159 research outputs found
Soft-collinear resummation in deeply virtual Compton scattering
We derive an all order resummation formula for the deeply virtual Compton
scattering (DVCS) amplitude, which takes into account soft gluon exchanges in
the non-singlet quark coefficient function. We identify the ladder diagrams
responsible in light-like gauge for [alphaS log^2 (x +/- xi)]^n contributions.
The resummed series results in a simple closed expression.Comment: 4 pages, 4 figure
Double logarithms resummation in exclusive processes : the surprising behavior of DVCS
Double logarithms resummation has been much studied in inclusive as well as
exclusive processes. The Sudakov mechanism has often be the crucial tool to
exponentiate potentially large contributions to amplitudes or cross-sections
near phase-space boundaries. We report on a recent work where a very different
pattern emerges : the DVCS quark coefficient function C(x,\xi) develops, near
the particular point x=\xi, a non-alternate series in \alpha_s^n
log^{2n}(x-\xi) which may be resummed in a cosh[K sqrt \alpha_s log(x-\xi)]
factor. This result is at odds with the known result for the corresponding
coefficient function for the pion transition form factor near the end point
C(z) although they are much related through a z -> x/\xi correspondence.Comment: 9 pages, 1 figure, Presented at the Low x workshop, May 30 - June 4
2013, Rehovot and Eilat, Israe
A consistent model for \pi N transition distribution amplitudes and backward pion electroproduction
The extension of the concept of generalized parton distributions leads to the
introduction of baryon to meson transition distribution amplitudes (TDAs),
non-diagonal matrix elements of the nonlocal three quark operator between a
nucleon and a meson state. We present a general framework for modelling nucleon
to pion () TDAs. Our main tool is the spectral representation for \pi N
TDAs in terms of quadruple distributions. We propose a factorized Ansatz for
quadruple distributions with input from the soft-pion theorem for \pi N TDAs.
The spectral representation is complemented with a D-term like contribution
from the nucleon exchange in the cross channel. We then study backward pion
electroproduction in the QCD collinear factorization approach in which the
non-perturbative part of the amplitude involves \pi N TDAs. Within our two
component model for \pi N TDAs we update previous leading-twist estimates of
the unpolarized cross section. Finally, we compute the transverse target single
spin asymmetry as a function of skewness. We find it to be sizable in the
valence region and sensitive to the phenomenological input of our \pi N TDA
model.Comment: 39 pages, 9 figure
Towards a solution of the charmonium production controversy: k_t-factorization versus color octet mechanism
The cross section of \chi_{cJ} hadroproduction is calculated in the
k_t-factorization approach. We find a significant contribution of the \chi_{c1}
state due to non-applicability of the Landau-Yang theorem because of off-shell
gluons. The results are in agreement with data and, in contrast to the
collinear factorization, show a dominance of the color singlet part and a
strong suppression of the color octet contribution. Our results could therefore
lead to a solution of the longstanding controversy between the color singlet
model and the color octet mechanism.Comment: 4 pages, 5 figures, final PRL versio
Effective Action for High-Energy Scattering in Gravity
The multi-Regge effective action is derived directly from the linearized
gravity action. After excluding the redundant field components we separate the
fields into momentum modes and integrate over modes which correspond neither to
the kinematics of scattering nor to the one of exchanged particles. The
effective vertices of scattering and of particle production are obtained as
sums of the contributions from the triple and quartic interaction terms and the
fields in the effective action are defined in terms of the two physical
components of the metric fluctuation.Comment: 15 pages, LATE
Solvability and PT-symmetry in a double-well model with point interactions
We show that and how point interactions offer one of the most suitable guides
towards a quantitative analysis of properties of certain specific non-Hermitian
(usually called PT-symmetric) quantum-mechanical systems. A double-well model
is chosen, an easy solvability of which clarifies the mechanisms of the
unavoided level crossing and of the spontaneous PT-symmetry breaking. The
latter phenomenon takes place at a certain natural boundary of the domain of
the "acceptable" parameters of the model. Within this domain the model mediates
a nice and compact explicit illustration of the not entirely standard
probabilistic interpretation of the physical bound states in the very recently
developed (so called PT symmetric or, in an alternative terminology,
pseudo-Hermitian) new, fairly exciting and very quickly developing branch of
Quantum Mechanics.Comment: 24 p., written for the special journal issue "Singular Interactions
in Quantum Mechanics: Solvable Models". Will be also presented to the int.
conference "Pseudo-Hermitian Hamiltonians in Quantum Physics III" (Instanbul,
Koc University, June 20 - 22, 2005)
http://home.ku.edu.tr/~amostafazadeh/workshop/workshop.ht
Relativistic treatment of harmonics from impurity systems in quantum wires
Within a one particle approximation of the Dirac equation we investigate a
defect system in a quantum wire. We demonstrate that by minimally coupling a
laser field of frequency omega to such an impurity system, one may generate
harmonics of multiples of the driving frequency. In a multiple defect system
one may employ the distance between the defects in order to tune the cut-off
frequency.Comment: 9 pages Latex, 8 eps figures, section added, numerics improve
Symmetry Properties of the Effective Action for High-Energy Scattering in QCD
We study the effective action describing high-energy scattering processes in
the multi-Regge limit of QCD, which should provide the starting point for a new
attempt to overcome the limitations of the leading logarithmic and the eikonal
approximations. The action can be obtained via simple graphical rules or by
integrating in the QCD functional integral over momentum modes of gluon and
quark fields that do not appear explicitely as scattering or exchanged
particles in the considered processes. The supersymmetry is used to obtain the
terms in the action involving quarks fields from the pure gluonic ones. We
observe a Weizs\"acker - Williams type relations between terms describing
scattering and production of particles.Comment: 37 pages LATEX, 1 Table and 7 figures using package FEYNMA
Direct J/Psi hadroproduction in k_\perp-factorization and the color octet mechanism
The hadroproduction of direct J/Psi in the framework of the
k_\perp-factorization approach is studied. The color-singlet contribution is
essentially larger than in the collinear approach but is still an order of
magnitude below the data. The deficit may be well described by the color octet
contribution with the value of the matrix element
substantially decreased in comparison with the fits in the collinear
factorization. This should lead to a reduction of the large transverse
polarization, predicted in the collinear approach.Comment: 3 pages, LaTeX, 2 eps figures, final PRD versio
A Large Hadron Electron Collider at CERN
This document provides a brief overview of the recently published report on
the design of the Large Hadron Electron Collider (LHeC), which comprises its
physics programme, accelerator physics, technology and main detector concepts.
The LHeC exploits and develops challenging, though principally existing,
accelerator and detector technologies. This summary is complemented by brief
illustrations of some of the highlights of the physics programme, which relies
on a vastly extended kinematic range, luminosity and unprecedented precision in
deep inelastic scattering. Illustrations are provided regarding high precision
QCD, new physics (Higgs, SUSY) and electron-ion physics. The LHeC is designed
to run synchronously with the LHC in the twenties and to achieve an integrated
luminosity of O(100) fb. It will become the cleanest high resolution
microscope of mankind and will substantially extend as well as complement the
investigation of the physics of the TeV energy scale, which has been enabled by
the LHC
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