2,082 research outputs found
F and D Values with Explicit Flavor Symmetry Breaking and \Delta s Contents of Nucleons
We propose a new model for describing baryon semi-leptonic decays for
estimating and values with explicit breaking effects of both SU(3) and
SU(2) flavor symmetry, where all possible SU(3) and SU(2) breaking effects are
induced from an effective interaction. An overall fit including the weak
magnetism form factor yields and with
d.o.f. with and . The spin content of strange quarks is estimated from the
obtained values and , and the nucleon spin problem is re-examined.
Furthermore, the unmeasured values of and for other hyperon
semi-leptonic decays are predicted from this new formula.Comment: 15 pages, 1 figure, final version to appear in PR
Theory Summary
A summary is presented of the more theoretical aspects of the presentations made at Hyperon~99. In addition, some material is covered which was not presented at the symposium but which I feel is pertinent to the main theme of hyperons and/or, more in particular, to discussions conducted during the symposium
Fit to the Bjorken, Ellis-Jaffe and Gross-Llewellyn-Smith sum rules in a renormalon based approach
We study the large order behaviour in perturbation theory of the Bjorken,
Ellis-Jaffe and Gross-Llewellyn-Smith sum rules. In particular, we consider
their first infrared renormalons, for which we obtain their analytic structure
with logarithmic accuracy and also an approximate determination of their
normalization constant. Estimates of higher order terms of the perturbative
series are given. The Renormalon subtracted scheme is worked out for these
observables and compared with experimental data. Overall, good agreement with
experiment is found. This allows us to obtain {\hat a}_0 and some higher-twist
non-perturbative constants from experiment: {\hat a}_0=0.141\pm 0.089;
f_{3,RS}(1 GeV)=-0.124^{+0.137}_{-0.142} GeV^2.Comment: 23 pages, 18 figures, one reference added, journal versio
Determination of the Kobayashi-Maskawa-Cabibbo matrix element V_{us} under various flavor-symmetry-breaking models in hyperon semileptonic decays
We study the success to describe hyperon semileptonic decays of four models
that incorporate second-order SU(3) symmetry breaking corrections. The criteria
to assess their success is by determining V_{us} in each of the three relevant
hyperon semileptonic decays and comparing the values obtained with one another
and also with the one that comes from K_{l3} decays. A strong dependence on the
particular symmetry breaking model is observed. Values of V_{us} which do not
agree with the one of K_{l3} are generally obtained. However, in the context of
chiral perturbation theory, only the model whose corrections are O(m_s) and
O(m_s^{3/2}) is successful. Using its predictions for the f_1 form factors one
can quote a value of V_{us} from this model, namely, V_{us}=0.2176\pm 0.0026,
which is in excellent agreement with the K_{l3} one.Comment: Final versio
Transversity K Factors for Drell-Yan
The question of the K factor in transversely polarised Drell-Yan (DY)
processes is examined. The transverse-spin case is peculiar for the absence of
a reference point in deeply inelastic scattering (DIS). Therefore, in order to
study more fully the possible effects of higher-order corrections on DY
asymmetries, a DIS definition for transversity is devised using a hypothetical
scalar (Higgs-like) vertex. The results show that some care may be required in
interpreting experimentally extracted partonic transversity, in particular when
comparing with model calculations or predictions.Comment: 8 pages, 4 figures (eps and feynmp); uses standard LaTeX/MiKTeX
packages [svjour.cls, amsmath, bbm, feynmp, graphicx, maybemath, natbib,
psfrag, slashed] some homespun packages (included in the zip file);
discussion augmented, 1 figure removed; resubmitted to Eur. Phys. J. section
Non-Universality and Evolution of the Sivers Function
We examine the large-x QCD evolution of the twist-three gluonic-pole strength
defining an effective T-odd Sivers function, where evolution of the T-even
transverse-spin DIS structure function g2 is multiplicative. The result
corresponds to a colour-factor modified spin-averaged twist-two evolution.Comment: Presented at the ECT* Workshop on Recent Advances in Perturbative QCD
and Hadronic Physics (20-25 July 2009} - final version (minor modifications
Gluon polarization in the proton
We combine heavy-quark renormalization group arguments with our understanding
of the nucleon's wavefunction to deduce a bound on the gluon polarization Delta
g in the proton. The bound is consistent with the values extracted from spin
experiments at COMPASS and RHIC.Comment: 4 page
A Matrix Approach to Numerical Solution of the DGLAP Evolution Equations
A matrix-based approach to numerical integration of the DGLAP evolution
equations is presented. The method arises naturally on discretisation of the
Bjorken x variable, a necessary procedure for numerical integration. Owing to
peculiar properties of the matrices involved, the resulting equations take on a
particularly simple form and may be solved in closed analytical form in the
variable t=ln(alpha_0/alpha). Such an approach affords parametrisation via data
x bins, rather than fixed functional forms. Thus, with the aid of the full
correlation matrix, appraisal of the behaviour in different x regions is
rendered more transparent and free of pollution from unphysical
cross-correlations inherent to functional parametrisations. Computationally,
the entire programme results in greater speed and stability; the matrix
representation developed is extremely compact. Moreover, since the parameter
dependence is linear, fitting is very stable and may be performed analytically
in a single pass over the data values.Comment: 13 pages, no figures, typeset with revtex4 and uses packages:
acromake, amssym
Towards an understanding of nucleon spin structure: from hard to soft scales
The workshop "The Helicity Structure of the Nucleon" (BNL June 5, 2006) was
organized as part of the 2006 RHIC & AGS Users' Meeting to review the status of
the spin problem and future directions. The presentations can be found at
http://www.phenix.bnl.gov/WWW/publish/caidala/UsersHelicityWorkshop2006/ .
Recent data suggests small polarized glue and strangeness in the proton. Here
we present a personal summary of the main results and presentations. What is
new and exciting in the data, and what might this tell us about the structure
of the proton ?Comment: 20 pages, to appear in Int. J. Mod. Phys.
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