4,140 research outputs found
Reductions of integrable equations on A.III-type symmetric spaces
We study a class of integrable non-linear differential equations related to
the A.III-type symmetric spaces. These spaces are realized as factor groups of
the form SU(N)/S(U(N-k) x U(k)). We use the Cartan involution corresponding to
this symmetric space as an element of the reduction group and restrict generic
Lax operators to this symmetric space. The symmetries of the Lax operator are
inherited by the fundamental analytic solutions and give a characterization of
the corresponding Riemann-Hilbert data.Comment: 14 pages, 1 figure, LaTeX iopart styl
On a realization of -expansion in QCD
We suggest a simple algebraic approach to fix the elements of the -expansion for renormalization group invariant quantities, which uses
additional degrees of freedom. The approach is discussed in detail for NLO
calculations in QCD with the MSSM gluino -- an additional degree of freedom. We
derive the formulae of the -expansion for the nonsinglet Adler
-function and Bjorken polarized sum rules in the actual NLO within this
quantum field theory scheme with the MSSM gluino and the scheme with the second
additional degree of freedom. We discuss the properties of the -expansion for higher orders considering the NLO as an example.Comment: 14 pages, Introduction, Sec.2, Conclusion are significantly improve
Endpoint behavior of the pion distribution amplitude in QCD sum rules with nonlocal condensates
Starting from the QCD sum rules with nonlocal condensates for the pion
distribution amplitude, we derive another sum rule for its derivative and its
"integral" derivatives---defined in this work. We use this new sum rule to
analyze the fine details of the pion distribution amplitude in the endpoint
region . The results for endpoint-suppressed and flat-top (or
flat-like) pion distribution amplitudes are compared with those we obtained
with differential sum rules by employing two different models for the
distribution of vacuum-quark virtualities. We determine the range of values of
the derivatives of the pion distribution amplitude and show that
endpoint-suppressed distribution amplitudes lie within this range, while those
with endpoint enhancement---flat-type or CZ-like---yield values outside this
range.Comment: 20 pages, 10 figures, 1 table, conclusions update
Cut moments and a generalization of DGLAP equations
We elaborate a cut (truncated) Mellin moments (CMM) approach that is
constructed to study deep inelastic scattering in lepton-hadron collisions at
the natural kinematic constraints. We show that generalized CMM obtained by
multiple integrations of the original parton distribution as well
as ones obtained by multiple differentiations of this also satisfy
the DGLAP equations with the correspondingly transformed evolution kernel
. Appropriate classes of CMM for the available experimental kinematic
range are suggested and analyzed. Similar relations can be obtained for the
structure functions , being the Mellin convolution , where
is the coefficient function of the process.Comment: 11 page
New extended Crewther-type relation
We propose a conjecture about the detailed structure of the conformal
symmetry breaking term in the generalized Crewther relation. We conclude that
this conjecture leads to new relations between the QCD expansion coefficients
of the Adler D-function and the polarized Bjorken sum rule BComment: Second part of the talk presented at RADCOR2009-9th International
Symposium on Radiative Corrections (Applications of Quantum Field Theory to
Phenomenology), October 25-30, Ascona, Switzerland, Submitted to the
Proceeding
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