24,018 research outputs found
Electroproduction of vector mesons - factorization of end-point contributions
The end-point contributions in the quark longitudinal momentum fraction of
the virtual photon () to vector meson () impact factor to the
diffractive electroproduction amplitude can be factorized in terms of a
generalized parton evolution of the target parton distribution. The result is
used to model the helicity amplitudes in terms of small
generalized parton distributions.Comment: 24 pages LaTex, 4 eps-figure
Diffractive large transferred momentum photoproduction of vector mesons
The large behaviour of the helicity amplitudes of diffractive
photoproduction is estimated relying on models of the photon and meson
light-cone wave functions and on the double-logarithmic approximation to the
exchanged gluon interaction. The role of large-size colour dipole contributions
to the photon-meson transition impact factor is discussed.Comment: 13 pages LaTex, 3 figures, to appear in EPJ
(Vanishing) Twist in the Saddle-Centre and Period-Doubling Bifurcation
The lowest order resonant bifurcations of a periodic orbit of a Hamiltonian
system with two degrees of freedom have frequency ratio 1:1 (saddle-centre) and
1:2 (period-doubling). The twist, which is the derivative of the rotation
number with respect to the action, is studied near these bifurcations. When the
twist vanishes the nondegeneracy condition of the (isoenergetic) KAM theorem is
not satisfied, with interesting consequences for the dynamics. We show that
near the saddle-centre bifurcation the twist always vanishes. At this
bifurcation a ``twistless'' torus is created, when the resonance is passed. The
twistless torus replaces the colliding periodic orbits in phase space. We
explicitly derive the position of the twistless torus depending on the
resonance parameter, and show that the shape of this curve is universal. For
the period doubling bifurcation the situation is different. Here we show that
the twist does not vanish in a neighborhood of the bifurcation.Comment: 18 pages, 9 figure
On the polarization properties of the charmed baryon Lambda^+_c in the Lambda^+_c -> p + K^- + pi^+ + pi^0 decay
The polarization properties of the charmed Lambda^+_c baryon are investigated
in weak non-leptonic four-body Lambda^+_c -> p + K^- + pi^+ + pi^0 decay. The
probability of this decay and the angular distribution of the probability are
calculated in the effective quark model with chiral U(3)XU(3) symmetry
incorporating Heavy Quark Effective theory (HQET) and the extended
Nambu-Jona-Lasinio model with a linear realization of chiral U(3)XU(3)
symmetry. The theoretical value of the probability of the decay Lambda^+_c -> p
+ K^- + pi^+ + pi^0 relative to the probability of the decay Lambda^+_c -> p +
K^- + pi^+ does not contain free parameters and fits well experimental data.
The application of the obtained results to the analysis of the polarization of
the Lambda^+_c produced in the processes of photo and hadroproduction is
discussed.Comment: 10 pages, no figures, Late
Diffractive meson production from virtual photons with odd charge-parity exchange
We calculate the cross section of diffractive charge-parity C=+1 neutral
meson production in virtual photon proton collision at high energies. Due to
the opposite C-parities of photon and meson M (M = eta_C, pi^0, a_2) this
process probes the t-channel C=-1 odderon exchange which is described here as
noninteracting three-gluon exchange. Estimates for the cross section of the
inelastic diffractive process gamma^* p -> eta_C X_p are presented. The total
cross section of diffractive \eta_C meson photoproduction is found to be 47 pb.
The cross sections for the diffractive production of light mesons (pi^0, a_2)
in \gamma^* p collisions are of the same order if the photon virtuality Q^2 is
m^2_C.Comment: LaTeX, 19 pages, 8 ps-figs, epsfi
Boussinesq-type equations from nonlinear realizations of
We construct new coset realizations of infinite-dimensional linear
symmetry associated with Zamolodchikov's algebra which are
different from the previously explored Toda realization of
. We deduce the Boussinesq and modified Boussinesq equations as
constraints on the geometry of the corresponding coset manifolds.The main
characteristic features of these realizations are:i. Among the coset parameters
there are the space and time coordinates and which enter the Boussinesq
equations, all other coset parameters are regarded as fields depending on these
coordinates;ii. The spin 2 and 3 currents of and two spin 1 Kac-
Moody currents as well as two spin 0 fields related to the currents via
Miura maps, come out as the only essential parameters-fields of these cosets.
The remaining coset fields are covariantly expressed through them;iii.The Miura
maps get a new geometric interpretation as covariant constraints
which relate the above fields while passing from one coset manifold to another;
iv. The Boussinesq equation and two kinds of the modified Boussinesq equations
appear geometrically as the dynamical constraints accomplishing
covariant reductions of original coset manifolds to their two-dimensional
geodesic submanifolds;v. The zero-curvature representations for these equations
arise automatically as a consequence of the covariant reduction. The approach
proposed could provide a universal geometric description of the relationship
between -type algebras and integrable hierarchies.Comment: 23 pages, LaTe
N=2 Super - Algebra and N=2 Super Boussinesq Equations
We study classical super- algebra and its interplay with
supersymmetric extensions of the Boussinesq equation in the framework of the
nonlinear realization method and the inverse Higgs - covariant reduction
approach. These techniques have been previously applied by us in the bosonic
case to give a new geometric interpretation of the Boussinesq hierarchy.
Here we deduce the most general super Boussinesq equation and two kinds
of the modified super Boussinesq equations, as well as the super Miura
maps relating these systems to each other, by applying the covariant reduction
to certain coset manifolds of linear super- symmetry
associated with super-. We discuss the integrability properties of
the equations obtained and their correspondence with the formulation based on
the notion of the second hamiltonian structure.Comment: LaTeX, 30
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