35 research outputs found
Positivity bounds on generalized parton distributions in impact parameter representation
New positivity bounds are derived for generalized (off-forward) parton
distributions using the impact parameter representation. These inequalities are
stable under the evolution to higher normalization points. The full set of
inequalities is infinite. Several particular cases are considered explicitly.Comment: 8 page
On the heavy quark mass expansion for the operator Qbar gamma_5 Q and the charm content of eta, eta'
Recently in the context of studies of the intrinsic charm content of the
nucleon and of the eta' meson two groups have arrived at different results for
the 1/m^3 term of the heavy quark expansion for operator
differing by the factor of six. We show that the form of both results violates
certain general conditions. Using the expression for the axial anomaly with the
finite Pauli-Villars regularization we obtain a new expression for 1/m^3 term
of the heavy quark expansion for . With this new result we
obtain an estimate for the constant f_{\eta'}^{(c)}=-2 MeV.Comment: 4 page
New inequality for Wilson loops from AdS/CFT
The strong subadditivity is the most important inequality which entanglement
entropy satisfies. Based on the AdS/CFT conjecture, entanglement entropy in CFT
is equal to the area of the minimal surface in AdS space. It is known that a
Wilson loop can also be holographically computed from the minimal surface in
AdS space. In this paper, we argue that Wilson loops also satisfy a similar
inequality, and find several evidences of it.Comment: 16 pages (removed unnecessary figures
Lorentz invariance relations among parton distributions revisited
We revisit the derivation of the so-called Lorentz invariance relations
between parton distributions. In the most important cases these relations
involve twist-3 and transverse momentum dependent parton distributions. It is
shown that these relations are violated if the path-ordered exponential is
taken into account in the quark correlator.Comment: 4 pages, minor changes, to appear in Phys. Lett.
Generalized parton distributions and double distributions for q q-bar pions
We consider two simple covariant models for pions (one with scalar and the
other with spin-1/2 constituents). Pion generalized parton distributions are
derived by integration over the light-cone energy. The model distributions are
consistent with all known properties of generalized parton distributions,
including positivity. We also construct the corresponding double distributions
by appealing to Lorentz invariance. These ostensibly constructed double
distributions lead to different generalized parton distributions that need not
respect the positivity constraints. This inconsistency arises from the
ambiguity inherent in defining double distributions in a one-component
formalism (even in the absence of the Polyakov-Weiss term). We demonstrate that
the correct model double distributions can be calculated from non-diagonal
matrix elements of twist-two operators.Comment: 10 pages, 7 figures, RevTex4, reference added, typos correcte
Transversity distributions in the nucleon in the large-N_c limit
We compute the quark and antiquark transversity distributions in the nucleon
at a low normalization point of 600 MeV in the large- limit, where the
nucleon can be described as a soliton of an effective chiral theory (chiral
quark-soliton model). The flavor-nonsinglet distributions, and , appear in leading order
of the -expansion, while the flavor-singlet distributions, and , are non-zero only in
next-to-leading order. The transversity quark and antiquark distributions are
found to be significantly different from the longitudinally polarized
distributions and , respectively, in contrast to the prediction of the naive
non-relativistic quark model. We show that this affects the predictions for the
spin asymmetries in Drell-Yan pair production in transversely polarized pp and
ppbar collisions.Comment: 45 pages, 16 figure
A detailed QCD analysis of twist-3 effects in DVCS observables
In this paper I present a detailed QCD analysis of twist-3 effects in the
Wandzura-Wilczek (WW) approximation in deeply virtual Compton scattering (DVCS)
observables for various kinematical settings, representing the HERA, HERMES,
CLAS and the planned EIC (electron-ion-collider) experiments. I find that the
twist-3 effects in the WW approximation are almost always negligible at
collider energies but can be large for low Q^2 and smaller x_bj in observables
for the lower energy, fixed target experiments directly sensitive to the real
part of DVCS amplitudes like the charge asymmetry (CA). Conclusions are then
drawn about the reliability of extracting twist-2 generalized parton
distributions (GPDs) from experimental data and a first, phenomenological,
parameterization of the LO and NLO twist-2 GPD , describing all the
currently available DVCS data within the experimental errors is given.Comment: 18 pages, 21 figures, uses Revtex4, final version to be published in
PRD, minor revisions due to referee suggestion
The Chiral Soliton Model for Arbitrary Colors and Flavors
The quantum numbers of the chiral soliton are derived for an arbitrary number
of colors and flavors
Isovector unpolarized quark distribution in the nucleon in the large-N_c limit
We calculate the isovector (flavor-nonsinglet) unpolarized quark- and
antiquark distributions in the nucleon at a low normalization point in the
large-N_c limit. The nucleon is described as a soliton of the effective chiral
theory. The isovector distribution appears in the next-to-leading order of the
1/N_c-expansion. Numerical results for the quark- and antiquark distributions
compare well with the parametrizations of the data at a low normalization
point. This large-N_c approach gives a flavor asymmetry of the antiquark
distribution (violation of the Gottfried sum rule) in good agreement with the
measurements.Comment: 31 pages, LaTeX, 1 table, 4 figures included using eps
On Size and Shape of the Average Meson Fields in the Semibosonized Nambu & Jona-Lasinio Model
We consider a two-flavor Nambu \& Jona-Lasinio model in Hartree approximation
involving scalar-isoscalar and pseudoscalar-isovector quark-quark interactions.
Average meson fields are defined by minimizing the effective Euklidean action.
The fermionic part of the action, which contains the full Dirac sea, is
regularized within Schwinger's proper-time scheme. The meson fields are
restricted to the chiral circle and to hedgehog configurations. The only
parameter of the model is the constituent quark mass which simultaneously
controls the regularization. We evaluate meson and quark fields
self-consistently in dependence on the constituent quark mass. It is shown that
the self-consistent fields do practically not depend on the constituent quark
mass. This allows us to define a properly parameterized reference field which
for physically relevant constituent masses can be used as a good approximation
to the exactly calculated one. The reference field is chosen to have correct
behaviour for small and large radii. To test the agreement between
self-consistent and reference fields we calculate several observables like
nucleon energy, mean square radius, axial-vector constant and delta-nucleon
mass splitting in dependence on the constituent quark mass. The agreement is
found to be very well. Figures available on request.Comment: 12 pages (LATEX), 3 figures available on request, report FZR 93-1