547 research outputs found
N=4 superconformal Ward identities for correlation functions
In this paper we study the four-point correlation function of the
energy-momentum supermultiplet in theories with N=4 superconformal symmetry in
four dimensions. We present a compact form of all component correlators as an
invariant of a particular abelian subalgebra of the N=4 superconformal algebra.
This invariant is unique up to a single function of the conformal cross-ratios
which is fixed by comparison with the correlation function of the lowest
half-BPS scalar operators. Our analysis is independent of the dynamics of a
specific theory, in particular it is valid in N=4 super Yang-Mills theory for
any value of the coupling constant. We discuss in great detail a subclass of
component correlators, which is a crucial ingredient for the recent study of
charge-flow correlations in conformal field theories. We compute the latter
explicitly and elucidate the origin of the interesting relations among
different types of flow correlations previously observed in arXiv:1309.1424.Comment: 41 page
Superconformal constraints for QCD conformal anomalies
Anomalous superconformal Ward identities and commutator algebra in N = 1
super-Yang-Mills theory give rise to constraints between the QCD special
conformal anomalies of conformal composite operators. We evaluate the
superconformal anomalies that appear in the product of renormalized conformal
operators and the trace anomaly in the supersymmetric spinor current and check
the constraints at one-loop order. In this way we prove the universality of QCD
conformal anomalies, which define the non-diagonal part of the anomalous
dimension matrix responsible for scaling violations of exclusive QCD amplitudes
at the next-to-leading order.Comment: 30 pages, 2 figures, LaTe
Event shapes in N=4 super-Yang-Mills theory
We study event shapes in N=4 SYM describing the angular distribution of
energy and R-charge in the final states created by the simplest half-BPS scalar
operator. Applying the approach developed in the companion paper
arXiv:1309.0769, we compute these observables using the correlation functions
of certain components of the N=4 stress-tensor supermultiplet: the half-BPS
operator itself, the R-symmetry current and the stress tensor. We present
master formulas for the all-order event shapes as convolutions of the Mellin
amplitude defining the correlation function of the half-BPS operators, with a
coupling-independent kernel determined by the choice of the observable. We find
remarkably simple relations between various event shapes following from N=4
superconformal symmetry. We perform thorough checks at leading order in the
weak coupling expansion and show perfect agreement with the conventional
calculations based on amplitude techniques. We extend our results to strong
coupling using the correlation function of half-BPS operators obtained from the
AdS/CFT correspondence.Comment: 52 pages, 6 figures; v2: typos correcte
Energy-energy correlations in N=4 SYM
We present a new approach to computing energy-energy correlations in gauge
theories that exploits their relation to correlation functions and bypasses the
use of scattering amplitudes. We illustrate its power by calculating
energy-energy correlations in the maximally supersymmetric Yang-Mills theory
(N=4 SYM) in the next-to-leading order approximation.Comment: 5 page
From correlation functions to event shapes
We present a new approach to computing event shape distributions or, more
precisely, charge flow correlations in a generic conformal field theory (CFT).
These infrared finite observables are familiar from collider physics studies
and describe the angular distribution of global charges in outgoing radiation
created from the vacuum by some source. The charge flow correlations can be
expressed in terms of Wightman correlation functions in a certain limit. We
explain how to compute these quantities starting from their Euclidean analogues
by means of a non-trivial analytic continuation which, in the framework of CFT,
can elegantly be performed in Mellin space. The relation between the charge
flow correlations and Euclidean correlation functions can be reformulated
directly in configuration space, bypassing the Mellin representation, as a
certain Lorentzian double discontinuity of the correlation function integrated
along the cuts. We illustrate the general formalism in N=4 SYM, making use of
the well-known results on the four-point correlation function of half-BPS
scalar operators. We compute the double scalar flow correlation in N=4 SYM, at
weak and strong coupling and show that it agrees with known results obtained by
different techniques. One of the remarkable features of the N=4 theory is that
the scalar and energy flow correlations are proportional to each other.
Imposing natural physical conditions on the energy flow correlations
(finiteness, positivity and regularity), we formulate additional constraints on
the four-point correlation functions in N=4 SYM that should be valid at any
coupling and away from the planar limit.Comment: 40 pages, 1 figure; v2: typos correcte
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
Integrability in Yang-Mills theory on the light cone beyond leading order
The one-loop dilatation operator in Yang-Mills theory possesses a hidden
integrability symmetry in the sector of maximal helicity Wilson operators. We
calculate two-loop corrections to the dilatation operator and demonstrate that
while integrability is broken for matter in the fundamental representation of
the SU(3) gauge group, for the adjoint SU(N_c) matter it survives the conformal
symmetry breaking and persists in supersymmetric N=1, N=2 and N=4 Yang-Mills
theories.Comment: 4 pages, 2 figure
Invariant Measures and Convergence for Cellular Automaton 184 and Related Processes
For a class of one-dimensional cellular automata, we review and complete the
characterization of the invariant measures (in particular, all invariant phase
separation measures), the rate of convergence to equilibrium, and the
derivation of the hydrodynamic limit. The most widely known representatives of
this class of automata are: Automaton 184 from the classification of S.
Wolfram, an annihilating particle system and a surface growth model.Comment: 18 page
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