Calculation Of Radiative Corrections Research Articles

Radiative corrections to W +W − → W +W − in the electroweak standard model

The cross-section for W +W − → W +W − with arbitrarily polarized W bosons is calculated within the Electroweak Standard Model including the complete virtual and soft-photonic O (α) corrections. We show the numerical importance of the radiative corrections for the dominating polarized cross-sections and for the unpolarized cross-section. The numerical accuracy of the equivalence theorem is investigated in O (α) by comparing the cross-section for purely longitudinal W bosons obtained from the equivalence theorem and from the direct calculation. We point out that the instability of the W boson, which is inherent in the one-loop corrections, prevents a consistent calculation of radiative corrections to the scattering of on-real-mass-shell longitudinal W bosons beyond O (α).

Order-α radiative correction to 6He and 32Ar β decay recoil spectra

Order-α model independent radiative correction results to the 6He → 6Li and 32Ar → 32Cl β decay recoil spectra are presented. The effects of these corrections on the electron-neutrino correlation parameter ( a eν ) and the induced tensor form factor are discussed (taking into account the most important experimental details of these measurements). In the case of 6He beta decay, the shift of the a eν value due to our radiative correction calculation is larger than the total experimental error of the last, precise measurement. The order- Zα 2 radiative correction of the recoil spectrum is also estimated. Recoil-order formulae are given for the beta energy - recoil energy Dalitz distribution and the recoil spectrum.

Hard photon bremsstrahlung effects in hyperon semileptonic decays

An efficient Monte Carlo method for photon bremsstrahlung calculations in semileptonic decays is described. This method is useful for order-α radiative correction calculations, and for event generations in off-line Monte Carlo simulation programs. The order-α bremsstrahlung amplitude in hyperon semileptonic decays is given by using the Low-theorem, and the bremsstrahlung amplitude squared is calculated for unpolarized decays. Numerical calculation results are presented for n → pe v, μ → e v, v μ, Σ − → ne v and Λ → pe v decays. The general features of the Monte Carlo method might be useful for photon bremsstrahlung calculations in other decay and collision processes.

Order- α radiative correction calculations for oriented allowed nuclear β decays

A general method for the order- α radiative correction calculation in oriented nuclear β decays is presented. This methodis based upon the Monte Carlo event generation and integration procedure of F. Glück. The calculations are described in detail in the case of the zeroth order oriented β decays. The virtual, soft and hard photon bremsstrahlung formulae are then given. The method is useful for radiative correction calculations and for weighted or unweighted event generations in experimental off-line data analyses.

POLRAD 2.0. FORTRAN code for the radiative corrections calculation to deep inelastic scattering of polarized particles

The FORTRAN code POLRAD 2.0 for radiative correction calculation in inclusive and semi-inclusive deep inelastic scattering of polarized leptons by polarized nucleons and nuclei is described. Its theoretical basis, structure and algorithms are discussed in detail.

Order-α radiative correction calculations for unoriented allowed nuclear, neutron and pion β decays

An efficient Monte Carlo method for orderα photon bremsstrahlung calculations in allowed nuclear, neutron and pion beta decays is presented. This method is useful for radiative correction calculations and for weighted or unweighted event generations in experimental off-line data analyses. The most important intermediate steps of the calculations are also described. Several numerical results of the Monte Carlo program are compared with published analytical and numerical quadrature calculation results.

Monte Carlo type radiative correction calculations for neutron, muon and hyperon semileptonic decays

A new method of order-α electromagnetic radiative correction calculation is presented for neutron, muon and hyperon semileptonic decays. Using the formulae described in this paper one can compute radiative corrections to any possible quantities or distributions of these decays. This method is especially suitable for experimental analyses. It is also applicable for hard photon bremsstrahlung calculations of any high energy processes containing charged leptons among the final particles.

The proton asymmetry in neutron decay

Results of recoil-order, Coulomb and model-independent order-α radiative correction calculations for the proton asymmetry of neutron decay are presented. These corrections are important for the precise interpretations of the present and future proton asymmetry measurements. In addition to the case of the Standard Model, general model families are also discussed.

STATUS OF HIGHER-ORDER CORRECTIONS IN THE STANDARD ELECTROWEAK THEORY

We review recent theoretical progress in the computation of radiative corrections beyond one loop within the standard model of electroweak interactions, in both the gauge and Higgs sectors. In the gauge sector, we discuss universal corrections of [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], and those due to virtual [Formula: see text]-threshold effects, as well as specific corrections to [Formula: see text] of [Formula: see text], [Formula: see text] and [Formula: see text] including finite-mb effects. We also present an update of the hadronic contributions to Δα. Theoretical uncertainties, other than those due to the lack of knowledge of MH and mt, are estimated. In the Higgs sector, we report on the [Formula: see text] corrections to [Formula: see text] including those which are specific for the [Formula: see text] mode, the [Formula: see text] corrections to [Formula: see text] including the finite-mq terms, and the [Formula: see text] corrections to Γ(H → gg).

Present and future searches with e +e − colliders for the neutral Higgs bosons of the Minimal Supersymmetric Standard Model — the complete 1-loop analysis

New mass regions unexcluded by direct searches are revealed by an analysis of experimental results from LEP1 using full 1-loop diagrammatic calculations of radiative corrections in the MSSM. Simulations of experimental signal efficiencies and background rejection factors, and full 1-loop calculations are combined to study the sensitivity for neutral Higgs bosons at LEP2 and the NLC. Compared with previous studies based on an Effective Potential Approach, we identify mass regions where the discovery potential depends on the MSSM parameters other than the top and stop masses. We propose our method of interpretation to be adopted by the four LEP experiments for better precision. The possibility of the experimental distinction between the Higgs boson in the MSM and the lightest Higgs boson in the MSSM is discussed for the NLC.

Present and future searches with e+e− colliders for the neutral Higgs bosons of the Minimal Supersymmetric Standard Model - the complete 1-loop analysis

New mass regions unexcluded by direct searches are revealed by an analysis of experimental results from LEP1 using full 1-loop diagrammatic calculations of radiative corrections in the MSSM. Simulations of experimental signal efficiencies and background rejection factors, and full 1-loop calculations are combined to study the sensitivity for neutral Higgs bosons at LEP2 and the NLC. Compared with previous studies based on an Effective Potential Approach, we identify mass regions where the discovery potential depends on the MSSM parameters other than the top and stop masses. We propose our method of interpretation to be adopted by the four LEP experiments for better precision. The possibility of the experimental distinction between the Higgs boson in the MSM and the lightest Higgs boson in the MSSM is discussed for the NLC.

Quenching of spin operators in the calculation of radiative corrections for nuclear beta decay

Calculations of the axial-vector component to the radiative correction for superallowed Fermi 0 +→0 + nuclear beta decay are here modified with quenched rather than free-nucleon coupling constants for the axial-vector and electromagnetic interactions with nucleons. The result increases the deduced value of V ud but does not restore unitarity in the CKM matrix.

Dimensional reduction methods in QCD

We apply the technique of dimensional reduction to massless quantum chromodynamics. It is shown that compared to conventional dimensional regularization methods calculations of radiative corrections at the one-loop level are less involved. We discuss the use of helicity methods within this framework and as an application we evaluate the one-loop corrections to the parity-violating cross sections and to the quark forwardbackward asymmetric polarization in\(e^ + e^ - \to V \to q\bar q(g)\). Finally, we demonstrate that further simplifications occur in the computation of structure functions including the parity-violating structure function in quark- and gluoninitiated electroproduction processes.

Scalar two-loop integrals for gauge boson self-energy diagrams with a massless fermion loop

We present analytical formulae for a class of two-loop integrals needed for the calculation of higher order radiative corrections in the theory of electroweak interactions. They were derived independently with dispersion relations and Feynman parameters, where some nonstandard techniques were used.

Calculation and application of electroweak radiative corrections at HERA

The characteristic features of electroweak radiative corrections in deep-inelastic scattering at HERA are reviewed. Numerical results are presented and consequences for the applications of radiative corrections are discussed.

QED bremsstrahlung in semileptonic B and leptonic τ decays

In this paper we present semianalytical and Monte Carlo calculations of radiative corrections in semileptonic decays. For two decay channels, B±→D0e±v(γ) and τ→e±vv(γ), we compare numerical results on the electron spectrum from the exact analytical O(α) formula, the leading-log formula, and the approximate formula presently used in experimental analyses and Monte Carlo simulations. We estimate the physical precision of the presented results and propose a new prescription on how to treat QED bremsstrahlung effects in the B decays.

Measurable distributions of unpolarized neutron decay.

Several two- and one-dimensional distributions of unpolarized free-neutron decay are calculated. The results of the order-$\ensuremath{\alpha}$ model-independent radiative correction calculations are tabulated numerically. With these corrections the theoretical distributions become precise enough to make possible the determination of the ratio of the axial-vector to the vector weak coupling constants to a precision of \ensuremath{\sim}0.001.

Monte Carlo treatment of radiative corrections at HERA

I review some basic features of the Monte Carlo approach to the calculation of radiative corrections for neutral current deep inelastic scattering. Numerical results for the influence of phase space cuts on the size of radiative corrections are discussed.

A practicableγ 5-scheme in dimensional regularization

We present a new simpleγ5 regularization scheme. We discuss its use in the standard radiative correction calculations including the anomaly contributions. The new scheme features an anticommutingγ5 which leads to great simplifications in practical calculations. We carefully discuss the underlying mathematics of ourγ5-scheme which is formulated in terms of simple projection operations.

Numerical calculation of radiative corrections to the beta energy spectrum of semileptonic decays of light- and charm-quark charged baryons.

In this paper we calculate, for the \ensuremath{\beta} energy spectrum of several semileptonic decays of interest, the numerical values of the radiative correction coefficients of an analytic expression previously obtained. The results can be readily used in a Monte Carlo simulation in an experimental analysis of those decays. We estimate the theoretical uncertainty involved in the analytic expression and show that it remains small even in high-q decays. Therefore, that expression is valid for charm-baryon semileptonic decays, to a high degree of precision.