1,359 research outputs found
QED Radiative Corrections to the Pionium Life Time
The lowest order QED radiative corrections to the cross-section of the
recharged process of transition of two charged pions to two neutral ones and to
the pionium life time are calculated in frames of scalar QED. It is argued that
the ultraviolet cut--off of the loop momentum is to be chosen of order of
meson mass. This fact permits to perform the calculation in frames of
Effective Chiral Lagrangian theory with vector-meson dominance. The Coulomb
factor corresponding to interaction in the initial state, shown, is to be
removed to avoid the double counting. Resulting value of the radiative
correction to the pionium life time is -0.25%.Comment: 4 pages, LaTeX (considerable improvements
QED radiative corrections to impact factors
We consider the radiative corrections to the impact factors of electron and
photon. According to a generalized eikonal representation the e\bar e
scattering amplitude at high energies and fixed momentum transfers is
proportional to the electron form factor. But we show that this representation
is violated due to the presence of non-planar diagrams. One loop correction to
the photon impact factor for small virtualities of the exchanged photon is
obtained using the known results for the cross section of the e\bar e
production at photon-nuclei interactions.Comment: 8 pp, plain LaTe
Tensor Meson Production in Proton-Proton Collisions from the Color Glass Condensate
We compute the inclusive cross-section of tensor mesons production in
proton-proton collisions at high-energy. We use an effective theory inspired
from the tensor meson dominance hypothesis that couples gluons to
mesons. We compute the differential cross-section in the
-factorization and in the Color Glass Condensate formalism in the
low density regime. We show that the two formalisms are equivalent for this
specific observable. Finally, we study the phenomenology of mesons by
comparing theoretical predictions of different parameterizations of the
unintegrated gluon distribution function. We find that -meson production
is another observable that can be used to put constraints on these
distributions.Comment: 26 pages, 3 figures, to be submitted in Phys. Rev.
Radiative Tail in Decay and Some Comments on Universality
The result of lowest-order perturbation theory calculations of the photon and
positron spectra in radiative pion(e2) decay are generalized to all orders of
perturbation theory using the structure-function method. An additional source
of radiative corrections to the ratio of the positron and muon channels of pion
decay, due to emission of virtual and real photons and pairs, is considered. It
depends on details of the detection of the final particles and is large enough
to be taken into account in theoretical estimates with a level of accuracy of
0.1%.Comment: 5 pages, LaTeX, some misprints are corrected, submitted to Pisma Zh.
Eksp. Teor. Fi
Helicity amplitudes for the small--angle process e^-e^{\pm}\to e^-\gamma\gamma + e^{\pm} with both photons along one direction and its cross channel
We study the small--angle double bremsstrahlung in scattering for
a jet kinematics where both photons move along the electron direction. This
region gives the main contribution to the cross section. We present analytic
expressions for all 64 amplitudes with arbitrary helicity states of the initial
and final leptons and the produced photons convenient for analytic and
numerical studies. The accuracy of the obtained amplitudes is given omitting
only terms of the order of m^2/E_j^2, \theta_j^2 and \theta_j m/E_j. The
helicity amplitudes for the cross channel \gamma e^\pm \to \gamma e^+e^- +
e^\pm are given. Several limits for the helicity amplitudes of hard or soft
final particles are considered.Comment: 20 pp, LaTeX, 7 EPS figs, uses elsart packag
The NLO N =4 SUSY BFKL Green function in the adjoint representation
We study the solution of the BFKL equation in the adjoint representation for
the N=4 SUSY theory at NLO accuracy. Consistency with the large momentum
transfer solution obtained by Fadin and Lipatov is found. We investigate, for
large and small values of the momentum transfer, the growth with energy of the
Green function, its collinear behaviour and the expansion in azimuthal angle
Fourier components.Comment: 7 pages, 4 figure
All Two-Loop MHV Amplitudes in Multi-Regge Kinematics From Applied Symbology
Recent progress on scattering amplitudes has benefited from the mathematical
technology of symbols for efficiently handling the types of polylogarithm
functions which frequently appear in multi-loop computations. The symbol for
all two-loop MHV amplitudes in planar SYM theory is known, but explicit
analytic formulas for the amplitudes are hard to come by except in special
limits where things simplify, such as multi-Regge kinematics. By applying
symbology we obtain a formula for the leading behavior of the imaginary part
(the Mandelstam cut contribution) of this amplitude in multi-Regge kinematics
for any number of gluons. Our result predicts a simple recursive structure
which agrees with a direct BFKL computation carried out in a parallel
publication.Comment: 20 pages, 2 figures. v2: minor correction
Tau and muon pair production cross-sections in electron-positron annihilations at sqrt{s} = 10.58 GeV
The calculational precision of \ee\to\tautau and \ee\to\mumu production
cross-sections in electron-positron annihilations at \roots = 10.58 \gev are
studied for the \kk Monte Carlo simulation program. We determine
\sigma(\ee\to\tautau) = (0.919 \pm 0.003) \nb and \sigma(\ee\to\mumu) =
(1.147 \pm 0.005) \nb, where the error represents the precision of the
calculation.Comment: 7 pages, 3 tables, 1 figure (published in Physical Review D 77,
054012 (2008)
- …