25,427 research outputs found
Chiral-Odd and Spin-Dependent Quark Fragmentation Functions and their Applications
We define a number of quark fragmentation functions for spin-0, -1/2 and -1
hadrons, and classify them according to their twist, spin and chirality. As an
example of their applications, we use them to analyze semi-inclusive
deep-inelastic scattering on a transversely polarized nucleon.Comment: 19 pages in Plain TeX, MIT CTP #221
Implications of Color Gauge Symmetry For Nucleon Spin Structure
We study the chromodynamical gauge symmetry in relation to the internal spin
structure of the nucleon. We show that 1) even in the helicity eigenstates the
gauge-dependent spin and orbital angular momentum operators do not have
gauge-independent matrix element; 2) the evolution equations for the gluon spin
take very different forms in the Feynman and axial gauges, but yield the same
leading behavior in the asymptotic limit; 3) the complete evolution of the
gauge-dependent orbital angular momenta appears intractable in the light-cone
gauge. We define a new gluon orbital angular momentum distribution
which {\it is} an experimental observable and has a simple scale evolution.
However, its physical interpretation makes sense only in the light-cone gauge
just like the gluon helicity distribution y.Comment: Minor corrections are made in the tex
Leading Chiral Contributions to the Spin Structure of the Proton
The leading chiral contributions to the quark and gluon components of the
proton spin are calculated using heavy-baryon chiral perturbation theory.
Similar calculations are done for the moments of the generalized parton
distributions relevant to the quark and gluon angular momentum densities. These
results provide useful insight about the role of pions in the spin structure of
the nucleon, and can serve as a guidance for extrapolating lattice QCD
calculations at large quark masses to the chiral limit.Comment: 8 pages, 2 figures; a typo in Ref. 7 correcte
Electronic transport in a Cantor stub waveguide network
We investigate theoretically, the character of electronic eigenstates and
transmission properties of a one dimensional array of stubs with Cantor
geometry. Within the framework of real space re-normalization group (RSRG) and
transfer matrix methods we analyze the resonant transmission and extended
wave-functions in a Cantor array of stubs, which lack translational order.
Apart from resonant states with high transmittance we unravel a whole family of
wave-functions supported by such an array clamped between two-infinite ordered
leads, which have an extended character in the RSRG scheme, but, for such
states the transmission coefficient across the lead-sample-lead structure
decays following a power-law as the system grows in size. This feature is
explained from renormalization group ideas and may lead to the possibility of
trapping of electronic, optical or acoustic waves in such hierarchical
geometries
Off-Forward Parton Distributions in 1+1 Dimensional QCD
We use two-dimensional QCD as a toy laboratory to study off-forward parton
distributions (OFPDs) in a covariant field theory. Exact expressions (to
leading order in ) are presented for OFPDs in this model and are
evaluated for some specific numerical examples. Special emphasis is put on
comparing the and regimes as well as on analyzing the
implications for the light-cone description of form factors.Comment: Revtex, 6 pages, 4 figure
Reactor Fuel Fraction Information on the Antineutrino Anomaly
We analyzed the evolution data of the Daya Bay reactor neutrino experiment in
terms of short-baseline active-sterile neutrino oscillations taking into
account the theoretical uncertainties of the reactor antineutrino fluxes. We
found that oscillations are disfavored at with respect to a
suppression of the reactor antineutrino flux and at
with respect to variations of the and
fluxes. On the other hand, the analysis of the rates of the
short-baseline reactor neutrino experiments favor active-sterile neutrino
oscillations and disfavor the suppression of the flux at
and variations of the and fluxes
at . We also found that both the Daya Bay evolution data and the
global rate data are well-fitted with composite hypotheses including variations
of the or fluxes in addition to
active-sterile neutrino oscillations. A combined analysis of the Daya Bay
evolution data and the global rate data shows a slight preference for
oscillations with respect to variations of the and
fluxes. However, the best fits of the combined data are given
by the composite models, with a preference for the model with an enhancement of
the flux and relatively large oscillations.Comment: 9 page
Positivity Constraints for Spin-Dependent Parton Distributions
We derive new positivity constraints on the spin-dependent structure
functions of the nucleon. These model independent results reduce conside\-rably
their domain of allowed values, in particular for the chiral-odd parton
distribution .Comment: 8 pages,CPT-94/P.3059,LaTex,3 fig available on cpt.univ-mrs.fr
directory pub/preprints/94/fundamental-interactions/94-P.305
Higher moments of nucleon spin structure functions in heavy baryon chiral perturbation theory and in a resonance model
The third moment of the twist-3 part of the nucleon spin structure
function is generalized to arbitrary momentum transfer and is
evaluated in heavy baryon chiral perturbation theory (HBChPT) up to order
and in a unitary isobar model (MAID). We show how to link
as well as higher moments of the nucleon spin structure functions
and to nucleon spin polarizabilities. We compare our results with the
most recent experimental data, and find a good description of these available
data within the unitary isobar model. We proceed to extract the twist-4 matrix
element which appears in the suppressed term in the twist
expansion of the spin structure function for proton and neutron.Comment: 30 pages, 7 figure
Quark fragmentation functions in a diquark model for proton and hyperon production
A simple quark-diquark model for nucleon and structure is used to
calculate leading twist light-cone fragmentation functions for a quark to
inclusively decay into P or . The parameters of the model are
determined by fitting to the known deep-inelastic structure functions of the
nucleon. When evolved from the initial to the final scale, the calculated
fragmentation functions are in remarkable agreement (for ) with those
extracted from partially inclusive and experiments at high
energies. Predictions are made, using no additional parameters, for
longitudinally and transversely polarized quarks to fragment into p or
.Comment: 15 pages, latex, figures may be obtained by writing to
hafsa%png-qau%[email protected]
Helicity-Flip Off-Foward Parton Distributions of the Nucleon
We identify quark and gluon helicity-flip distributions defined between
nucleon states of unequal momenta. The evolution of these distributions with
change of renormalization scale is calculated in the leading-logarithmic
approximation. The helicity-flip gluon distributions do not mix with any quark
distribution and are thus a unique signature of gluons in the nucleon. Their
contribution to the generalized virtual Compton process is obtained both in the
form of a factorization theorem and an operator product expansion. In deeply
virtual Compton scattering, they can be probed through distinct angular
dependence of the cross section.Comment: a few corrections made, references change
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