2,658 research outputs found
Moments of generalized parton distribution functions and the nucleon spin contents
It is shown that, based only on two empirically known facts besides two
reasonable theoretical postulates, we are inevitably led to a conclusion that
the quark orbital angular momentum carries nearly half of the total nucleon
spin. We also perform a model analysis to find that the quark spin fraction
is extremely sensitive to the pion mass, which may resolve the
discrepancy between the observation and the prediction of the recent lattice
QCD simulation carried out in the heavy pion region.Comment: LaTeX, 8 pages, 1 figur
Chiral odd GPDs in transverse and longitudinal impact parameter spaces
We investigate the chiral odd generalized parton distributions (GPDs) for
non-zero skewness in transverse and longitudinal position spaces by
taking Fourier transform with respect to the transverse and longitudinal
momentum transfer respectively. We present overlap formulas for the chiral-odd
GPDs in terms of light-front wave functions (LFWFs) of the proton both in the
ERBL and DGLAP regions. We calculate them in a field theory inspired model of a
relativistic spin 1/2 composite state with the correct correlation between the
different LFWFs in Fock space, namely that of the quantum fluctuations of an
electron in a generalized form of QED. We show the spin-orbit correlation
effect of the two-particle LFWF as well as the correlation between the
constituent spin and the transverse spin of the target.Comment: 1 figure and references added, typos corrected. version to appear in
Phys.Rev.
Dynamical Polarizabilities of SU(3) Octet of Baryons
We present calculations and an analysis of the spin-independent dipole
electric and magnetic dynamical polarizabilities for the lowest in mass SU(3)
octet of baryons. These extensive calculations are made possible by the recent
implementation of semi-automatized calculations in Chiral Perturbation Theory
which allows evaluating dynamical spin-independent electromagnetic
polarizabilities from Compton scattering up to next-to-the-leading order. Our
results are in good agreement with calculations performed for nucleons found in
the literature. The dependencies for the range of photon energies up to 1 GeV,
covering the majority of the meson photo production channels, are analyzed. The
separate contributions into polarizabilities from the various baryon meson
clouds are studied.Comment: 10 pages, 7 figures, extended analysis of hyperon polarizabilitie
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
Factorization Structure of Gauge Theory Amplitudes and Application to Hard Scattering Processes at the LHC
Previous work on electroweak radiative corrections to high energy scattering
using soft-collinear effective theory (SCET) has been extended to include
external transverse and longitudinal gauge bosons and Higgs bosons. This allows
one to compute radiative corrections to all parton-level hard scattering
amplitudes in the standard model to NLL order, including QCD and electroweak
radiative corrections, mass effects, and Higgs exchange corrections, if the
high-scale matching, which is suppressed by two orders in the log counting, and
contains no large logs, is known. The factorization structure of the effective
theory places strong constraints on the form of gauge theory amplitudes at high
energy for massless and massive gauge theories, which are discussed in detail
in the paper. The radiative corrections can be written as the sum of
process-independent one-particle collinear functions, and a universal soft
function. We give plots for the radiative corrections to q qbar -> W_T W_T, Z_T
Z_T, W_L W_L, and Z_L H, and gg -> W_T W_T to illustrate our results. The
purely electroweak corrections are large, ranging from 12% at 500 GeV to 37% at
2 TeV for transverse W pair production, and increasing rapidly with energy. The
estimated theoretical uncertainty to the partonic (hard) cross-section in most
cases is below one percent, smaller than uncertainties in the parton
distribution functions (PDFs). We discuss the relation between SCET and other
factorization methods, and derive the Magnea-Sterman equations for the Sudakov
form factor using SCET, for massless and massive gauge theories, and for light
and heavy external particles.Comment: 44 pages, 30 figures. Refs added, typos fixed. ZL ZL plots removed
because of a possible subtlet
QCD Flux Tubes as Sigma Model Relics
We describe flux tubes and their interactions in a low energy sigma model
induced by SU(\NF) \goto SO(\NF) flavor symmetry breaking in QCD.
Gauge confinement manifests itself in the low energy theory through flux tube
interactions with unscreened sources. The flux tubes which mediate confinement
also illustrate an interesting ambiguity in defining global Alice strings.Comment: 12 pages (REVTEX) plus one figur
Model Independent Results for Heavy Quarkonium
We review a number of results for the spectrum and inclusive decays of heavy
quarkonium systems which can be derived from QCD under well controlled
approximations. They essentially follow from the hierarchy of scales in these
systems, which can be efficiently exploited using non-relativistic effective
field theories. In particular, we discuss under which conditions
non-relativistic potential models emerge as effective theories of QCD.Comment: 15 pages. Invited brief revie
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