22,707 research outputs found
Counting Form Factors of Twist-Two Operators
We present a simple method to count the number of hadronic form factors based
on the partial wave formalism and crossing symmetry. In particular, we show
that the number of independent nucleon form factors of spin-n, twist-2
operators (the vector current and energy-momentum tensor being special
examples) is n+1. These generalized form factors define the generalized
(off-forward) parton distributions that have been studied extensively in the
recent literature. In proving this result, we also show how the J^{PC} rules
for onium states arise in the helicity formalism.Comment: 7 pages, LaTeX (revtex
Orbital Angular Momentum in Scalar Diquark Model and QED
We compare the orbital angular momentum of the 'quark' in the scalar diquark
model as well as that of the electron in QED (to order {\alpha}) obtained from
the Jaffe-Manohar de- composition to that obtained from the Ji relation. We
estimate the importance of the vector potential in the definition of orbital
angular momentum
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
Lorentz Symmetry and the Internal Structure of the Nucleon
To investigate the internal structure of the nucleon, it is useful to
introduce quantities that do not transform properly under Lorentz symmetry,
such as the four-momentum of the quarks in the nucleon, the amount of the
nucleon spin contributed by quark spin, etc. In this paper, we discuss to what
extent these quantities do provide Lorentz-invariant descriptions of the
nucleon structure.Comment: 6 pages, no figur
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
Multivariate adaptive regression splines for estimating riverine constituent concentrations
Regression-based methods are commonly used for riverine constituent concentration/flux estimation, which is essential for guiding water quality protection practices and environmental decision making. This paper developed a multivariate adaptive regression splines model for estimating riverine constituent concentrations (MARS-EC). The process, interpretability and flexibility of the MARS-EC modelling approach, was demonstrated for total nitrogen in the Patuxent River, a major river input to Chesapeake Bay. Model accuracy and uncertainty of the MARS-EC approach was further analysed using nitrate plus nitrite datasets from eight tributary rivers to Chesapeake Bay. Results showed that the MARS-EC approach integrated the advantages of both parametric and nonparametric regression methods, and model accuracy was demonstrated to be superior to the traditionally used ESTIMATOR model. MARS-EC is flexible and allows consideration of auxiliary variables; the variables and interactions can be selected automatically. MARS-EC does not constrain concentration-predictor curves to be constant but rather is able to identify shifts in these curves from mathematical expressions and visual graphics. The MARS-EC approach provides an effective and complementary tool along with existing approaches for estimating riverine constituent concentrations
Non-Abelian Medium Effects in Quark-Gluon Plasma
Based on the kinetic theory, the non-Abelian medium property of hot
Quark-Gluon Plasma is investigated. The nonlinearity of the plasma comes from
two aspects: The nonlinear wave-wave interaction and self-interaction of color
field. The non-Abelian color permittivity is obtained by expanding the kinetic
equations to third order. As an application, the nonlinear Landau damping rate
and the nonlinear eigenfrequency shift are calculated in the longwave length
limit.Comment: 12 pages(Revtex), no figure
Pion production in deeply virtual Compton scattering
Using a soft pion theorem based on chiral symmetry and a
resonance model we propose an estimate for the production cross section of low
energy pions in the deeply virtual Compton scattering (DVCS) process. In
particular, we express the processes in terms of
generalized parton distributions. We provide estimates of the contamination of
the DVCS observables due to this associated pion
production processes when the experimental data are not fully exclusive, for a
set of kinematical conditions representative of present or planned experiments
at JLab, HERMES and COMPASS.Comment: 50 pages, 22 figure
The Counting of Generalized Polarizabilities
We demonstrate a concise method to enumerate the number of generalized
polarizabilities---quantities characterizing the independent observables in
singly-virtual Compton scattering---for a target particle of arbitrary spin s.
By using crossing symmetry and J^{PC} conservation, we show that this number is
(10s+1+delta_{s,0}).Comment: 10 pages, revtex4, no figures. Version to appear in Phys. Rev. D.
Paper now divided into sections and clarifying comments added, but physics
content unchange
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