1,559 research outputs found
Calculating loops without loop calculations: NLO computation of pentaquark correlators
We compute next-to-leading order (NLO) perturbative QCD corrections to the
correlators of interpolating pentaquark currents. We employ modular techniques
in configuration space which saves us from the onus of having to do loop
calculations. The modular technique is explained in some detail. We present
explicit NLO results for several interpolating pentaquark currents that have
been written down in the literature. Our modular approach is easily adapted to
the case of NLO corrections to multiquark correlators with an arbitrary number
of quarks/antiquarks.Comment: 23 pages, 1 figure, published version. arXiv admin note: text overlap
with arXiv:hep-lat/031001
Renormalization schemes and renormalons
We describe some ways how higher order corrections can reveal themselves if
integrated over the infrared region. We show that in different renormalization
group (RG) schemes and for some observables one has no factorial divergences.
We argue that for treating things in the infrared region it is preferable to
start with a RG scheme without the infrared Landau pole in the running coupling
constant. The uncertainties for the lepton width resulting from
accounting for higher order corrections are discussed.Comment: Latex, 18 pages, two table
Absorption in Ultra-Peripheral Nucleus-Atom Collisions in Crystal
The Glauber theory description of particle- and nucleus-crystal Coulomb
interactions at high-energy is developed. The allowance for the lattice thermal
vibrations is shown to produce strong absorption effect which is of prime
importance for quantitative understanding of the coherent Coulomb excitation of
ultra-relativistic particles and nuclei passing through the crystal.Comment: 8 pages, LaTe
Landau equations and asymptotic operation
The pinched/non-pinched classification of intersections of causal
singularities of propagators in Minkowski space is reconsidered in the context
of the theory of asymptotic operation as a first step towards extension of the
latter to non-Euclidean asymptotic regimes. A highly visual
distribution-theoretic technique of singular wave fronts is tailored to the
needs of the theory of Feynman diagrams. Besides a simple derivation of the
usual Landau equations in the case of the conventional singularities, the
technique naturally extends to other types of singularities e.g. due to linear
denominators in non-covariant gauges etc. As another application, the results
of Euclidean asymptotic operation are extended to a class of quasi-Euclidean
asymptotic regimes in Minkowski space.Comment: 15p PS (GSview), IJMP-A (accepted
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