An important unresolved question in strong interaction physics concerns the parameterization of power-suppressed long-distance effects to hard processes that do not admit an operator product expansion (OPE). Recently Bauer et al. have developed an effective field theory framework that allows one to formulate the problem of soft-collinear factorization in terms of fields and operators. We extend the formulation of soft-collinear effective theory, previously worked out to leading order, to second order in a power series in the inverse of the hard scale. We give the effective Lagrangian and the expansion of "currents" that produce collinear particles in heavy quark decay. This is the first step towards a theory of power corrections to hard processes where the OPE cannot be used. We apply this framework to heavy-to-light meson transition form factors at large recoil energy.
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In this paper we study the non-factorizable QED corrections to
W-pair-mediated (charged-current) four-fermion production in electron-positron
collisions. A brief account of the obtained analytical results is given. They
turn out to be different from the ones published in the literature. For the
first time numerical results are presented, in particular the effects on the W
line-shape. These effects are of the order of a per cent. Applying the same
methods to ZZ- or ZH-mediated four-fermion production, the non-factorizable
$O(\alpha)$ corrections to the Z or H line-shape vanish.Comment: 11 pages, LaTeX2e, 2 figures, uses axodraw.st
Radiative corrections to processes that involve the production and subsequent decay of unstable particles are complex due to various theoretical and practical problems. The so-called double-pole approximation offers a way out of these problems. This method is applied to the reaction e + e − → W + W − → 4 fermions, which allows us to address all the key issues of dealing with unstable particles, like gauge invariance, interactions between different stages of the reaction, and overlapping resonances. Within the double-pole approximation the complete O(α) electroweak corrections are evaluated for this off-shell W -pair production process. Examples of the effect of these corrections on a number of distributions are presented. These comprise mass and angular distributions as well as the photon-energy spectrum.
Tests of the standard model and its hypothetical extensions require precise
theoretical predictions for processes involving massive, unstable particles. It
is well-known that ordinary weak-coupling perturbation theory breaks down due
to intermediate singular propagators. Various pragmatic approaches have been
developed to deal with this difficulty. In this paper we construct an effective
field theory for resonant processes utilizing the hierarchy of scales between
the mass of the unstable particle, M, and its width, Gamma. The effective
theory allows calculations to be systematically arranged into a series in g^2
and Gamma/M, and preserves gauge invariance in every step. We demonstrate the
applicability of this method by calculating explicitly the inclusive line shape
of a scalar resonance in an abelian gauge-Yukawa model at next-to-leading order
in Gamma/M and the weak couplings. We also discuss the extension to
next-to-next-to-leading order and compute an interesting subset of these
corrections.Comment: 45 page
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