1,947 research outputs found
Angular reduction in multiparticle matrix elements
A general method for the reduction of coupled spherical harmonic products is
presented. When the total angular coupling is zero, the reduction leads to an
explicitly real expression in the scalar products within the unit vector
arguments of the spherical harmonics. For non-scalar couplings, the reduction
gives Cartesian tensor forms for the spherical harmonic products, with tensors
built from the physical vectors in the original expression. The reduction for
arbitrary couplings is given in closed form, making it amenable to symbolic
manipulation on a computer. The final expressions do not depend on a special
choice of coordinate axes, nor do they contain azimuthal quantum number
summations, nor do they have complex tensor terms for couplings to a scalar.
Consequently, they are easily interpretable from the properties of the physical
vectors they contain.Comment: This version contains added comments and typographical corrections to
the original article. Now 27 pages, 0 figure
Multiloop String-Like Formulas for QED
Multiloop gauge-theory amplitudes written in the Feynman-parameter
representation are poised to take advantage of two important developments of
the last decade: the spinor-helicity technique and the superstring
reorganization. The former has been considered in a previous article; the
latter will be elaborated in this paper. We show here how to write multiloop
string-like formulas in the Feynman-parameter representation for any process in
QED, including those involving other non-electromagnetic interactions. The
general connection between the Feynman-parameter approach and the
superstring/first-quantized approach is discussed. In the special case of a
one-loop multi-photon amplitude, these formulas reduce to the ones obtained by
the superstring and the first quantized methods. The string-like formulas
exhibits a simple gauge structure which makes the Ward-Takahashi identity
apparent, and enables the integration-by-parts technique of Bern and Kosower to
be applied, so that gauge-invariant parts can be extracted diagram-by-diagram
with the seagull vertex neglected.Comment: 25 pages in Plain Tex, plus four figures in a postscript file;
McGill/92-5
Identifying risk and mitigating gambling-related harm in online poker
The present paper conducts a critical analysis of the potential for gambling-related harm in relation to online poker participation, and a theoretical evaluation of current responsible gambling strategies employed to mitigate harm in online gambling and applies the evaluation of these strategies specifically to online poker gambling. Theoretically, the primary risk for harm in online poker is the rapid and continuous nature of poker provisions online, and has been demonstrated to be associated with disordered gambling behaviour, including the chasing of monetary losses. The following responsible gambling features were deemed relevant for consideration: informed player choice, voluntary self-exclusion, employee intervention, pre-commitment, in-game feedback, behavioural tracking tools, and age restriction and verification. Although current responsible gambling features are evaluated as theoretically robust, there remains a fundamental need for experimental validation of their effectiveness. Furthermore, despite online poker gamblers perceiving the responsible gambling features as valuable tools, in reality very few players regularly use available responsible gambling features. Ultimately, for the online poker gambling industry to retain market credibility and avoid substantial top-down regulation, it is imperative to demonstrate effectiveness of responsible gambling approaches, and increase customer utilisation of available harm-mitigation features
General Solutions for Tunneling of Scalar Fields with Quartic Potentials in de Sitter Space
The tunneling rates for scalar fields with quartic potentials in de Sitter
space in the limit of no gravitational back reaction are calculated numerically
and the results are fitted by analytic formulae.Comment: (Contours in Figure 1 corrected, two-dimensional fitting coefficient
corrected, references added.), 16 pages, KUNS 124
Complete Equivalence Between Gluon Tree Amplitudes in Twistor String Theory and in Gauge Theory
The gluon tree amplitudes of open twistor string theory, defined as contour
integrals over the ACCK link variables, are shown to satisfy the BCFW
relations, thus confirming that they coincide with the corresponding amplitudes
in gauge field theory. In this approach, the integration contours are specified
as encircling the zeros of certain constraint functions that force the
appropriate relation between the link variables and the twistor string
world-sheet variables. To do this, methods for calculating the tree amplitudes
using link variables are developed further including diagrammatic methods for
organizing and performing the calculations.Comment: 38 page
Multigluon tree amplitudes with a pair of massive fermions
We consider the calculation of n-point multigluon tree amplitudes with a pair
of massive fermions in QCD. We give the explicit transformation rules of this
kind of massive fermion-pair amplitudes with respect to different reference
momenta and check the correctness of them by SUSY Ward identities. Using these
rules and onshell BCFW recursion relation, we calculate the analytic results of
several n-point multigluon amplitudes.Comment: 15page
QCD Corrections to Spin Correlations in Top Quark Production at Lepton Colliders
Spin correlations, using a generic spin basis, are investigated to leading
order in QCD for top quark production at lepton colliders. Even though, these
radiative corrections induce an anomalous gamma/Z magnetic moment for the top
quarks and allow for single, real gluon emission, their effects on the top
quark spin orientation are very small. The final results are that the top (or
anti-top) quarks are produced in an essentially unique spin configuration in
polarized lepton collisions even after including the O(alpha_{s}) QCD
corrections.Comment: 32 pages, REVTeX, 13 Postscript figures, psfig.sty and here.sty are
required. Several references added, Tables 3, 4 and 5 are change
Validation of the reasons for gambling questionnaire (RGQ) in a British population survey
Introduction. The aim of the study is to validate the five-dimensional structure of the Reasons for Gambling Questionnaire (RGQ) and to test the differences between different types of gamblers (i.e., offline gamblers who gambled in-person only vs.mixed-mode gamblers who gambled both online and offline) on the five dimensions of the RGQ. Methods. Data from the 2010 British Gambling Prevalence Survey (BGPS) were used. The analysed data comprised 5,677 individuals (52.7% female; mean age=47.64 years; SD=17.82). Confirmatory factor analysis and independent-samples t-tests were applied. Results. The five-dimensional structure of the RGQ wasconfirmed in the general sample and among gender and age subgroups. Furthermore, mixed-mode gamblers (MMGs) who gambled both online and offline had higher scores for enhancement, recreation and money motives than offline gamblers that gambled in-person only (IPGs). In addition among males, there was a significant difference in the scores for enhancement and recreation motives across MMGs and IPGs. Among past-year gamblers aged 16-34 years, MMGs had higher scores for enhancement, recreational and monetary motives than IPGs whilst among past-year gamblers aged 35-55years, MMGs had higher scores for enhancement and recreational motives than IPGs. Conclusions. The results are consistent with a previous test of the RGQ and the findings indicate that the RGQis a valid instrument to assess gambling motives among the general population
Angular Correlations in Top Quark Pair Production and Decay at Hadron Colliders
We show how to observe sizable angular correlations between the decay
products of the top quark and those of the anti-top quark in top quark pair
production and decay at hadron colliders. These correlations result from the
large asymmetry in the rate for producing like-spin versus unlike-spin top
quark pairs provided the appropriate spin axes are used. The effects of new
physics at production or decay on these correlations are briefly discussed.Comment: 34 pages, revtex, including 12 uuencoded postscript figure
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