29 research outputs found
What can break the Wandzura--Wilczek relation?
We analyze the breaking of the Wandzura-Wilczek relation for the g_2
structure function, emphasizing its connection with transverse momentum
dependent parton distribution functions. We find that the relation is broken by
two distinct twist-3 terms, and clarify how these can be separated in
measurements of double-spin asymmetries in semi-inclusive deep inelastic
scattering. Through a quantitative analysis of available g_2 data we also show
that the breaking of the Wandzura-Wilczek relation can be as large as 15-30% of
the size of g_2.Comment: 12 page
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
Two particle correlations inside one jet at "Modified Leading Logarithmic Approximation" of Quantum Chromodynamics; I: exact solution of the evolution equations at small x
We discuss correlations between two particles in jets at high energy
colliders and exactly solve the MLLA evolution equations in the small x limit.
We thus extend the Fong-Webber analysis to the region away from the hump of the
single inclusive energy spectrum. We give our results for LEP, Tevatron and LHC
energies, and compare with existing experimental data.Comment: LaTeX, 49 pages, 57 .eps figures + one log
Topology in 2D CP**(N-1) models on the lattice: a critical comparison of different cooling techniques
Two-dimensional CP**(N-1) models are used to compare the behavior of
different cooling techniques on the lattice. Cooling is one of the most
frequently used tools to study on the lattice the topological properties of the
vacuum of a field theory. We show that different cooling methods behave in an
equivalent way. To see this we apply the cooling methods on classical
instantonic configurations and on configurations of the thermal equilibrium
ensemble. We also calculate the topological susceptibility by using the cooling
technique.Comment: 24 pages, 10 figures (from 16 eps files
Is the classical Bukhvostov-Lipatov model integrable? A Painlev\'e analysis
In this work we apply the Weiss, Tabor and Carnevale integrability criterion
(Painlev\'e analysis) to the classical version of the two dimensional
Bukhvostov-Lipatov model. We are led to the conclusion that the model is not
integrable classically, except at a trivial point where the theory can be
described in terms of two uncoupled sine-Gordon models
Nonforward anomalous dimensions of Wilson operators in N=4 super-Yang-Mills theory
We present the next-to-leading order results for universal non-forward
anomalous dimensions of Wilson twist-2 operators in N=4 supersymmetric
Yang-Mills theory. The whole calculation was performed using supersymmetric
Ward identities derived in this paper together with already known QCD results
and does not involve any additional calculation of diagrams. We also considered
one particular limit of our result, which could potentially be interesting in
the context of AdS/CFT correspondence.Comment: 15 pages, references added, typos corrected, version accepted in JHE
A lattice calculation of the nucleon's spin-dependent structure function g_2 revisited
Our previous calculation of the spin-dependent structure function g_2 is
revisited. The interest in this structure function is to a great extent
motivated by the fact that it receives contributions from twist-two as well as
from twist-three operators already in leading order of 1/Q^2 thus offering the
unique possibility of directly assessing higher-twist effects. In our former
calculation the lattice operators were renormalized perturbatively and mixing
with lower-dimensional operators was ignored. However, the twist-three operator
which gives rise to the matrix element d_2 mixes non-perturbatively with an
operator of lower dimension. Taking this effect into account leads to a
considerably smaller value of d_2, which is consistent with the experimental
data.Comment: 25 pages, 11 figure
Longitudinal quark polarization in transversely polarized nucleons.
Accounting for transverse momenta of the quarks, a longitudinal quark spin asymmetry exists in a transversely polarized nucleon target. The relevant leading quark distribution g_{1T}(x,k_T^2) can be measured in the semi-inclusive deep-inelastic scattering. The average k_T^2 weighted distribution function g^{(1)}_{1T} can be obtained directly from the inclusive measurement of g_2
Renormalization of gauge invariant composite operators in light-cone gauge
We generalize to composite operators concepts and techniques which have been
successful in proving renormalization of the effective Action in light-cone
gauge. Gauge invariant operators can be grouped into classes, closed under
renormalization, which is matrix-wise. In spite of the presence of non-local
counterterms, an ``effective" dimensional hierarchy still guarantees that any
class is endowed with a finite number of elements. The main result we find is
that gauge invariant operators under renormalization mix only among themselves,
thanks to the very simple structure of Lee-Ward identities in this gauge,
contrary to their behaviour in covariant gauges.Comment: 35100 Padova, Italy DFPD 93/TH/53, July 1993
documentstyle[preprint,aps]{revtex
Superconformal operators in N=4 super-Yang-Mills theory
We construct, in the framework of the N=4 SYM theory, a supermultiplet of
twist-two conformal operators and study their renormalization properties. The
components of the supermultiplet have the same anomalous dimension and enter as
building blocks into multi-particle quasipartonic operators. The latter are
determined by the condition that their twist equals the number of elementary
constituent fields from which they are built. A unique feature of the N=4 SYM
is that all quasipartonic operators with different SU(4) quantum numbers fall
into a single supermultiplet. Among them there is a subsector of the operators
of maximal helicity, which has been known to be integrable in the multi-color
limit in QCD, independent of the presence of supersymmetry. In the N=4 SYM
theory, this symmetry is extended to the whole supermultiplet of quasipartonic
operators and the one-loop dilatation operator coincides with a Hamiltonian of
integrable SL(2|4) Heisenberg spin chain.Comment: 45 pages, Latex, 4 figure