7,407 research outputs found
The Off-forward Quark-Quark Correlation Function
The properties of the non-forward quark-quark correlation function are
examined. We derive constraints on the correlation function from the
transformation properties of the fundamental fields of QCD occurring in its
definition. We further develop a method to construct an ansatz for this
correlator. We present the complete leading order set of generalized parton
distributions in terms of the amplitudes of the ansatz. Finally we conclude
that the number of independent generalized parton helicity changing
distributions is four.Comment: Accepted for publication in Physical Review
Spectral analysis of gluonic pole matrix elements for fragmentation
The non-vanishing of gluonic pole matrix elements can explain the appearance
of single spin asymmetries in high-energy scattering processes. We use a
spectator framework approach to investigate the spectral properties of
quark-quark-gluon correlators and use this to study gluonic pole matrix
elements. Such matrix elements appear in principle both for distribution
functions such as the Sivers function and fragmentation functions such as the
Collins function. We find that for a large class of spectator models, the
contribution of the gluonic pole matrix element in fragmentation functions
vanishes. This outcome is important in the study of universality for
fragmentation functions and confirms findings using a different approach.Comment: 9 pages, 4 figures, added reference
Kinematical contributions to the transverse asymmetry in semi-inclusive DIS
We discuss the contributions of the transverse spin component of the target
to the double-spin asymmetries in semi-inclusive deep inelastic scattering of
longitudinally polarized electrons off longitudinally polarized protons.Comment: LaTeX, 4 pages, 4 figures, uses espcrc1.sty, talk presented at the
European Workshop on the QCD Structure of the Nucleon (QCD-N'02), Ferrara,
Italy, April 3-6, 200
A model independent analysis of gluonic pole matrix elements and universality of TMD fragmentation functions
Gluonic pole matrix elements explain the appearance of single spin
asymmetries (SSA) in high-energy scattering processes. They involve a
combination of operators which are odd under time reversal (T-odd). Such matrix
elements appear in principle both for parton distribution functions and parton
fragmentation functions. We show that for parton fragmentation functions these
gluonic pole matrix elements vanish as a consequence of the analytic structure
of scattering amplitudes in Quantum Chromodynamics. This result is important in
the study of the universality of transverse momentum dependent (TMD)
fragmentation functions.Comment: 5 pages, 5 figures, version to appear in Phys. Rev.
Gluonic Pole Matrix Elements in Spectator Models
We investigate the gluonic pole matrix element contributing to the first
moment of the distribution and fragmentation functions in a spectator
model. By performing a spectral analysis, we find that for a large class of
spectator models, the contribution of gluonic pole matrix elements is non-zero
for the distribution correlators, whereas in fragmentation correlators they
vanish. This outcome is important in the study of universality for
fragmentation functions.Comment: Talk given by A. Mukherjee at Transversity 2008, Ferrara, Ital
Bounds on transverse momentum dependent distribution and fragmentation functions
We give bounds on the distribution and fragmentation functions that appear at
leading order in deep inelastic 1-particle inclusive leptoproduction or in
Drell-Yan processes. These bounds simply follow from positivity of the defining
matrix elements and are an important guidance in estimating the magnitude of
the azimuthal and spin asymmetries in these processes.Comment: 5 pages, Revtex, 3 Postscript figures, version with minor changes, to
be published in Physical Review Letter
Театральний фестиваль аматорських колективів «Блакитна троянда»
3-4 квітня 2009 року в Луцьку відбувся театральний фестиваль аматорських колективів «Блакитна троянда». Організатори – Луцька міська рада, Волинський національний університет імені Лесі Українки та театр-студія «Гармидер»
The evolved circumbinary disk of AC Her: a radiative transfer, interferometric and mineralogical study
We aim to constrain the structure of the circumstellar material around the
post-AGB binary and RV Tauri pulsator AC Her. We want to constrain the spatial
distribution of the amorphous as well as of the crystalline dust. We present
very high-quality mid-IR interferometric data that were obtained with
MIDI/VLTI. We analyse the MIDI data and the full SED, using the MCMax radiative
transfer code, to find a good structure model of AC Her's circumbinary disk. We
include a grain size distribution and midplane settling of dust
self-consistently. The spatial distribution of crystalline forsterite in the
disk is investigated with the mid-IR features, the 69~m band and the
11.3~m signatures in the interferometric data. All the data are well
fitted. The inclination and position angle of the disk are well determined at
i=50+-8 and PA=305+-10. We firmly establish that the inner disk radius is about
an order of magnitude larger than the dust sublimation radius. Significant
grain growth has occurred, with mm-sized grains being settled to the midplane
of the disk. A large dust mass is needed to fit the sub-mm fluxes. By assuming
{\alpha}=0.01, a good fit is obtained with a small grain size power law index
of 3.25, combined with a small gas/dust ratio <10. The resulting gas mass is
compatible with recent estimates employing direct gas diagnostics. The spatial
distribution of the forsterite is different from the amorphous dust, as more
warm forsterite is needed in the surface layers of the inner disk. The disk in
AC Her is very evolved, with its small gas/dust ratio and large inner hole.
Mid-IR interferometry offers unique constraints, complementary to mid-IR
features, for studying the mineralogy in disks. A better uv coverage is needed
to constrain in detail the distribution of the crystalline forsterite in AC
Her, but we find strong similarities with the protoplanetary disk HD100546.Comment: update with final version published in A&
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