Publications (28)5.83 Total impact
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Article: Scale dependence of twist-three contributions to single spin asymmetries
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ABSTRACT: We reexamine the scale dependence of twist-three correlation functions relevant for the single transverse spin asymmetry in the framework of collinear factorization. Evolution equations are derived for both the flavor-nonsinglet and flavor-singlet distributions and arbitrary parton momenta. Our results do not agree with the recent calculations of the evolution in the limit of vanishing gluon momentum. Possible sources for this discrepancy are identified. -
Article: QCD sum rules in the effective heavy quark theory
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ABSTRACT: We derive sum rules for the leptonic decay constant of a heavy-light meson in the effective heavy quark theory. We show that the summation of logarithms in the heavy quark mass by the renormalization group technique enhances considerably radiative corrections. Our result for the decay constant in the static limit agrees well with recent lattice calculations. Finite quark mass corrections are estimated. -
Article: Semileptonic form factors D →π, K and B →π, K from a fine lattice
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ABSTRACT: We extract the form factors relevant for semileptonic decays of D and B mesons from a relativistic computation on a fine lattice in the quenched approximation. The lattice spacing is a=0.04 fm (corresponding to a^{-1}=4.97 GeV), which allows us to run very close to the physical B meson mass, and to reduce the systematic errors associated with the extrapolation in terms of a heavy quark expansion. For decays of D and D_s mesons, our results for the physical form factors at q^2=0 are as follows: f_+^{D to pi}(0)= 0.74(6)(4), f_+^{D to K}(0)= 0.78(5)(4) and f_+^{D_s to K}(0)=0.68(4)(3). Similarly, for B and B_s we find: f_+^{B to pi}(0)=0.27(7)(5), f_+^{B to K}(0)=0.32(6)(6) and f_+^{B_s to K}(0)=0.23(5)(4). We compare our results with other quenched and unquenched lattice calculations, as well as with light-cone sum rule predictions, finding good agreement. -
Article: Threshold Pion Production at Large Momentum Transfers
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ABSTRACT: We consider threshold pion electroproduction on a proton target for photon virtualities in the region 1-10 GeV$^2$. The S-wave multipoles at threshold, $E_{0+}$ and $L_{0+}$, are calculated using light-cone sum rules. -
Article: Deep inelastic pion electroproduction at threshold
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ABSTRACT: We consider the cross section of the deep inelastic pion electroproduction on a proton target at threshold for Q2 in the region 5–10 GeV2. The corresponding amplitudes are described in terms of two form factors which we calculate using light-cone sum rules to leading order in QCD and including higher twist corrections. Our results suggest a considerable change from a small Q2 region that can be treated in the soft-pion limit using current algebra. In particular, we obtain a π0 to π+ production ratio of order 1/3 and significant nucleon helicity-flip contributions. -
Article: Semileptonic inclusive B decays and the determination of |Vub| from QCD sum rules
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ABSTRACT: We calculate the electron spectrum of semileptonic decays of B mesons into noncharmed hadrons. The shape of the spectrum obtained from QCD sum rules is in general agreement with quark model calculations. At high electron energies the decrease of the spectrum is less steep than predicted by Altarelli et al. Our analysis yields a total decay rate Γ(B→Xueν̅ )=(6.8±2.0)×1013|Vub|2 s-1. For the spectrum integrated over electron energies in the interval 2.4 GeV≤Ee≤2.6 GeV in the laboratory frame we obtain Γ(B→Xueν̅ )=(5.0±1.6)×1012|Vub|2 s-1. Estimating all sorts of theoretical uncertainties, we obtain |Vub|=0.003±0.001 for the b→u weak transition matrix element from the new CLEO data. -
Article: Ioffe-time distributions instead of parton momentum distributions in the description of deep inelastic scattering
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ABSTRACT: We argue that parton distributions in coordinate space provide a more natural object for nonperturbative methods compared to the usual momentum distributions in which the physics of different longitudinal distances is being mixed. To illustrate the advantages of the coordinate space formulation, we calculate the coordinate space distributions for valence quarks in the proton using the QCD sum rule approach. A remarkable agreement is found between the calculated and the experimentally measured u-quark distribution up to light-cone distances Δ-=Δ0-Δ3 of order ∼1 fm in the proton rest frame. The calculation for valence d quarks gives much worse results; the reasons for this discrepancy are discussed. -
Article: Decays of mesons with charm quarks on the lattice
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ABSTRACT: We investigate mesons containing charm quarks on fine lattices with a^{-1} \sim 5 GeV. The quenched approximation is employed using the Wilson gauge action at \beta = 6.6 and nonperturbatively O(a) improved Wilson quarks. We present results for decay constants using various interpolating fields and give preliminary results for form factors of semileptonic decays of D_s mesons to light pseudoscalar mesons.
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Institutions
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2007–2009
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Universität Regensburg
- Institut für Theoretische Physik
Regensburg, Bavaria, Germany
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