348 research outputs found

    Quarkonium spin structure in lattice NRQCD

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    Numerical simulations of the quarkonium spin splittings are done in the framework of lattice nonrelativistic quantum chromodynamics (NRQCD). At leading order in the velocity expansion the spin splittings are of O(MQv4)O(M_Q v^4), where MQM_Q is the renormalized quark mass and v2v^2 is the mean squared quark velocity. A systematic analysis is done of all next-to-leading order corrections. This includes the addition of O(MQv6)O(M_Q v^6) relativistic interactions, and the removal of O(a2MQv4)O(a^2 M_Q v^4) discretization errors in the leading-order interactions. Simulations are done for both S- and P-wave mesons, with a variety of heavy quark actions and over a wide range of lattice spacings. Two prescriptions for the tadpole improvement of the action are also studied in detail: one using the measured value of the average plaquette, the other using the mean link measured in Landau gauge. Next-to-leading order interactions result in a very large reduction in the charmonium splittings, down by about 60% from their values at leading order. There are further indications that the velocity expansion may be poorly convergent for charmonium. Prelimary results show a small correction to the hyperfine splitting in the Upsilon system.Comment: 16 pages, REVTEX v3.1, 5 postscript figures include

    The Self-Energy of Massive Lattice Fermions

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    We address the perturbative renormalization of massive lattice fermions. We derive expressions-valid to all orders in perturbation theory and for all values of the bare fermion mass-for the rest mass, the kinetic mass, and the wave-function renormalization factor. We obtain the fermion's self energy at the one-loop level with a mass-dependent, O(a)O(a) improved action. Numerical results for two interesting special cases, the Wilson and Sheikholeslami-Wohlert actions, are given. The mass dependence of these results smoothly connects the massless and infinite-mass limits, as expected. Combined with Monte Carlo calculations our results can be employed to determine the quark masses in common renormalization schemes.Comment: 33 pages; 11 figures (included

    Statistical investigation of simulated fed intestinal media composition on the equilibrium solubility of oral drugs

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    Gastrointestinal fluid is a complex milieu and it is recognised that gut drug solubility is different to that observed in simple aqueous buffers. Simulated gastrointestinal media have been developed covering fasted and fed states to facilitate in vitro prediction of gut solubility and product dissolution. However, the combination of bile salts, phospholipids, fatty acids and proteins in an aqueous buffered system creates multiple phases and drug solubility is therefore a complex interaction between these components, which may create unique environments for each API. The impact on solubility can be assessed through a statistical design of experiment (DoE) approach, to determine the influence and relationships between factors. In this paper DoE has been applied to fed simulated gastrointestinal media consisting of eight components (pH, bile salt, lecithin, sodium oleate, monoglyceride, buffer, salt and pancreatin) using a two level D-optimal design with forty-four duplicate measurements and four centre points. The equilibrium solubility of a range of poorly soluble acidic (indomethacin, ibuprofen, phenytoin, valsartan, zafirlukast), basic (aprepitant, carvedilol, tadalafil, bromocriptine) and neutral (fenofibrate, felodipine, probucol, itraconazole) drugs was investigated. Results indicate that the DoE provides equilibrium solubility values that are comparable to literature results for other simulated fed gastrointestinal media systems or human intestinal fluid samples. For acidic drugs the influence of pH predominates but other significant factors related to oleate and bile salt or interactions between them are present. For basic drugs pH, oleate and bile salt have equal significance along with interactions between pH and oleate and lecithin and oleate. Neutral drugs show diverse effects of the media components particularly with regard to oleate, bile salt, pH and lecithin but the presence of monoglyceride, pancreatin and buffer have significant but smaller effects on solubility. There are fourteen significant interactions between factors mainly related to the surfactant components and pH, indicating that the solubility of neutral drugs in fed simulated media is complex. The results also indicate that the equilibrium solubility of each drug can exhibit individualistic behaviour associated with the drug’s chemical structure, physicochemical properties and interaction with media components. The utility of DoE for fed simulated media has been demonstrated providing equilibrium solubility values comparable with similar in vitro systems whilst also providing greater information on the influence of media factors and their interactions. The determination of a drug’s gastrointestinal solubility envelope provides useful limits that can potentially be applied to in silico modelling and in vivo experiments

    Lattice Gauge Theory -- Present Status

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    Lattice gauge theory is our primary tool for the study of non-perturbative phenomena in hadronic physics. In addition to giving quantitative information on confinement, the approach is yielding first principles calculations of hadronic spectra and matrix elements. After years of confusion, there has been significant recent progress in understanding issues of chiral symmetry on the lattice. (Talk presented at HADRON 93, Como, Italy, June 1993.)Comment: 11 pages, BNL-4946

    B and D Meson Decay Constants in Lattice QCD

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    We have calculated the decay constants of B and DD mesons with lattice QCD. We use an O(a)O(a) improved action that takes light quark actions as a starting point, tuned so that it can be directly applied at the physical masses of the bb and cc quarks. Our results are f_B = 164 \err{+14}{-11} \pm 8 MeV, f_{B_s} = 185 \err{+13}{-8} \pm 9 MeV, f_D = 194 \err{+14}{-10} \pm 10 MeV, and f_{D_s} = 213 \err{+14}{-11} \pm 11 MeV in the quenched approximation. The first error in each case is statistical, and the second is from perturbation theory. We show that discretization errors are under control in our approach, and smaller than our statistical errors. The effects of the quenched approximation may raise our quenched result by up to 10%.Comment: 21 pages, 6 figure

    Statistical investigation of the full concentration range of fasted and fed simulated intestinal fluid on the equilibrium solubility of oral drugs

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    Upon oral administration the solubility of a drug in intestinal fluid is a key property influencing bioavailability. It is also recognised that simple aqueous solubility does not reflect intestinal solubility and to optimise in vitro investigations simulated intestinal media systems have been developed. Simulated intestinal media which can mimic either the fasted or fed state consists of multiple components each of which either singly or in combination may influence drug solubility, a property that can be investigated by a statistical design of experiment technique. In this study a design of experiment covering the full range from the lower limit of fasted to the upper limit of fed parameters and using a small number of experiments has been performed. The measured equilibrium solubility values are comparable with literature values for simulated fasted and fed intestinal fluids as well as human fasted and fed intestinal fluids. The equilibrium solubility data range is statistically equivalent to a combination of published fasted and fed design of experiment data in six (indomethacin, phenytoin, zafirlukast, carvedilol, fenofibrate and probucol) drugs with three (aprepitant, tadalafil and felodipine) drugs not equivalent. In addition the measured equilibrium solubility data sets were not normally distributed. Further studies will be required to determine the reasons for these results however it implies that a single solubility measurement without knowledge of the solubility distribution will be of limited value. The statistically significant media factors which promote equilibrium solubility (pH, sodium oleate and bile salt) were in agreement with published results but the number of determined significant factors and factor interactions was fewer in this study, lecithin for example did not influence solubility. This may be due to the reduction in statistical sensitivity from the lower number of experimental data points or the fact that using the full range will examine media parameters ratios that are not biorelevant. Overall the approach will provide an estimate of the solubility range and the most important media factors but will not be equivalent to larger scale focussed studies. Further investigations will be required to determine why some drugs do not produce equivalent DoE solubility distributions, for example combined fasted and fed DoE, but this simply may be due to the complexity and individuality of the interactions between a drug and the media components

    Quarkonium mass splittings in three-flavor lattice QCD

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    We report on calculations of the charmonium and bottomonium spectrum in lattice QCD. We use ensembles of gauge fields with three flavors of sea quarks, simulated with the asqtad improved action for staggered fermions. For the heavy quarks we employ the Fermilab interpretation of the clover action for Wilson fermions. These calculations provide a test of lattice QCD, including the theory of discretization errors for heavy quarks. We provide, therefore, a careful discussion of the results in light of the heavy-quark effective Lagrangian. By and large, we find that the computed results are in agreement with experiment, once parametric and discretization errors are taken into account.Comment: 21 pages, 17 figure

    Tadpole renormalization and relativistic corrections in lattice NRQCD

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    We make a comparison of two tadpole renormalization schemes in the context of the quarkonium hyperfine splittings in lattice NRQCD. Improved gauge-field and NRQCD actions are analyzed using the mean-link u0,Lu_{0,L} in Landau gauge, and using the fourth root of the average plaquette u0,Pu_{0,P}. Simulations are done for ccˉc\bar c, bcˉb\bar c, and bbˉb\bar b systems. The hyperfine splittings are computed both at leading and at next-to-leading order in the relativistic expansion. Results are obtained at lattice spacings in the range of about 0.14~fm to 0.38~fm. A number of features emerge, all of which favor tadpole renormalization using u0,Lu_{0,L}. This includes much better scaling behavior of the hyperfine splittings in the three quarkonium systems when u0,Lu_{0,L} is used. We also find that relativistic corrections to the spin splittings are smaller when u0,Lu_{0,L} is used, particularly for the ccˉc\bar c and bcˉb\bar c systems. We also see signs of a breakdown in the NRQCD expansion when the bare quark mass falls below about one in lattice units. Simulations with u0,Lu_{0,L} also appear to be better behaved in this context: the bare quark masses turn out to be larger when u0,Lu_{0,L} is used, compared to when u0,Pu_{0,P} is used on lattices with comparable spacings. These results also demonstrate the need to go beyond tree-level tadpole improvement for precision simulations.Comment: 14 pages, 7 figures (minor changes to some phraseology and references

    Uncertainties in the MSbar bottom quark mass from relativistic sum rules

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    A detailed compilation of uncertainties in the MSbar bottom quark mass m_b(m_b) obtained from low-n spectral sum rules at order alpha_s^2 is given including charm mass effects and secondary b production. The experimental continuum region above 11.1 GeV is treated conservatively. An inconsistency of the PDG averages for the electronic partial widths of Upsilon(4S) and Upsilon(5S) is pointed out. From our analysis we obtain m_b(m_b)=4.20\pm 0.09 GeV. The impact of future CLEO data is discussed.Comment: 11 pages, late
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