367 research outputs found
Search for Lambda^2/p^2 corrections to the QCD running coupling
We investigate the occurrence of power terms in the running
QCD coupling by analysing non-perturbative measurements of at
quite low momenta obtained from the lattice three-gluon vertex. Our study
provides some evidence for such a contribution. The phenomenological
implications of such a presence are reviewed.Comment: 3 pages, 1 figure, LaTeX, LATTICE98(Confinement
Recommended from our members
Intermittent exotropia: are we underminusing by not overminusing?
In this invited commentary, the authors discuss whether the use of minus lenses to aid control of intermittent exotropia has an alternative method of action. Conventional theory suggests that the lenses induce accommodation and therefore accommodative convergence to reduce the angle of deviation. We discuss evidence which suggests that convergence is induced to control the primary deviation and that the minus lenses allow this control by correcting refractive blur caused by additional vergence accommodation
Renormalization-Scale-Invariant PQCD Predictions for R_e+e- and the Bjorken Sum Rule at Next-to-Leading Order
We discuss application of the physical QCD effective charge ,
defined via the heavy-quark potential, in perturbative calculations at
next-to-leading order. When coupled with the Brodsky-Lepage-Mackenzie
prescription for fixing the renormalization scales, the resulting series are
automatically and naturally scale and scheme independent, and represent
unambiguous predictions of perturbative QCD. We consider in detail such
commensurate scale relations for the annihilation ratio
and the Bjorken sum rule. In both cases the improved predictions are in
excellent agreement with experiment.Comment: 13 Latex pages with 5 figures; to be published in Physical Review
Drosophila melanogaster MNK/Chk2 and p53 regulate multiple DNA repair and apoptotic pathways following DNA damage
We have used genetic and microarray analysis to determine how ionizing radiation (IR) induces p53-dependent transcription and apoptosis in Drosophila melanogaster. IR induces MNK/Chk2-dependent phosphorylation of p53 without changing p53 protein levels, indicating that p53 activity can be regulated without an Mdm2-like activity. In a genome-wide analysis of IR-induced transcription in wild-type and mutant embryos, all IR-induced increases in transcript levels required both p53 and the Drosophila Chk2 homolog MNK. Proapoptotic targets of p53 include hid, reaper, sickle, and the tumor necrosis factor family member EIGER: Overexpression of Eiger is sufficient to induce apoptosis, but mutations in Eiger do not block IR-induced apoptosis. Animals heterozygous for deletions that span the reaper, sickle, and hid genes exhibited reduced IR-dependent apoptosis, indicating that this gene complex is haploinsufficient for induction of apoptosis. Among the genes in this region, hid plays a central, dosage-sensitive role in IR-induced apoptosis. p53 and MNK/Chk2 also regulate DNA repair genes, including two components of the nonhomologous end-joining repair pathway, Ku70 and Ku80. Our results indicate that MNK/Chk2-dependent modification of Drosophila p53 activates a global transcriptional response to DNA damage that induces error-prone DNA repair as well as intrinsic and extrinsic apoptosis pathways
A calculation of the Lepage-Mackenzie scale for the lattice axial and vector currents
We calculate the perturbative scales (q*) for the axial and vector currents
for the Wilson action, with and without tadpole improvement, using Lepage and
Mackenzie's formalism. The scale for the pseudoscalar density (times the mass)
is computed as well. Contrary to naive expectation, tadpole improvement reduces
q* by only a small amount for the operators we consider. We also discuss the
use of a nonperturbative coupling to calculate the perturbative scale.Comment: 13 pages. One postscript figur
An estimate of the flavour singlet contributions to the hyperfine splitting in charmonium
We explore the splitting between flavour singlet and non-singlet mesons in
charmonium. This has implications for the hyperfine splitting in charmonium
Heavy-light Mesons and Baryons with b quarks
We present lattice results for the spectrum of mesons containing one heavy
quark and of baryons containing one or two heavy quarks. The calculation is
done in the quenched approximation using the NRQCD formalism for the heavy
quark. We analyze the dependence of the mass splittings on both the heavy and
the light quark masses. Meson P-state fine structure and baryon hyperfine
splittings are resolved for the first time. We fix the b quark mass using both
M_B and M_{\Lambda_b}, and our best estimate is m_b^\MSbar(m_b^\MSbar) =
4.35(10)({}^{-3}_{+2})(10) GeV. The spectrum, obtained by interpolation to m_b,
is compared with the experimental data.Comment: 34 pages, LaTeX, 13 postscript figures, version as publish in Phys.
Rev.
Wide-angle elastic scattering and color randomization
Baryon-baryon elastic scattering is considered in the independent scattering
(Landshoff) mechanism. It is suggested that for scattering at moderate
energies, direct and interchange quark channels contribute with equal color
coefficients because the quark color is randomized by soft gluon exchange
during the hadronization stage. With this assumption, it is shown that the
ratio of cross sections at CM angle
decreases from a high energy value of R_{\pbar p / pp} \approx 1/2.7, down to
R_{\pbar p / pp} \approx 1/28, compatible with experimental data at moderate
energies. This sizable fall in the ratio seems to be characteristic of the
Landshoff mechanism, in which changes at the quark level have a strong effect
precisely because the hadronic process occurs via multiple quark scatterings.
The effect of color randomization on the angular distribution of proton-proton
elastic scattering and the cross section ratio is also discussed.Comment: 18 pages, latex2e, 4 uuencoded figures, include
Mutations in FRMD7, a newly identified member of the FERM family, cause X-linked idiopathic congenital nystagmus.
Idiopathic congenital nystagmus is characterized by involuntary, periodic, predominantly horizontal oscillations of both eyes. We identified 22 mutations in FRMD7 in 26 families with X-linked idiopathic congenital nystagmus. Screening of 42 singleton cases of idiopathic congenital nystagmus (28 male, 14 females) yielded three mutations (7%). We found restricted expression of FRMD7 in human embryonic brain and developing neural retina, suggesting a specific role in the control of eye movement and gaze stability
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