42,374 research outputs found
Factorization is not violated
We show that existing proofs of factorization imply the cancellation of
certain multiladder contributions that Gotsman, Levin, and Maor had suggested
would invalidate the basic factorization theorem in QCD. No modifications of
the original argument are necessary, although the details of the example offer
useful insight into the mechanisms of factorization.Comment: 11 pages including 10 figure
Role of climate feedback on methane and ozone studied with a coupled ocean-atmosphere-chemistry model.
Fully Unintegrated Parton Correlation Functions and Factorization in Lowest Order Hard Scattering
Motivated by the need to correct the potentially large kinematic errors in
approximations used in the standard formulation of perturbative QCD, we
reformulate deeply inelastic lepton-proton scattering in terms of gauge
invariant, universal parton correlation functions which depend on all
components of parton four-momentum. Currently, different hard QCD processes are
described by very different perturbative formalisms, each relying on its own
set of kinematical approximations. In this paper we show how to set up
formalism that avoids approximations on final-state momenta, and thus has a
very general domain of applicability. The use of exact kinematics introduces a
number of significant conceptual shifts already at leading order, and tightly
constrains the formalism. We show how to define parton correlation functions
that generalize the concepts of parton density, fragmentation function, and
soft factor. After setting up a general subtraction formalism, we obtain a
factorization theorem. To avoid complications with Ward identities the full
derivation is restricted to abelian gauge theories; even so the resulting
structure is highly suggestive of a similar treatment for non-abelian gauge
theories.Comment: 44 pages, 69 figures typos fixed, clarifications and second appendix
adde
Quark fragmentation in the -vacuum
The vacuum of Quantum Chromodynamics is a superposition of degenerate states
with different topological numbers that are connected by tunneling (the
-vacuum). The tunneling events are due to topologically non-trivial
configurations of gauge fields (e.g. the instantons) that induce local \p-odd
domains in Minkowski space-time. We study the quark fragmentation in this
topologically non-trivial QCD background. We find that even though QCD globally
conserves \p and \cp symmetries, two new kinds of \p-odd fragmentation
functions emerge. They generate interesting dihadron correlations: one is the
azimuthal angle correlation usually referred to as
the Collins effect, and the other is the \p-odd correlation that vanishes in the cross section summed over many events, but
survives on the event-by-event basis. Using the chiral quark model we estimate
the magnitude of these new fragmentation functions. We study their experimental
manifestations in dihadron production in collisions, and comment on
the applicability of our approach in deep-inelastic scattering, proton-proton
and heavy ion collisions.Comment: 4 pages, 2 figure
A translator writing system for microcomputer high-level languages and assemblers
In order to implement high level languages whenever possible, a translator writing system of advanced design was developed. It is intended for routine production use by many programmers working on different projects. As well as a fairly conventional parser generator, it includes a system for the rapid generation of table driven code generators. The parser generator was developed from a prototype version. The translator writing system includes various tools for the management of the source text of a compiler under construction. In addition, it supplies various default source code sections so that its output is always compilable and executable. The system thereby encourages iterative enhancement as a development methodology by ensuring an executable program from the earliest stages of a compiler development project. The translator writing system includes PASCAL/48 compiler, three assemblers, and two compilers for a subset of HAL/S
Massive quark scattering at strong coupling from AdS/CFT
We extend the analysis of Alday and Maldacena for obtaining gluon scattering
amplitudes at strong coupling to include external massive quark states. Our
quarks are actually the N=2 hypermultiplets which arise when D7-brane probes
are included in the AdS_5 x S^5 geometry. We work in the quenched
approximation, treating the N=2 matter multiplets as external sources coupled
to the N=4 SYM fields. We first derive appropriate massive-particle boundary
conditions for the string scattering worldsheets. We then find an exact
worldsheet which corresponds to the scattering of two massive quarks and two
massless gluons and extract from this the associated scattering amplitude. We
also find the worldsheet and amplitude for the scattering of four massive
quarks. Our worldsheet solutions reduce to the four massless gluon solution of
Alday and Maldacena in the limit of zero quark mass. The amplitudes we compute
can also be interpreted in terms of 2-2 scattering involving gluons and massive
W-bosons.Comment: 46 pages, 11 figures, v4: additional comments added to intr
Transverse-Momentum Dependent Factorization for gamma^* pi^0 to gamma
With a consistent definition of transverse-momentum dependent (TMD)
light-cone wave function, we show that the amplitude for the process can be factorized when the virtuality of the initial photon is
large. In contrast to the collinear factorization in which the amplitude is
factorized as a convolution of the standard light-cone wave function and a hard
part, the TMD factorization yields a convolution of a TMD light-cone wave
function, a soft factor and a hard part. We explicitly show that the TMD
factorization holds at one loop level. It is expected that the factorization
holds beyond one-loop level because the cancelation of soft divergences is on a
diagram-by-diagram basis. We also show that the TMD factorization helps to
resum large logarithms of type .Comment: Published version in Phys.Rev.D75:014014,200
- …