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Johannes Blümlein

Publications and source records attributed to Johannes Blümlein.

72 records · Page 4Linked to original sources
arXiv2004

Mellin Representation for the Heavy Flavor Contributions to Deep Inelastic Structure Functions

We derive semi--analytic expressions for the analytic continuation of the Mellin transforms of the heavy flavor QCD coefficient functions for neutral current deep inelastic scattering in leading and next-to-leading order to complex values of the Mellin variable $N$. These representations are used in Mellin--space QCD evolution programs to provide fast evaluations of the heavy flavor contributions to the structure functions $F_2(x,Q^2), F_L(x,Q^2)$ and $g_1(x,Q^2)$.

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arXiv2001

On the structure of the virtual Compton amplitude with additional final-state meson in the extended Bjorken region

Using the framework of the non-local light-cone expansion a systematic study is performed for the structure of the twist-2 contributions to the virtual Compton amplitude in polarized deep-inelastic non-forward scattering for general nucleon spin with an additional scalar meson in the final state. A useful kinematic parameterization allowing for appropriate triple-valued off-forward parton distribution amplitudes is given. One-variable amplitudes being adapted to the fixed parameters of the extended Bjorken region are introduced by decomposing the Compton amplitude into collinear and non-collinear components. These amplitudes obey Wandzura-Wilczek and Callan-Gross like relations. The evolution equations for all the distribution amplitudes are determined showing that the additional meson momentum does not appear in the evolution kernels. The generalization to $n$ outgoing mesons is given.

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arXiv2001

On the Anomalous Dimension of the Transversity Distribution $h_1(x,Q^2)$

We calculate the leading order anomalous dimension of the transversity structure function directly using three different methods, the local light-cone expansion in the forward case, the non-forward case, and the short-distance expansion of the forward Compton amplitude. Our results agree with the original calculation by Artru and Mekhfi [Z. Phys. {\bf 45} (1990) 669], which has been doubted recently. We also comment on the next-to-leading order anomalous dimension.

hep-ph↗
arXiv2000

Leptoquark Pair Production in γγScattering: Threshold Resummation

The possibilities to pair-produce leptoquarks in photon-photon collisions are discussed. QCD threshold corrections lead to a strong enhancement of the production cross section. Suitably long-lived leptoquarks ($Γ_Φ\lsim 100 \MeV$) may form Leptoquarkonium states.

hep-ph↗
arXiv2000

Quantum Fiel Theoretic Treatment of the Non-Forward Compton Amplitude in the Generalized Bjorken Region

A quantum field theoretic treatment of the leading light-cone part of the virtual Compton amplitude is presented. The twist-decomposition of the operators is performed by a group-theoretic procedure respecting the Lorentz group O(3,1). The twist-2 contributions to the Compton amplitude are calculated and it is shown that the electromagnetic current is conserved for these terms. Relations between the amplitude functions associated to the symmetric and asymmetric part of the Compton amplitude are derived. These relations generalize the Callan-Gross and Wandzura-Wilczek relations of forward scattering for the non-forward Compton amplitude.

hep-ph↗
arXiv2000

On the Structure of the Virtual Compton Amplitude in the Generalized Bjorken Region: Integral Relations

A systematic study is performed of the structure of the twist-2 contributions to the virtual Compton amplitude in deep-inelastic non-forward scattering for general spin states in the non-local light cone expansion. The gauge invariance is proven in this approach for the twist-2 contributions for non-forward scattering. Relations are derived between the contributing non-forward amplitudes.

hep-ph↗
arXiv2000

Analytic Continuation of Mellin Transforms up to two-loop Order

The analytic continuation of the Mellin transforms to complex values of N for the basic functions $g_i(x)$ of the momentum fraction x emerging in the quantities of massless QED and QCD up to two-loop order, as the unpolarized and polarized splitting functions, coefficient functions, and hard scattering cross sections for space- and time-like momentum transfer are evaluated. These Mellin transforms provide the analytic continuations of all finite harmonic sums up to the level of the threefold sums of transcendentality four, where the basis-set ${g_i(x)}$ consists of products of {\sc Nielsen}-integrals up to transcendentality four. The computer code {\tt ANCONT} is provided.

hep-ph↗
arXiv1999

Harmonic Sums and Mellin Transforms

The finite and infinite harmonic sums form the general basis for the Mellin transforms of all individual functions $f_i(x)$ describing inclusive quantities such as coefficient and splitting functions which emerge in massless field theories. We discuss the mathematical structure of these quantities.

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arXiv1996

QED and Electroweak Corrections to Deep Inelastic Scattering

We describe the state of the art in the field of radiative corrections for deep inelastic scattering. Different methods of calculation of radiative corrections are reviewed. Some new results for QED radiative corrections for polarized deep inelastic scattering at HERA are presented. A comparison of results obtained by the codes POLRAD and HECTOR is given for the kinematic regime of the HERMES experiment. Recent results on radiative corrections to deep inelastic scattering with tagged photons are briefly discussed.

hep-ph↗
arXiv1995

On the measurability of the structure function $g_1(X,Q^2)$ in $ep$ collisions at HERA

The possibility is investigated to measure the polarized structure function $g_1(x,Q^2)$ in the collider mode of HERA operating with a polarized lepton and proton beam. The $x$ dependence of $g_1$ can be measured at a statistical precision of $\sim 20\%~{\rm to}~80\%$ in the range $0.0005 < x < 0.5$ correlated to virtualities $15 < \langle Q^2 \rangle < 3500 \GeV^2$ at beam polarizations $λ_p \sim λ_e = 0.8$ and ${\cal L}_{int} = 60 \PB^{-1}$. At a low energy option, $E_p = 300 \GeV$, the statistical accuracy improves to values of $\sim 15\%~{\rm to}~50\%$ in the range $10^{-3} < x < 0.5$ and $10 < Q^2 < 800 \GeV^2$.

hep-ph↗
arXiv1995

On the Behaviour of Non--Singlet Structure Functions at Small $x$

The resummation of $O(α_s^{l+1} \ln^{2l} x)$ terms in the evolution kernels of non--singlet combinations of unpolarized and polarized structure functions is investigated. The agreement with complete calculations up to order $α_s^2$ is demonstrated, and the leading small-$x$ contributions to the three--loop non--singlet splitting functions $P^{\pm}$ are derived. The additional contributions due to the resummed terms are studied numerically for the most important non--singlet structure functions. They are found to be about $1\,\%$ or smaller in the kinematical regions accessible at present and in the foreseeable future.

hep-ph↗
arXiv1994

Small $x$ Contributions to the Structure Function $F_L(x,Q^2)$

The gluon contributions to $F_L(x,Q^2)$ in ${\cal O}(α_s)$ are calculated taking into account the transverse momentum of the initial state parton. In comparison with collinear factorization $F_L(x,Q^2)$, is not affected at large $x$ but takes smaller values in the small $x$ range. The onset of the $k_{\perp}$ effect is a function of $Q^2$.

hep-ph↗
arXiv1994

Leptoquark Pair Production at $ep$ Colliders

The pair production cross section for scalar and vector leptoquarks at $ep$ colliders is calculated for the case of photon--gluon fusion. In a model independent analysis we consider the most general $C$ and $P$ conserving couplings of gluons and photons to both scalar and vector leptoquarks described by an effective low--energy Lagangian which obeys $U(1)_{em} \times SU(3)_c$ invariance. Numerical predictions are given for the kinematical regime at HERA and LEP~$\otimes$~LHC.

hep-ph↗
arXiv1994

Do Deep Inelastic Scattering Data Favor a Light Gluino

A next--to--leading order QCD analysis of deep inelastic scattering data is performed allowing for contributions due to a light gluino. We obtain the values of $α_s(M_Z^2) \pm δα_s^{stat} = 0.108 \pm 0.002, 0.124 \pm 0.001, 0.145 \pm 0.009$ for QCD, SUSY QCD with a Majorana gluino and a Dirac gluino respectively. The value of $\alsm$ obtained in SUSY QCD with a Majorana gluino best agrees with the direct measurements of $α_s(M_Z^2)$ at LEP.

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