using a "fuzzy" static quark. A new improvement is the use of hypercubic blocking in the time direction, which effectively constrains the heavy quark to move within a 2a hypercube (a is the lattice spacing). The calculation is carried out with dynamical fermions on a 16^3 times 32 lattice with a lattice spacing approximately 0.10 fm generated using the non-perturbatively improved clover action. The configurations were generated by the UKQCD Collaboration using lattice action parameters beta = 5.2, c_SW = 2.0171 and kappa = 0.1350. In nature the closest equivalent of this heavy-light system is the B_s meson. Attempts are now being made to understand these results in terms of the Dirac equation., Comment: Presented at XXIV International Symposium on Lattice Field Theory (Lattice 2006, Tucson, Arizona)

We compute the masses of the flavour singlet 0++ mesons using (n_f=2) unquenched lattice QCD with the Iwasaki and Wilson gauge actions. Both fermionic and glueball interpolating operators are used to create the states. The mass of the lightest 0++ meson is suppressed relative to the mass of the 0++ glueball in quenched QCD at an equivalent lattice spacing. We discuss two possible physical reasons for this.

We review the theory that predicts that the decay constant of the excited light pseudo-scalar mesons are suppressed in the chiral limit relative to the pion decay constant. We compute the decay constant of the first excited pion ($\pi^\prime$) using unquenched QCD at a fixed lattice spacing with sea quarks of mass as low as a third the mass of the strange quark. The final result is very sensitive to the improvement conditions. We obtain $f_{\pi^\prime} / f_{\pi}$ = 0.078(93) in the chiral limit., Comment: Updated references. Clarified discussion around equations 2 and 3

We review some decays that require knowledge of the decay constants of $0^{+}$ heavy-light mesons. We compute the decay constants of P-wave heavy-light mesons from unquenched lattice QCD, with two degenerate flavours of sea quarks, at a single lattice spacing. The lightest sea quark mass used in the calculation is a third of the strange quark mass. For the charm-strange meson we obtain the decay constant: $f_{D_{s 0^+}} = 340(110)$ MeV using our normalisation conventions. We obtain the $f_{P_s}^{static}$ (static-strange P-wave) decay constant as $302(39)$ MeV., Comment: We have included a effective mass plot and a graph for the chiral extrapolation in the light quark mass. Some of the discussions are clarified. No change in results. Accepted for publication in Phys.Rev.D

This is a follow-up to our earlier work [Phys. Rev. D 65, 014512 (2002); Eur. Phys. J. C 28, 79 (2003); Phys. Rev. D 69, 094505 (2004)] for the energies and the charge (vector) and matter (scalar) distributions for S-wave states in a heavy-light meson, where the heavy quark is static and the light quark has a mass about that of the strange quark. We study the radial distributions of higher angular momentum states, namely P- and D-wave states. In nature the closest equivalent of this heavy-light system is the B_s meson. The calculation is carried out with dynamical fermions on a 16^3 times 32 lattice with a lattice spacing of about 0.10 fm generated with the non-perturbatively improved clover action. It is shown that several features of the energies and radial distributions are in qualitative agreement with what one expects from a simple one-body Dirac equation interpretation., Comment: 6 pages, poster presented at Lattice 2005 (Heavy quarks)

This is a follow-up to our earlier work for the charge (vector) and matter (scalar) distributions for S-wave states in a heavy-light meson, where the heavy quark is static and the light quark has a mass about that of the strange quark. The calculation is again carried out with dynamical fermions on a 16^3x24 lattice with a lattice spacing of about 0.14 fm. It is shown that several features of the S- and P-wave distributions are in qualitative agreement with what one expects from a simple one-body Dirac equation interpretation., Comment: 5 pages, 2 figures, Quark Confinement and the Hadron Spectrum VI, Sardinia, Italy, September, 2004

Using the clover fermion action in unquenched QCD with pion masses as low as 420 MeV, we look for evidence for chiral logs in the static-light decay constant. There is some evidence for a chiral log term, if the original static theory of Eichten and Hill is used. However, the more precise data from the static action of the ALPHA collaboration do not show any evidence for non-linear dependence of the static-light decay constant on the light quark mass. We make some comments on the connection between chiral perturbation theory for decay constants of the pion and static-light meson.

We discuss some of the implications of simulating QCD when the action used for the sea quarks is different from that used for the valence quarks. We present exploratory results for the hadron mass spectrum and pseudoscalar meson decay constants using improved staggered sea quarks and HYP-smeared overlap valence quarks. We propose a method for matching the valence quark mass to the sea quark mass and demonstrate it on UKQCD clover data in the simpler case where the sea and valence actions are the same., Comment: 15 pages, 10 figures some minor modification to text and figures. Accepted for publication

We present results for the static-light meson from unquenched lattice QCD. The unquenched gauge configurations were generated using the non-perturbatively improved clover action. At the fixed lattice spacing of 0.1 fm the lightest sea quark mass used is a third of the strange quark mass. A comparison is made between heavy-light chiral perturbation theory and the f_B^(static) decay constant. The mass of the bottom quark is also reported: m_b(m_b) = 4.25(2)(11) GeV, where the first error is statistical and the last error is the systematic uncertainty., Comment: Poster presented at Lattice2004(heavy), Fermilab, June 21-26, 2004. 3 pages

We compute the charm quark mass in lattice QCD and compare different formulations of the heavy quark, and quenched data to that with dynamical sea quarks. We take the continuum limit of the quenched data by extrapolating from three different lattice spacings, and compare to data with two flavours of dynamical sea quarks with a mass around the strange at the coarsest lattice spacing. Both the FNAL and ALPHA formalism are used. We find the different heavy quark formulations have the same continuum limit in the quenched approximation, and limited evidence that this approximation overestimates the charm quark mass., Comment: Lattice2004(heavy) 3 pages, 2 figures

We present exploratory results for the hadron mass spectrum and pseudoscalar meson decay constants using mixed actions. We use improved staggered sea quarks and HYP-smeared overlap valence quarks. We obtain good signals on 10 configurations at one lattice spacing and two different sets of sea quark masses., Comment: Lattice2004(spectrum), 3pages, 4 figures

We compute the b quark mass from dynamical lattice QCD with clover quarks. The calculation is done at a fixed lattice spacing with sea quark masses as low as half the strange quark mass. Our final result is m_b(m_b} = 4.25(2)(11) GeV, where the first error is statistical and the last error is the systematic uncertainty., Comment: 10 pages

We report calculations of the parameter B_K appearing in the Delta S=2 neutral kaon mixing matrix element, whose uncertainty limits the power of unitarity triangle constraints for testing the standard model or looking for new physics. We use two flavours of dynamical clover-improved Wilson lattice fermions and look for dependence on the dynamical quark mass at fixed lattice spacing. We see some evidence for dynamical quark effects and in particular B_K decreases as the sea quark masses are reduced towards the up/down quark mass., Comment: 17 pages, 4 figures, uses JHEP3.cls, added comments and references

We compute the strange quark mass $m_s$ and the average of the $u$ and $d$ quark masses $\hat m$ using full lattice QCD with three dynamical quarks combined with experimental values for the pion and kaon masses. The simulations have degenerate $u$ and $d$ quarks with masses $m_u=m_d\equiv \hat m$ as low as $m_s/8$, and two different values of the lattice spacing. The bare lattice quark masses obtained are converted to the $\msbar$ scheme using perturbation theory at $O(alpha_s)$. Our results are: $m_s^\msbar$(2 GeV) = 76(0)(3)(7)(0) MeV, $\hat m^\msbar$(2 GeV) = 2.8(0)(1)(3)(0) MeV and $m_s/\hat m$ = 27.4(1)(4)(0)(1), where the errors are from statistics, simulation, perturbation theory, and electromagnetic effects, respectively., Comment: 5 pages, revtex, 2 figures. v2: New ms/hat(m) discussion and reference, v3: slight change in discussion of reference

We explore the transitions B$(0^+)$ to B $\pi$ and B$_s(0^+)$ to B K from lattice QCD with $N_f=2$ flavours of sea quark, using the static approximation for the heavy quark. We evaluate the effective coupling constants, predicting a B$(0^+)$ to B $\pi$ width of around 160 MeV. Our result for the coupling strength adds to the evidence that the B$_s(0^+)$ meson is not predominantly a molecular state (BK)., Comment: 10 pages LATEX

We explore the splitting between flavour singlet and non-singlet mesons in charmonium. This has implications for the hyperfine splitting in charmonium.

We determine the energies of the excited states of a heavy-light meson $Q\bar{q}$, with a static heavy quark and light quark with mass approximately that of the strange quark from both quenched lattices and with dynamical fermions. We are able to explore the energies of orbital excitations up to L=3, the spin-orbit splitting up to L=2 and the first radial excitation. These $b \bar{s}$ mesons will be very narrow if their mass is less than 5775 MeV -- the $BK$ threshold. We investigate this in detail and present evidence that the scalar meson (L=1) will be very narrow and that as many as 6 $b \bar{s}$ excited states will have energies close to the $BK$ threshold and should also be relatively narrow., Comment: 17 pages, 6 ps figures

We determine the mass of the charm quark ($m_c$) from lattice QCD with two flavors of dynamical quarks with a mass around the strange quark. We compare this to a determination in quenched QCD which has the same lattice spacing (0.1 fm). We investigate different formulations of the quark mass, based on the Vector Ward Identity, PCAC relation and the FNAL heavy quark formalism. Based on these preliminary results we find no effects due to sea quarks with a mass around strange., Comment: Presented at 21st International Symposium on Lattice Field Theory (LATTICE 2003), Tsukuba, Japan, 15-19 July, 2003

We discuss strategies to determine hadronic decay couplings from lattice studies. As an application, we explore the decay of a vector meson to two pseudoscalar mesons with $N_f=2$ flavours of sea quark. Although we are working with quark masses that do not allow a physical decay, we show how the transition rate can be evaluated from the amplitude for $\rho \to \pi \pi$ and from the annihilation component of $\pi \pi \to \pi \pi$. We explore the decay amplitude for two different pion momenta and find consistent results. The coupling strength we find is in agreement with experiment. We also find evidence for a shift in the $\rho$ mass caused by mixing with two pion states., Comment: Proc. Latt03 (spectrum), 3 pages, 4 figs

We explore the decay of a vector meson to two pseudoscalar mesons on the lattice with $N_f=2$ flavours of sea quark. Although we are working with quark masses that do not allow a physical decay, we show how the transition rate can be evaluated from the amplitude for $\rho \to \pi \pi$ and from the annihilation component of $\pi \pi \to \pi \pi$. We explore the decay amplitude for two different pion momenta and find consistent results. The coupling strength we find is in agreement with experiment. We also find evidence for a shift in the $\rho$ mass caused by mixing with two pion states., Comment: 13 pages, version as accepted for Physics Letters B

We measure the spectrum of low-lying nucleon resonances using Bayesian fitting methods. We compare the masses obtained in the quenched approximation to those obtained with two flavours of dynamical fermions at a matched lattice spacing. At the pion masses employed in our simulations, we find that the mass of the first positive-parity nucleon excitation is always greater than that of the parity partner of the nucleon., Comment: Lattice2002(spectrum) 3 pages, 4 figures

We compute the mass of the singlet 0++ state using both (psi_bar psi) and Wilson loop operators from a N_f=2 lattice QCD calculation., Comment: Lattice2002(spectrum)

A knowledge of the radial distributions of quarks inside hadrons could lead to a better understanding of the QCD description of these hadrons and possibly suggest forms for phenomenological models. As a step in this direction, in an earlier work, the charge (vector) and matter (scalar) radial distributions of heavy-light mesons were measured in the quenched approximation on a 16^3x24 lattice with a lattice spacing of 'a' approx. 0.17 fm, and a hopping parameter corresponding to a light quark mass about that of the strange quark. Here several improvements are now made: 1) The configurations are generated using dynamical fermions with a approx 0.14 fm; 2) Many more gauge configurations areincluded; 3) The distributions at many off-axis, in addition to on-axis, points are measured; 4) The data analysis is much more complete. In particular, distributions involving excited states are extracted. The exponential decay of the charge and matter distributions can be described by mesons of mass 0.9 +- 0.1 and 1.5 +- 0.1 GeV respectively -- values that are consistent with those of vector and scalar $q\bar{q}$-states calculated directly with the same lattice parameters., Comment: 35 pages, 6 figures, Latex

The form factors for the semi-leptonic B->D and B->D* decays are evaluated in quenched lattice QCD at two different values of the coupling, beta=6.0 and 6.2. The action and the operators are fully O(a) non-perturbatively improved. The slope of the Isgur-Wise function is evaluated, and found to be rho^2=0.83^{+15+24}_{-11-1} (quoted errors are statistical and systematic respectively). Ratios of form factors are evaluated and compared to experimental determinations., Comment: 21 pages, 10 figures

We discuss the allowed decays of a hybrid meson in the heavy quark limit. We deduce that an important decay will be into a heavy quark non-hybrid state and a light quark meson, in other words, the de-excitation of an excited gluonic string by emission of a light quark-antiquark pair. We discuss the study of hadronic decays from the lattice in the heavy quark limit and apply this approach to explore the transitions from a spin-exotic hybrid to $\chi_b \eta$ and $\chi_b S$ where $S$ is a scalar meson. We obtain a signal for the transition emitting a scalar meson and we discuss the phenomenological implications., Comment: 18 pages, LATEX, 3 ps figures

Simulations that use the clover action in quenched QCD calculations have a lower limit to the quark mass that can be reached, because of the fluctuations caused by exceptional configurations. From this low statistics study, we find that the twisted clover action, recently introduced by the ALPHA collaboration, can be used to simulate quenched QCD at quark masses below those attainable by simulations that use the clover action., Comment: Lattice2001(spectrum)

We present the results of a calculation of semileptonic form factors of D and B mesons. The calculation uses nonperturbatively order a improved quenched lattice QCD and two values of the coupling. Results for charm mesons show reasonable agreement with experiment. The lattice results for B -> rho l nu are compared with high q^2 experimental results., Comment: Contribution to Lattice 2001 (heavy quarks); 3 pages, 4 figures. Typo corrected

We present results for the leptonic decays of heavy-light mesons in the quenched approximation and a preliminary result for f_Ds with dynamical fermions for Nf=2. We examine the systematic effects of extrapolating the decay constants from the charm to the bottom quark mass, and find this extrapolation to be under control. We present a preliminary result for f_Ds{Nf=2} and compare to f_Ds{Nf=0} matched to have the same lattice spacing set by the Sommer scale, r0. We find no significant difference., Comment: Lattice2001(heavyquark) 3 pages, 3 figures. Report number corrected

The h+, h_A1 form factors for the semi-leptonic B->D and B->D* decays are evaluated in quenched lattice QCD with beta=6.2. The action and the operators are fully O(a) non-perturbatively improved. The Isgur-Wise function is evaluated and fitted to extract its slope; the latter is found to be rho^2=1.1(2)(3) from the B->D* decay and rho^2=1.0(2)(3) from the B->D decay. The form factors ratios R_1, R_2 are evaluated and found to be in agreement with experimental determinations., Comment: Lattice 2001 proc., 3 pages, 3 figures

We calculate the light `glueball' mass spectrum in N_f=2 lattice QCD using a fermion action that is non-perturbatively O(a) improved. We work at lattice spacings a ~0.1 fm and with quark masses that range down to about half the strange quark mass. We find the statistical errors to be moderate and under control on relatively small ensembles. We compare our mass spectrum to that of quenched QCD at the same value of a. Whilst the tensor mass is the same (within errors), the scalar mass is significantly smaller in the dynamical lattice theory, by a factor of ~(0.84 +/- 0.03). We discuss what the observed m_q dependence of this suppression tells us about the dynamics of glueballs in QCD. We also calculate the masses of flux tubes that wind around the spatial torus, and extract the string tension from these. As we decrease the quark mass we see a small but growing vacuum expectation value for the corresponding flux tube operators. This provides clear evidence for `string breaking' and for the (expected) breaking of the associated gauge centre symmetry by sea quarks., Comment: 33pp LaTeX. Version to appear in Phys. Rev. D

We study the topological susceptibility, chi, in QCD with two quark flavours using lattice field configurations that have been produced with an O(a) improved quark action. We find clear evidence for the expected suppression at small quark mass, and examine the variation of chi with this mass. The resulting estimate of the pion decay constant, f_pi = 105 +/- 6 ^{+18}_{-10} MeV, is consistent with the experimental value of ~93 MeV. We compare chi to the large-N_c prediction and find consistency over a large range of quark masses. We discuss the benefits of the non-perturbative action improvement scheme and of the stategy of keeping the lattice spacing (nearly) fixed as the quark mass is varied. We compare our results with other studies and suggest why such a quark mass dependence has not always been seen., Comment: LaTeX. Supercedes our preprint hep-ph/0004180. Version to appear in Phys. Lett. B

We report on determinations of the low-energy constants alpha5 and alpha8 in the effective chiral Lagrangian at O(p^4), using lattice simulations with N_f=2 flavours of dynamical quarks. Precise knowledge of these constants is required to test the hypothesis whether or not the up-quark is massless. Our results are obtained by studying the quark mass dependence of suitably defined ratios of pseudoscalar meson masses and matrix elements. Although comparisons with an earlier study in the quenched approximation reveal small qualitative differences in the quark mass behaviour, numerical estimates for alpha5 and alpha8 show only a weak dependence on the number of dynamical quark flavours. Our results disfavour the possibility of a massless up-quark, provided that the quark mass dependence in the physical three-flavour case is not fundamentally different from the two-flavour case studied here., Comment: references added, typos corrected

We present results for the static inter-quark potential, lightest glueballs, light hadron spectrum and topological susceptibility using a non-perturbatively improved action on a $16^3\times 32$ lattice at a set of values of the bare gauge coupling and bare dynamical quark mass chosen to keep the lattice size fixed in physical units ($\sim 1.7$ fm). By comparing these measurements with a matched quenched ensemble, we study the effects due to two degenerate flavours of dynamical quarks. With the greater control over residual lattice spacing effects which these methods afford, we find some evidence of charge screening and some minor effects on the light hadron spectrum over the range of quark masses studied ($M_{PS}/M_{V}\ge0.58$). More substantial differences between quenched and unquenched simulations are observed in measurements of topological quantities., Comment: 53 pages, LaTeX/RevTeX, 16 eps figures; corrected clover action expression and various typos, no results changed

We study the flavour singlet mesons from first principles using lattice QCD. We explore the splitting between flavour singlet and non-singlet for vector and axial mesons as well as the more commonly studied cases of the scalar and pseudoscalar mesons., Comment: 12 pages, LATEX, 4 ps figures

We present a calculation of the mass of the lowest-lying negative-parity J=1/2- state in quenched QCD. Results are obtained using a non-perturbatively O(a)-improved clover fermion action, and a splitting is found between the mass of the nucleon and its parity partner. The calculation is performed on two lattice volumes and at three lattice spacings, enabling a study of both finite-volume and finite lattice-spacing uncertainties. A comparison is made with results obtained using the unimproved Wilson fermion action., Comment: 13 pages, 8 figures, revtex Version accepted for publication in Physics Letters B. Some changes to discussion of chiral extrapolations; primary results unchanged

In nuclear many-body problems the short-range correlation between two nucleons is well described by the corresponding correlation in the {two}-body problem. Therefore, as a first step in any attempt at an analogous description of many-quark systems, it is necessary to know the two-quark correlation. With this in mind, we study the light quark distribution in a heavy-light meson with a static heavy quark. The charge and matter radial distributions of these heavy-light mesons are measured on a lattice with a light quark mass about that of the strange quark. Both distributions can be well fitted upto r approx 0.7 fm with the exponential form w_i^2(r), where w_i(r)=A exp(-r/r_i). For the charge(c) and matter(m) distributions r_c approx 0.32(2) fm and r_m \approx 0.24(2) fm. We also discuss the normalisation of the total charge (defined to be unity in the continuum limit) and matter integrated over all space, finding 1.30(5) and 0.4(1) respectively for a lattice spacing approx 0.17 fm., Comment: 8 pages, 3 ps figures

For a heavy-light meson with a static heavy quark, we can explore the light quark distribution. The charge and matter radial distributions of these heavy-light mesons are measured on a 16^3 * 24 lattice at beta=5.7 and a hopping parameter corresponding to a light quark mass about that of the strange quark. Both distributions can be well fitted up to 4 lattice spacings (r approx 0.7 fm) with the exponential form w_i^2(r), where w_i(r)=A exp(-r/r_i). For the charge(c) and matter(m) distributions r_c approx 0.32(2) fm and r_m approx 0.24(2) fm. We also discuss the normalisation of the total charge and matter integrated over all space, finding 1.30(5) and 0.4(1) respectively., Comment: 31 pages including 7 ps figures

We describe the bottomonium spectrum obtained on the UKQCD dynamical ensembles and its comparison to quenched results. We include a determination of alpha_s and m_b from the dynmaical results., Comment: Lattice 2000 (Heavy Quark Physics)

We present results of quenched lattice calculations of the matrix elements relevant for B_d-\bar B_d and B_s-\bar B_s mixing in the Standard Model. Results for the corresponding SU(3)-breaking ratios, which can be used to constrain or determine |V_{td}|, are also given. The calculations are performed at two values of the lattice spacing, corresponding to \beta = 6.0 and \beta = 6.2, with quarks described by a mean-field-improved Sheikholeslami-Wohlert action. As a by-product, we obtain the leptonic decay constants of B and D mesons. We also present matrix elements relevant for D^0-\bar D^0 mixing. Our results are summarized in the Introduction., Comment: 27 pages (RevTeX), 26 figures, version published in Phys. Rev. D: improved estimate of the systematic error associated with the uncertainty on the strange quark mass and other small improvements to analysis (results change only slightly); correction of typos and minor changes to text; RevTeX formatting

The construction of operators and calculational methods for the determination of the N* spectrum are discussed. The masses of the parity partners of the nucleon and delta are computed from the O(a)-improved data of the UKQCD Collaboration, and a clear splitting observed between the mass of the nucleon and its parity partner., Comment: Lattice 2000 (subject), 4 pages, 5 postscript figures

We discuss in detail the extraction of hadronic mixing strengths from lattice studies. We apply this to the mixing of a scalar glueball and a scalar meson in the quenched approximation. We also measure correlations appropriate for flavour-singlet scalar mesons using dynamical quark configurations from UKQCD. This enables us to compare the results from the quenched study of the mixing with the direct determination of the mixed spectrum. Improved methods of evaluating the disconnected quark diagrams are also presented., Comment: 23 pages, 5 postscript figures

We present results for the semi-leptonic and leptonic decays of B mesons. These non-perturbative matrix elements are important for constraining the CKM matrix. Results are presented for the pseudoscalar and vector decay constants, as well as flavour breaking ratios and heavy quark symmetry relations. We consider the chiral and momentum dependence of the semi-leptonic form factors of the decay B-> pi l nu and the soft pion relation (SPR) on the lattice. These calculations were performed in the quenched approximation at two values of the coupling with non-perturbatively order a improved action and currents., Comment: LAT2000 (Heavy quarks) 4 pages 4 figures

A brief review is given of attempts to understand the energies of four-quark systems calculated on a lattice in terms of nuclear-physics-inspired many-body techniques involving interquark potentials. Results are given for the next stage of this study where the wavefunctions of heavy-light mesons are also calculated on a lattice., Comment: 3 pages, one figure. Contribution to Confinement IV held in Vienna, 2000

We study the topological susceptibility, chi, in two flavour lattice QCD. We find clear evidence for the expected suppression of chi at small quark mass. The estimate of the pion decay constant, f_pi = 105 +/-5 +18/-10 MeV, is consistent with the experimental value of approximately 93 MeV. We compare chi to the large-N_c prediction and find consistency over a large range of quark masses., Comment: A condensed hep-ph/0004180 (3 pages) presented at Confinement IV, Vienna, July 2000

We study the flavour singlet pseudoscalar mesons from first principles using lattice QCD. We explore the quark content of the $\eta$ and $\eta'$ mesons and we discuss their decay constants., Comment: Figure 1 corrected

We study the topological susceptibility, chi, in QCD with two quark flavours using the lattice field configurations recently produced by the UKQCD collaboration. We find clear evidence for the expected suppression at small quark mass, and examine the variation of chi with this mass. The resulting estimate of the pion decay constant, f_pi = 105 +/- 5 +18/-10 MeV, is consistent with the experimental value of approximately 93 MeV. We compare chi to the large-N_c prediction and find consistency over a large range of quark masses. The benefits of the non-perturbative action improvement scheme and the matched lattice spacings between simulation ensembles are discussed. We compare our results with other studies and suggest a reason why such a quark mass dependence has not been previously seen., Comment: 18 pp of LaTeX. No change to content between versions. Talk presented at the IoP Particle Physics 2000 conference in Edinburgh. Not for publication; superceded by our paper hep-lat/0108006

The crossing from a static quark-antiquark system to a system of two static-light mesons when the separation of the static quarks is increased is calculated in zero-temperature lattice QCD. The mixing of these two states is extracted from the lattice operators. We also discuss the breaking of an excited string of a hybrid meson., Comment: 4 pages, 2 eps figures

We report on our progress in using the overlap-Dirac fermion operator in simulations of lattice QCD. We have investigated the Lanczos based method of Borici, as well as various rational approximations, to calculate the step function in the overlap-Dirac operator. The QCD simulations were performed at beta = 5.85 with a lattice volume of 8**3*32., Comment: Talk given at CHIRAL '99, Taipei, Sep. 13-18, 1999. 9 pages