28,185 research outputs found
k_T factorization is violated in production of high-transverse-momentum particles in hadron-hadron collisions
We show that hard-scattering factorization is violated in the production of
high-p_T hadrons in hadron-hadron collisions, in the case that the hadrons are
back-to-back, so that k_T factorization is to be used. The explicit
counterexample that we construct is for the single-spin asymmetry with one beam
transversely polarized. The Sivers function needed here has particular
sensitivity to the Wilson lines in the parton densities. We use a greatly
simplified model theory to make the breakdown of factorization easy to check
explicitly. But the counterexample implies that standard arguments for
factorization fail not just for the single-spin asymmetry but for the
unpolarized cross section for back-to-back hadron production in QCD in
hadron-hadron collisions. This is unlike corresponding cases in e^+e^-
annihilation, Drell-Yan, and deeply inelastic scattering. Moreover, the result
endangers factorization for more general hadroproduction processes.Comment: 10 pages. V. 2: Title change, misprints and minor corrections, as in
journal versio
QCD Factorization for Semi-Inclusive Deep-Inelastic Scattering at Low Transverse Momentum
We demonstrate a factorization formula for semi-inclusive deep-inelastic
scattering with hadrons in the current fragmentation region detected at low
transverse momentum. To facilitate the factorization, we introduce the
transverse-momentum dependent parton distributions and fragmentation functions
with gauge links slightly off the light-cone, and with soft-gluon radiations
subtracted. We verify the factorization to one-loop order in perturbative
quantum chromodynamics and argue that it is valid to all orders in perturbation
theory.Comment: 28 pages, figures include
A QCD Analysis of Double Parton Scattering: Color Correlations, Interference Effects and Evolution
We derive a factorization formula for the double Drell-Yan cross section in
terms of double parton distribution functions (dPDFs). Diparton flavor, spin
and color correlations and parton-exchange interference terms contribute, even
for unpolarized beams. Soft radiation effects are nontrivial for the color
correlation and interference contributions, and are described by
non-perturbative soft functions. We provide a field-theoretic definition of the
quark dPDFs and study some of their basic properties, including discrete
symmetries and their interpretation in a non-relativistic quark model. We
calculate the renormalization group evolution of the quark dPDFs and of the
soft functions. The evolution receives contributions from both ultraviolet and
rapidity divergences. We find that color correlation and interference effects
are Sudakov suppressed, greatly reducing the number of dPDFs needed to describe
double parton scattering at high energy experiments.Comment: 24 pages, 15 figures, v2: added WW cross section, additional spin
structures, finite terms of one-loop soft function, journal versio
The Zero-Bin and Mode Factorization in Quantum Field Theory
We study a Lagrangian formalism that avoids double counting in effective
field theories where distinct fields are used to describe different infrared
momentum regions for the same particle. The formalism leads to extra
subtractions in certain diagrams and to a new way of thinking about
factorization of modes in quantum field theory. In non-relativistic field
theories, the subtractions remove unphysical pinch singularities in box type
diagrams, and give a derivation of the known pull-up mechanism between soft and
ultrasoft fields which is required by the renormalization group evolution. In a
field theory for energetic particles, the soft-collinear effective theory
(SCET), the subtractions allow the theory to be defined with different infrared
and ultraviolet regulators, remove double counting between soft, ultrasoft, and
collinear modes, and give results which reproduce the infrared divergences of
the full theory. Our analysis shows that convolution divergences in
factorization formul\ae occur due to an overlap of momentum regions. We propose
a method that avoids this double counting, which helps to resolve a long
standing puzzle with singularities in collinear factorization in QCD. The
analysis gives evidence for a factorization in rapidity space in exclusive
decays.Comment: 92 pages, v4- Journal version. Some improvements to language in
sections I, IIA, VI
Gravireggeons and transplanckian scattering in models with one extra dimension
The inelastic scattering of the brane fields induced by -channel
gravireggeons exchanges in the RS model with a small curvature is
considered, and the imaginary part of the eikonal is analytically calculated.
It is demonstrated that the results can be obtained from the corresponding
formulae previously derived in the ADD model with one extra dimension of the
size by formal replacement . The inelastic
cross section for the scattering of ultra-high neutrino off the nucleon is
numerically estimated for the case TeV, where
is a reduced Planck scale in five warped dimensions.Comment: 17 pages, LaTeX2e, 3 eps figure
A Pinned Polymer Model of Posture Control
A phenomenological model of human posture control is posited. The dynamics
are modelled as an elastically pinned polymer under the influence of noise. The
model accurately reproduces the two-point correlation functions of experimental
posture data and makes predictions for the response function of the postural
control system. The physiological and clinical significance of the model is
discussed.Comment: uuencoded post script file, 17 pages with 3 figure
Hadronic Dijet Imbalance and Transverse-Momentum Dependent Parton Distributions
We compare several recent theoretical studies of the single transverse spin
asymmetry in dijet-correlations at hadron colliders. We show that the results
of these studies are all consistent. To establish this, we investigate in
particular the two-gluon exchange contributions to the relevant initial and
final state interactions in the context of a simplifying model. Overall, the
results confirm that the dijet imbalance obeys at best a non-standard or
"generalized" transverse-momentum-dependent factorization.Comment: 13 pages, 3 figure
Hard-scattering factorization with heavy quarks: A general treatment
A detailed proof of hard scattering factorization is given with the inclusion
of heavy quark masses. Although the proof is explicitly given for
deep-inelastic scattering, the methods apply more generally The
power-suppressed corrections to the factorization formula are uniformly
suppressed by a power of \Lambda/Q, independently of the size of heavy quark
masses, M, relative to Q.Comment: 52 pages. Version as published plus correction of misprint in Eq.
(45
A New Look at Azimuthal Wave Propagation Constants of an n-Layered Dielectric Coated PEC Cylinder
A method for determining the azimuthal wave propagation constants supported by an n-layered dielectric coated PEC cylinder is presented. The method, based on a Green\u27s function described in , is designed to optimally handle layered cylinders where the number of layers is extremely large as might be encountered in structures designed using transformational optics. The method is also tractable for any stratification profile without the need for individual layer analysis. We implement a recently developed numerical method to calculate Bessel functions of complex order and argument. Our method is verified by comparison with previously published results. We also present new results for a 5-layer case demonstrating self consistency and improved accuracy over published methods. Finally, to illustrate the method\u27s benefits, we present a brief analysis of two multilayer structures; a multilayer variation of the coated cylinder presented in and an example of a 7-layer case that approximates a material parameter gradient
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