11,280 research outputs found
The annihilation of virtual photons into pseudoscalar mesons
We investigate the possibility to constrain the pion distribution amplitude
from the gamma* gamma* -> pi transition. For a surprisingly large range in the
two photon virtualities we find that the transition form factor is essentially
independent of the distribution amplitude. This in turn entails a
parameter-free prediction of QCD. The gamma* gamma* -> eta, eta' form factors
are also briefly discussed. We estimate that experimental studies might be
feasible at the existing e+ e- experiments BaBar, Belle, and CLEO.Comment: 22 pages latex, 9 figure
Two-Photon Annihilation into Baryon-Antibaryon Pairs
We study the handbag contribution to two-photon annihilation into
baryon-antibaryon pairs at large energy and momentum transfer. We derive
factorization of the process amplitude into a hard gamma gamma -> q qbar
subprocess and form factors describing the soft q qbar -> B Bbar transition,
assuming that the process is dominated by configurations where the (anti)quark
approximately carries the full momentum of the (anti)baryon. The form factors
represent moments of time-like generalized parton distributions, so-called B
Bbar distribution amplitudes. A characteristic feature of the handbag mechanism
is the absence of isospin-two components in the final state, which in
combination with flavor symmetry provides relations among the form factors for
the members of the lowest-lying baryon octet. Assuming dominance of the handbag
contribution, we can describe current experimental data with form factors of
plausible size, and predict the cross sections of presently unmeasured B Bbar
channels.Comment: 20 pages latex, 4 figures. v2: minor clarifications, references
update
Lattice-Boltzmann Model of Amphiphilic Systems
A lattice-Boltzmann model for the study of the dynamics of
oil-water-surfactant mixtures is constructed. The model, which is based on a
Ginzburg-Landau theory of amphiphilic systems with a single, scalar order
parameter, is then used to calculate the spectrum of undulation modes of an
oil-water interface and the spontaneous emulsification of oil and water after a
quench from two-phase coexistence into the lamellar phase. A comparison with
some analytical results shows that the model provides an accurate description
of the static and dynamic behavior of amphiphilic systems.Comment: 6 pages, 2 figures, europhysics-letter styl
The Overlap Representation of Skewed Quark and Gluon Distributions
Within the framework of light-cone quantisation we derive the complete and
exact overlap representation of skewed parton distributions for unpolarised and
polarised quarks and gluons. Symmetry properties and phenomenological
applications are discussed.Comment: LaTex, 36 pages. v2: incorrect paper attached originally. v3: erratum
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