6,177 research outputs found
Exclusive diffractive processes at HERA within the dipole picture
We present a simultaneous analysis, within an impact parameter dependent
saturated dipole model, of exclusive diffractive vector meson (J/psi, phi and
rho) production, deeply virtual Compton scattering and the total gamma* p cross
section data measured at HERA. Various cross sections measured as a function of
the kinematic variables Q^2, W and t are well described, with little
sensitivity to the details of the vector meson wave functions. We determine the
properties of the gluon density in the proton in both longitudinal and
transverse dimensions, including the impact parameter dependent saturation
scale. The overall success of the description indicates universality of the
emerging gluon distribution and proton shape.Comment: 48 pages, 28 figures, the final version to appear in Physical Review
Geometric Scaling in Inclusive Charm Production
We show that the cross section for inclusive charm production exhibits
geometric scaling in a large range of photon virtualities. In the HERA
kinematic domain the saturation momentum stays below the hard
scale , implying charm production probing mostly the color
transparency regime and unitarization effects being almost negligible. We
derive our results considering two saturation models which are able to describe
the DESY ep collider HERA data for the proton structure function at small
values of the Bjorken variable . A striking feature is the scaling on
above saturation limit, corroborating recent
theoretical studies.Comment: 4 pages, 2 figures. Version to be published in Physical Review
Letter
Effective action for the Regge processes in gravity
It is shown, that the effective action for the reggeized graviton
interactions can be formulated in terms of the reggeon fields and
and the metric tensor in such a way, that it is local in
the rapidity space and has the property of general covariance. The
corresponding effective currents and satisfy the
Hamilton-Jacobi equation for a massless particle moving in the gravitational
field. These currents are calculated explicitly for the shock wave-like fields
and a variation principle for them is formulated. As an application, we
reproduce the effective lagrangian for the multi-regge processes in gravity
together with the graviton Regge trajectory in the leading logarithmic
approximation with taking into account supersymmetric contributions.Comment: 39 page
Analytic properties of high energy production amplitudes in N=4 SUSY
We investigate analytic properties of the six point planar amplitude in N=4
SUSY at the multi-Regge kinematics for final state particles. For inelastic
processes the Steinmann relations play an important role because they give a
possibility to fix the phase structure of the Regge pole and Mandelstam cut
contributions. These contributions have the Moebius invariant form in the
transverse momentum subspace. The analyticity and factorization constraints
allow us to reproduce the two-loop correction to the 6-point BDS amplitude in
N=4 SUSY obtained earlier in the leading logarithmic approximation with the use
of the s-channel unitarity. The exponentiation hypothesis for the remainder
function in the multi-Regge kinematics is also investigated. The 6-point
amplitude in LLA can be completely reproduced from the BDS ansatz with the use
of the analyticity and Regge factorization.Comment: To appear in the proceedings of 16th International Seminar on High
Energy Physics, QUARKS-2010, Kolomna, Russia, 6-12 June, 2010. 15 page
The dipole representation of vector meson electroproduction beyond leading twist
We link the recent computation beyond leading twist of the impact factor of
the transition gamma*T -> rhoT performed in the light-cone collinear approach,
to the dipole picture by expressing the hard part of the process through its
Fourier transform in coordinate space. We show that in the Wandzura-Wilczek
approximation the impact factor up to twist 3 factorises in the wave function
of the photon combined with the distribution amplitudes of the rho-meson and
the colour dipole scattering amplitude with the t-channel gluons. We show also
that beyond the Wandzura-Wilczek approximation, the hard contribution of the
amplitude still exhibits the signature of the interaction of a single colour
dipole with the t-channel gluons. This result allows a phenomenological
approach of the helicity amplitudes of the leptoproduction of vector meson, by
combining our results to a dipole/target scattering amplitude model.Comment: 63 pages, 18 figure
Unifying approach to hard diffraction
We find a consistency between two different approaches of hard diffraction,
namely the QCD dipole model and the Soft Colour Interaction approach. A
theoretical interpretation in terms of S-Matrix and perturbative QCD properties
in the small regime is proposed.Comment: 4pages, 1 figure, letter submitted for publicatio
Non-forward NLO BFKL Kernel
Details of the calculation of the non-forward BFKL kernel at next-to-leading
order (NLO) are offered. Specifically we show the calculation of the two-gluon
production contribution. This contribution was the last missing part of the
kernel. Together with the NLO gluon Regge trajectory, the NLO contribution of
one-gluon production and the contribution of quark-antiquark production which
were found before it defines the kernel completely for any colour state in the
-channel, in particular the Pomeron kernel presented recently.Comment: 31 page
Odderon in baryon-baryon scattering from the AdS/CFT correspondence
Based on the AdS/CFT correspondence, we present a holographic description of
various C-odd exchanges in high energy baryon-baryon and baryon-antibaryon
scattering, and calculate their respective contributions to the difference in
the total cross sections. We predict that, due to the warp factor of AdS_5, the
total cross section in pp collisions is larger than in p\bar{p} collisions at
asymptotically high energies.Comment: 23 pages, v2: minor changes, to be published in JHE
Predispositions and the Political Behavior of American Economic Elites: Evidence from Technology Entrepreneurs
Economic elites regularly seek to exert political influence. But what policies do they support? Many accounts implicitly assume economic elites are homogeneous and that increases in their political power will increase inequality. We shed new light on heterogeneity in economic elites' political preferences, arguing that economic elites from an industry can share distinctive preferences due in part to sharing distinctive predispositions. Consequently, how increases in economic elites' influence affect inequality depends on which industry's elites are gaining influence and which policy issues are at stake. We demonstrate our argument with four original surveys, including the two largest political surveys of American economic elites to date: one of technology entrepreneurs—whose influence is burgeoning—and another of campaign donors. We show that technology entrepreneurs support liberal redistributive, social, and globalistic policies but conservative regulatory policies—a bundle of preferences rare among other economic elites. These differences appear to arise partly from their distinctive predispositions
The Meson Light-Cone Distribution Amplitudes of Leading Twist Revisited
We give a complete re-analysis of the leading twist quark-antiquark
light-cone distribution amplitudes of longitudinal and transverse
mesons. We derive Wandzura-Wilczek type relations between different
distributions and update the coefficients in their conformal expansion using
QCD sum rules including next-to-leading order radiative corrections. We find
that the distribution amplitudes of quarks inside longitudinally and
transversely polarized mesons have a similar shape, which is in
contradiction to previous analyses.Comment: 21 pages, latex2e, requires a4wide.sty and epsf.sty, 6 PS figures
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