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466 results on '"Sharkey, K A"'

3. Is the up-quark massless?

Author

UKQCD Collaboration, Irving, A. C., McNeile, C., Michael, C., Sharkey, K. J., and Wittig, H.

Subjects
High Energy Physics - Lattice, High Energy Physics - Phenomenology, Nuclear Theory
Abstract

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

Published
2001
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4. Effects of non-perturbatively improved dynamical fermions in QCD at fixed lattice spacing

Author

UKQCD Collaboration, Allton, C. R., Booth, S. P., Bowler, K. C., Garden, J., Hart, A., Hepburn, D., Irving, A. C., Joo, B., Kenway, R. D., Maynard, C. M., McNeile, C., Michael, C., Pickles, S. M., Sexton, J. C., Sharkey, K. J., Sroczynski, Z., Talevi, M., Teper, M., and Wittig, H.

Subjects
High Energy Physics - Lattice
Abstract

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

Published
2001
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5. The flavour singlet mesons in QCD

Author

UKQCD Collaboration, McNeile, C., Michael, C., and Sharkey, K. J.

Subjects
High Energy Physics - Lattice
Abstract

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

Published
2001
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6. Lattice calculation of $1/p^2$ corrections to $\alpha_s$ and of $\Lambda_{\rm {QCD}}$ in the $\widetilde{MOM}$ scheme

Author

Boucaud, Ph., Burgio, G., Di Renzo, F., Leroy, J. P., Micheli, J., Parrinello, C., Pène, O., Pittori, C., Rodríguez-Quintero, J., Roiesnel, C., and Sharkey, K.

Subjects
High Energy Physics - Phenomenology, High Energy Physics - Lattice
Abstract

We report on very strong evidence of the occurrence of power terms in $\as(p)$, the QCD running coupling constant in the $\widetilde{MOM}$ scheme, by analyzing non-perturbative measurements from the lattice three-gluon vertex between 2.0 and 10.0 GeV at zero flavor. While putting forward the caveat that this definition of the coupling is a gauge dependent one, the general relevance of such an occurrence is discussed. We fit $\Lambda_{\bar{\rm MS}}^{(n_f=0)}= 237 \pm 3 ^{+ 0}_{-10}$ MeV in perfect agreement with the result obtained by the ALPHA group with a totally different method. The power correction to $\as(p)$ is fitted to $(0.63\pm 0.03 ^{+ 0.0}_{- 0.13}) {\rm GeV}^2/p^2$., Comment: 21 pages, 3 figures

Published
2000
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7. An adenoviral-vectored vaccine confers seroprotection against capsular group B meningococcal disease

Author

Dold, C, Marsay, L, Wang, N, Silva-Reyes, L, Clutterbuck, E, Paterson, GK, Sharkey, K, Wyllie, D, Beernink, PT, Hill, AV, Pollard, AJ, and Rollier, CS

Abstract

Adenoviral-vectored vaccines are licensed for prevention of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Ebola virus, but, for bacterial proteins, expression in a eukaryotic cell may affect the antigen's localization and conformation or lead to unwanted glycosylation. Here, we investigated the potential use of an adenoviral-vectored vaccine platform for capsular group B meningococcus (MenB). Vector-based candidate vaccines expressing MenB antigen factor H binding protein (fHbp) were generated, and immunogenicity was assessed in mouse models, including the functional antibody response by serum bactericidal assay (SBA) using human complement. All adenovirus-based vaccine candidates induced high antigen-specific antibody and T cell responses. A single dose induced functional serum bactericidal responses with titers superior or equal to those induced by two doses of protein-based comparators, as well as longer persistence and a similar breadth. The fHbp transgene was further optimized for human use by incorporating a mutation abrogating binding to the human complement inhibitor factor H. The resulting vaccine candidate induced high and persistent SBA responses in transgenic mice expressing human factor H. The optimized transgene was inserted into the clinically relevant ChAdOx1 backbone, and this vaccine has now progressed to clinical development. The results of this preclinical vaccine development study underline the potential of vaccines based on genetic material to induce functional antibody responses against bacterial outer membrane proteins.

Published
2023

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