Higher order QCD corrections to the energy-energy correlation function

We calculate theO(α _s ² correction to the energy-energy correlation cross section using a Sterman-Weinberg type resolution criterion to account for higher-order/nonperturbative effects. We find that the energy-energy correlation function as well as the asymmetry is sensitive to the choice of resolution parameters.     

Higher order QCD corrections to an exclusive two-photon process

We calculate the next-to-leading order QCD corrections in the $\text{MS}$ scheme to the coefficient functions in an operator product expansion of the amplitude T(q², p²) for the process $\text{γ}{}^1\text{(q) + γ}{}^1\text{(p) →}\text{helicity-zero}$, flavour non-singlet meson in which ?q² is large and ?p² ? 0. For an asymptotic wave function the complete O(α_s) correction for a pseudoscalar meson is about 16% for p² = 0 and α_s = 0.3; most of this correction can be removed by using a modified evolution equation for the wave function, leaving a correction of about 7%. For large p² the complete O(α_s) correction for a pseudoscalar meson is about 10%. We discuss how our results can be combined with similar calculations for the pion form factor F_π(Q²) to give a prediction: F_π(Q²) = Aα_s(Q²)T_π²(q², 0)(1 + Bα_s) that is independent of the as yet unknown two-loop anomalous dimension matrix.     

Higher order corrections and the scale parameter in QCD

I estimate the influence of the higher order corrections on the determination of the scale parameter Λ². I find a sizeable effect (a reduction of Λ² by a factor 3 to 4). This factor can be relevant in the comparison of Λ² with the characteristic confinement parameters.     

Next-to-next-to-leading order corrections to three-jet observables in electron-positron annihilation

I report on a numerical program, which can be used to calculate any infrared safe three-jet observable in electron-positron annihilation to next-to-next-to-leading order in the strong coupling constant alpha(s). The results are compared to a recent calculation by another group. Numerical differences in three color factors are discussed and explained.     

Higher order QCD corrections to the photoproduction of a direct photon at HERA

The contribution of resolved photons to the photoproduction cross section of direct photons is reexamined. Higher order,O(α ² α _s), QCD corrections to this contribution are calculated and turn out to be important at HERA energies. The observation of direct photons in the medium-p _⊥ range (p _⊥～5 GeV/c) should provide the opportunity to measure the gluon content of the photon.     

Higher order QCD and quark mass corrections to the Z widths in the standard model

We estimate, in the scheme, the strenghts of the higher order QCD (_s², _s³) and quark mass (m_f², m_f⁴, _s(m_f², m_f⁴)) corrections to the Z widths in the standard model (SM). Then, we give improved SM predictions of these widths. The observables Γ_H/Γ_e and σ_H, which can be predicted and measured accurately are almost insensitive to the changes of the Higgs ( 40 GeV M_H 1 TeV) and top quark (M_zM_t230 GeV) masses. Then, they should be useful in the high precision tests of the SM> Improved estimates of some quantities related to the width which are sensitive to the top quark mass are also given.     

Next-to-leading order QCD corrections to spin-dependent hadron-pair photoproduction

We compute the next-to-leading order QCD corrections to the “direct” part of the spin-dependent cross section for hadron-pair photoproduction. The calculation is performed using largely analytical methods. We present a brief phenomenological study of our results, focusing on the K-factors and scale dependence of the next-to-leading order cross sections. This process is relevant for the extraction of the gluon polarization in present and future spin-dependent lepton–nucleon scattering experiments. PACS  13.88.+e; 12.38.Bx; 13.85.Ni     

Lowest order QED radiative corrections to five-fold differential cross section of hadron leptoproduction

The contribution of exclusive radiative tail to the cross section of semi-inclusive hadron leptoproduction has been calculated exactly for the first time. Although the experience of inclusive data analyses suggests us that the contribution of radiative tail from the elastic peak is of particular importance, similar effects in the semi-inclusive process were only recently estimated in the peaking approximation. The explicit expressions for the lepton part of the lowest order QED contribution of exclusive radiative tail to the five-fold differential cross section are obtained and discussed. Numerical estimates, provided within Jefferson Lab kinematic conditions, demonstrate rather large effects of the exclusive radiative tail in the region at semi-inclusive threshold and for high energy of detected hadron.     

Higher order QCD corrections to charged-lepton deep-inelastic scattering and global fits of parton distributions

We study the perturbative QCD corrections to the heavy-quark structure functions of charged-lepton deep-inelastic scattering and their impact on global fits of parton distributions. We include the logarithmically enhanced terms near threshold due to soft gluon resummation in the QCD corrections at next-to-next-to-leading order. We demonstrate that this approximation is sufficient to describe the available HERA data in most parts of the kinematic region. The threshold-enhanced next-to-next-to-leading order corrections improve the agreement between predictions based on global fits of the parton distribution functions and the HERA collider data even in the small-x region.     

Higher order corrections to the Grimus-Stockinger formula

For the Grimus-Stockinger formula the same dimensionless parameter of asymptotic expansion is found by several ways of calculations. This parameter strongly depends on the width of wave packet.     

Beyond leading order QCD perturbative corrections to the pion form factor

The order α_s²(Q²) corrections to the pion form factor, F_π(Q²), are calculated using perturbative quantum chromodynamics and dimensional regularization. In the $\text{MS}$ renormalization scheme these corrections are large. This means that reliable perturbative predictions cannot be made until momentum transfers, Q, of about 300–400 GeV are reached or unless one can sum the large perturbative terms to all orders. Attempts to reorganize the perturbation series so that the first term gives a better approximation of the complete sum indicate that at Q = 10 GeV the pion form factor may be about a factor of two larger than the leading order result.     

A note on the QCD corrections to forward-backward asymmetries of heavy-quark jets inZ decays

The measurement of the forward-backward asymmetries of heavy quarks provides one of the most precise determinations of sin² _W inZ decays. We discuss in detail the one-loop QCD radiative corrections to these asymmetries. Results are given for single heavy-quark jet asymmetries and asymmetries of the thrust axis, as well as for heavy-quark two-jet final states.     

Higher order corrections to asymptotic-de Sitter inflation

Since trans-Planckian considerations can be associated with the re-definition of the initial vacuum, we investigate further the influence of trans-Planckian physics on the spectra produced by the initial quasi-de Sitter(d S) state during inflation. We use the asymptotic-d S mode to study the trans-Planckian correction of the power spectrum to the quasi-d S inflation. The obtained spectra consist of higher order corrections associated with the type of geometry and harmonic terms sensitive to the fluctuations of space-time(or gravitational waves) during inflation.As an important result, the amplitude of the power spectrum is dependent on the choice of c, i.e. the type of spacetime in the period of inflation. Also, the results are always valid for any asymptotic d S space-time and particularly coincide with the conventional results for d S and flat space-time.     

QED corrections to DIS cross section with tagged photon

We calculate the QED corrections to the deep inelastic scattering cross section with tagged photon at HERA, taking into account the leading and next-to-leading contributions. Different types of event selection are investigated. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 367–372 (25 September 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.