Generalized Background-Field Method

The graphical method discussed previously can be used to create new gauges not reachable by the path-integral formalism. By this means a new gauge is designed for more efficient two-loop QCD calculations. It is related to but simpler than the ordinary background-field gauge, in that even the triple-gluon vertices for internal lines contain only four terms, not the usual six. This reduction simplifies the calculation inspite of the necessity to include other vertices for compensation. Like the ordinary background-field gauge, this generalized background-field gauge also preserves gauge invariance of the external particles. As a check of the result and an illustration for the reduction in labour, an explicit calculation of the two-loop QCD $\beta$-function is carried out in this new gauge. It results in a saving of 45% of computation compared to the ordinary background-field gauge.Comment: 17 pages, Latex, 18 figures in Postscrip

Small-Recoil Approximation

In this review we discuss a technique to compute and to sum a class of Feynman diagrams, and some of its applications. These are diagrams containing one or more energetic particles that suffer very little recoil in their interactions. When recoil is completely neglected, a decomposition formula can be proven. This formula is a generalization of the well-known eikonal formula, to non-abelian interactions. It expresses the amplitude as a sum of products of irreducible amplitudes, with each irreducible amplitude being the amplitude to emit one, or several mutually interacting, quasi-particles. For abelian interaction a quasi-particle is nothing but the original boson, so this decomposition formula reduces to the eikonal formula. In non-abelian situations each quasi-particle can be made up of many bosons, though always with a total quantum number identical to that of a single boson. This decomposition enables certain amplitudes of all orders to be summed up into an exponential form, and it allows subleading contributions of a certain kind, which is difficult to reach in the usual way, to be computed. For bosonic emissions from a heavy source with many constituents, a quasi-particle amplitude turns out to be an amplitude in which all bosons are emitted from the same constituent. For high-energy parton-parton scattering in the near-forward direction, the quasi-particle turns out to be the Reggeon, and this formalism shows clearly why gluons reggeize but photons do not. The ablility to compute subleading terms in this formalism allows the BFKL-Pomeron amplitude to be extrapolated to asymptotic energies, in a unitary way preserving the Froissart bound. We also consider recoil corrections for abelian interactions in order to accommodate the Landau-Pomeranchuk-Migdal effect.Comment: 21 pages with 4 figure

Novel Bose-Einstein Interference in the Passage of a Fast Particle in a Dense Medium

When an energetic particle collides coherently with many medium particles at high energies, the Bose-Einstein symmetry with respect to the interchange of the exchanged virtual bosons leads to a destructive interference of the Feynman amplitudes in most regions of the phase space but a constructive interference in some other regions of the phase space. As a consequence, the recoiling medium particles have a tendency to come out collectively along the direction of the incident fast particle, each carrying a substantial fraction of the incident longitudinal momentum. Such an interference appearing as collective recoils of scatterers along the incident particle direction may have been observed in angular correlations of hadrons associated with a high-$p_T$ trigger in high-energy AuAu collisions at RHIC.Comment: 10 pages, 2 figures, invited talk presented at the 35th Symposium on Nuclear Physics, Cocoyoc, Mexico, January 3, 2012, to be published in IOP Conference Serie

How well does the index of receptivity to tobacco industry promotion discriminate between smoking and never smoking adolescents.

Tobacco advertising is often named as the culprit that causes children to start smoking (Lancaster &amp; Lancaster, 2003). This belief can partly be attributed to the Index of Receptivity to Tobacco Industry Promotion (IRTIP) developed by Evans, Farkas, Gilpin, Berry, &amp; Pierce (1995). IRTIP was later modified and used by Pierce, Choi, Gilpin, Farkas, &amp; Berry (1998) in a longitudinal study that claimed to have found a causal link between advertising and adolescent cigarette trial. The model is advertised by the American National Cancer Institute (2004) as being able to measure the likelihood of an adolescent starting smoking. Because of Pierce&rsquo;s causality claim and this endorsement, IRTIP has been widely adopted by tobacco-control researchers. Consequently, the results from IRTIP based surveys have played a central role in influencing tobacco control policy. Based on the logic that a model used to predict the chances of a non-smoker becoming a smoker should be able to distinguish between these two groups, discriminant analysis with dummy coded variables was used to validate IRTIP. The results show that while IRTIP classifies never-smokers well, it grossly misclassifies smokers. This leads to questions about the validity of the model and of studies using IRTIP.<br /

The influence of cultural values on brand loyalty

It is well documented that culture can influence consumer attitudes and behavior. While there have been numerous studies on how culture influences the four Ps of the marketing mix, few researchers have examined its effect on customer loyalty. More specifically, how consumers who identify more with certain cultural traits are likely to be more brand loyal. Using Hofstede&rsquo;s cultural dimensions, this study empirically examines cultural effects on consumer-reported &ldquo;proneness&rdquo; to brand loyalty and finds that those who scored highly in individualism and uncertainty avoidance have greater affinity for exhibiting loyalty to a brand.<br /

Sound fields near building facades: comparison of finite and semi-infinite reflectors on a rigid ground plane

The sound field in front of, and close to a building facade is relevant to the measurement and prediction of environmental noise and sound insulation. For simplicity it is often assumed that the facade can be treated as a semi-infinite reflector, however in the low-frequency range (50–200 Hz) this is no longer appropriate as the wavelengths are similar or larger than the facade dimensions. Scale model measurements and predictions using integral equation methods have been used to investigate the effect of diffraction on the sound field in front of finite size reflectors. For the situation that is commonly encountered in front of building facades, the results indicate that diffraction effects are only likely to be significant in the low-frequency range (50–200 Hz) when the façade dimensions are less than 5 m. This assumes that there is a point source close to the ground and microphones at a height of 1.2 or 1.5 m, at a distance between 1 and 2 m in front of the façade. © 2008 Elsevier Ltd. All rights reserved