501 research outputs found
Baryon octet distribution amplitudes in Wandzura-Wilczek approximation
We study higher twist distribution amplitudes for the SU_F(3) baryon octet.
We identify independent functions for all baryons in the isospin symmetry limit
and calculate the Wandzura-Wilczek contributions to the twist-4 and 5
distributions amplitudes.Comment: 7 page
Strong and radiative decays of the Ds0*(2317) meson in the DK-molecule picture
We consider a possible interpretation of the new charm-strange meson
Ds0*(2317) as a hadronic molecule - a bound state of D and K mesons. Using an
effective Lagrangian approach we calculate the strong Ds0* to Ds pi0 and
radiative Ds0* to Ds* gamma decays. A new impact related to the DK molecular
structure of the Ds0*(2317) meson is that the presence of u(d) quarks in the D
and K mesons gives rise to a direct strong isospin-violating transition Ds0* to
Ds pi0 in addition to the decay mechanism induced by eta-pi0 mixing considered
previously. We show that the direct transition dominates over the eta-pi0
mixing transition in the Ds0* to Ds pi0 decay. Our results for the partial
decay widths are consistent with previous calculations.Comment: 22 pages, 4 figures, accepted for publication in Phys. Rev.
Ds0*(2317) and Ds1(2460) mesons in two-body B-meson decays
We analyze the branching ratios of B to D(*) + Ds0*(Ds1) decays using the
factorization hypothesis. The B to D(*) transition form factors are taken from
a model-independent analysis done by Caprini, Lellouch and Neubert based on
heavy quark spin symmetry and dispersive constraints, including short-distance
and power corrections. The leptonic decay constants fDs0* and fDs1 are
calculated assuming a molecular structure for the Ds0* and Ds1 mesons. The
calculated branching ratios of B-meson two-body decays are compared with
experimental data and other theoretical results.Comment: 12 pages, 2 figure
Model study of generalized parton distributions with helicity flip
Generalized parton distributions with helicity flip are studied in the quark
sector, within a simple version of the MIT bag model, assuming an SU(6) wave
function for the proton target. In the framework under scrutiny it turns out
that only the generalized transversity distribution, H_T^q, is non vanishing.
For this quantity, the forward limit is properly recovered and numerical
results are found to underestimate recent lattice data for its first moment.
Positivity bounds recently proposed are fulfilled by the obtained distribution.
The relevance of the analysis for the planning of measurements of the quark
generalized transversity is addressed.Comment: 15 pages, 4 figures; shortened version accepted for publication in
Phys. Rev.
Light Cone Sum Rules for gamma* N -> Delta Transition Form Factors
A theoretical framework is suggested for the calculation of gamma* N -> Delta
transition form factors using the light-cone sum rule approach. Leading-order
sum rules are derived and compared with the existing experimental data. We find
that the transition form factors in a several GeV region are dominated by the
``soft'' contributions that can be thought of as overlap integrals of the
valence components of the hadron wave functions. The ``minus'' components of
the quark fields contribute significantly to the result, which can be
reinterpreted as large contributions of the quark orbital angular momentumComment: 38 pages, 10 figures; some typos fixed and references added, to
appear in Phys. Rev.
Theory and phenomenology of helicity amplitudes for high energy exclusive leptoproduction of the rho-meson
We review here two approaches to describe hard leptoproduction of
transversally polarized rho-meson, based on recent calculation of the gamma*T
-> rhoT impact factor up to twist 3 accuracy in the collinear factorization
frame, including 2- and 3- particles Fock-states. The first approach uses a
model of the unintegrated gluon density (the proton impact factor) which allows
a comparison of our predictions with H1 and ZEUS data for the ratios of
helicity amplitudes T(gamma*T -> rhoT)/T(gamma*L -> rhoL) and T(gamma*T ->
rhoL)/T(gamma*L -> rhoL). In the second approach, we transform the gamma*T ->
rhoT impact factor into the impact parameter space. We show that the
transformed amplitude factorizes according to conventional dipole picture. We
shortly discuss a way to implement the nucleon saturation effects in our
approach.Comment: 5 pages, 2 figures, to appear in the proceedings of 6th International
Conference on Quarks and Nuclear Physics (QNP 2012), Palaiseau, France, April
16-20, 201
Methods For Evaluation Of The Education Quality In Higher Education Institutions
The article aims to disclose the essence of the “education quality” concept, to study the international approaches and concepts of the higher education quality evaluation, to analyze specific methods and tools within one of the approaches. Establishing education quality assessment necessitates choosing the teaching personnel of higher educational institution, as well as a target group of students and independent experts in the field of organization of the educational process, on a distance basis particularly. Monitoring requires using such methods as interviews, surveys, questionnaires, and similar. The results were processed according to the authors’ algorithm allowing to calculate the quality of education. The authors’ interpretation of the concept of “education quality” is proposed. Given the insufficient study of the topic of distance education in the domestic scientific discourse, authors’ attention to this problem is an important contribution to study of the issue of distance education. The methods used to evaluate the education quality in higher education institutions at the international level are an integral element in the development of the educational space, although they cause certain controversy and criticism. The authors advise to select the methods for evaluating the educational process quality with account of the specific evaluation stage and purpose
Tagging the pion quark structure in QCD
We combine the constraints on the pion quark structure available from
perturbative QCD, nonperturbative QCD (nonlocal QCD sum rules and light cone
sum rules) with the analysis of current data on F_{\pi\gamma\gamma^*}(Q^2),
including recent high-precision lattice calculations of the second moment of
the pion's distribution amplitude. We supplement these constraints with those
extracted from the renormalon approach by means of the twist-four contributions
to the pion distribution amplitude in order to further increase stability with
respect to related theoretical uncertainties. We show which regions in the
space of the first two non-trivial Gegenbauer coefficients a_2 and a_4 of all
these constraints overlap, tagging this way the pion structure to the highest
degree possible at present.Comment: V1: 6 pages, 2 figures, 1 table. V2: Two references added with
corresponding insertions in the text. Matches version published in PR
High Energy exclusive Leptoproduction of the rho-meson: Theory and Phenomenology
We describe the hard leptoproduction of transversally polarized rho-meson, up
to twist 3 accuracy, including 2- and 3- particles Fock-states, in the HERA
kinematics of high center-of-mass energy. We first build a model based on a
simple approach to the unintegrated gluon density (the parton impact factor)
that we compare with H1 and ZEUS data for the ratios of helicity amplitudes
T(gamma*T -> rhoT)/T(gamma*L -> rhoL) and T(gamma*T -> rhoL)/T(gamma*L -> rhoL)
and get a good description of the data. We also show how saturation effects can
be included in this model by extending the dipole representation of the
scattering amplitude in coordinate space up to twist 3.Comment: 4 pages, 3 figures, to appear in the proceedings of 20th
International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS
2012), Bonn, Germany, 26-30 March 201
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