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 $\rho$ 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 $f_{2}$ 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 $f_{2}$ mesons. We compute the differential cross-section in the $k_{\perp}$-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 $f_{2}$ mesons by comparing theoretical predictions of different parameterizations of the unintegrated gluon distribution function. We find that $f_{2}$-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 πe2\pi_{e2} Decay and Some Comments on μ−e\mu-e 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 $e^-e^\pm$ 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)