366 research outputs found
The Gluonic Operator Matrix Elements at O(\alpha_s^2) for DIS Heavy Flavor Production
We calculate the gluonic operator matrix elements for the
twist--2 operators, which contribute to the heavy flavor Wilson coefficients in
unpolarized deeply inelastic scattering in the region , up to the
linear terms in the dimensional parameter , (). These quantities are required for the description of parton
distribution functions in the variable flavor number scheme (VFNS). The
terms contribute at the level of the
corrections through renormalization. We also comment on
additional terms, which have to be considered in the fixed (FFNV) and variable
flavor number scheme, adopting the scheme for the running
coupling constant.Comment: 12 pages Latex, 1 style fil
Production of massless charm jets in pp collisions at next-to-leading order of QCD
We present predictions for the inclusive production of charm jets in
proton-proton collisions at 7 TeV. Several CTEQ parton distribution functions
(PDFs) of the CTEQ6.6M type are employed, where two of the CTEQ6.6 PDFs have
intrinsic charm. At large enough jet transverse momentum and large jet
rapidity, the intrinsic charm content can be tested.Comment: 11 pages, 4 figure
Dynamical NNLO parton distributions
Utilizing recent DIS measurements (\sigma_r, F_{2,3,L}) and data on hadronic
dilepton production we determine at NNLO (3-loop) of QCD the dynamical parton
distributions of the nucleon generated radiatively from valencelike positive
input distributions at an optimally chosen low resolution scale (Q_0^2 < 1
GeV^2). These are compared with `standard' NNLO distributions generated from
positive input distributions at some fixed and higher resolution scale (Q_0^2 >
1 GeV^2). Although the NNLO corrections imply in both approaches an improved
value of \chi^2, typically \chi^2_{NNLO} \simeq 0.9 \chi^2_{NLO}, present DIS
data are still not sufficiently accurate to distinguish between NLO results and
the minute NNLO effects of a few percent, despite of the fact that the
dynamical NNLO uncertainties are somewhat smaller than the NLO ones and both
are, as expected, smaller than those of their `standard' counterparts. The
dynamical predictions for F_L(x,Q^2) become perturbatively stable already at
Q^2 = 2-3 GeV^2 where precision measurements could even delineate NNLO effects
in the very small-x region. This is in contrast to the common `standard'
approach but NNLO/NLO differences are here less distinguishable due to the much
larger 1\sigma uncertainty bands. Within the dynamical approach we obtain
\alpha_s(M_Z^2)=0.1124 \pm 0.0020, whereas the somewhat less constrained
`standard' fit gives \alpha_s(M_Z^2)=0.1158 \pm 0.0035.Comment: 44 pages, 15 figures; minor changes, footnote adde
First heavy flavor contributions to deeply inelastic scattering
In the asymptotic limit , the heavy flavor Wilson coefficients
for deep--inelastic scattering factorize into the massless Wilson coefficients
and the universal heavy flavor operator matrix elements resulting from
light--cone expansion. In this way, one can calculate all but the power
corrections in . The heavy flavor operator matrix elements
are known to . We present the last 2--loop result missing in the
unpolarized case for the renormalization at 3--loops and first 3--loop results
for terms proportional to the color factor in Mellin--space. In this
calculation, the corresponding parts of the anomalous dimensions
\cite{LARIN,MVVandim} are obtained as well.Comment: 6 pages, Contribution to the Proceedings of "Loops and Legs in
Quantum Field Theory", 2008, Sondershausen, Germany, and DIS 2008, London, U
What is the trouble with Dyson--Schwinger equations?
We discuss similarities and differences between Green Functions in Quantum
Field Theory and polylogarithms. Both can be obtained as solutions of fixpoint
equations which originate from an underlying Hopf algebra structure. Typically,
the equation is linear for the polylog, and non-linear for Green Functions. We
argue though that the crucial difference lies not in the non-linearity of the
latter, but in the appearance of non-trivial representation theory related to
transcendental extensions of the number field which governs the linear
solution. An example is studied to illuminate this point.Comment: 5 pages contributed to the proceedings "Loops and Legs 2004", April
2004, Zinnowitz, German
Identification of Cost Effective Energy Conservation Methods
In addition to a successful program of readily implemented conservation actions for reducing building energy consumption at Kennedy Space Center, recent detailed analyses have identified further substantial savings for buildings representative of technical facilities designed when energy costs were low. The techniques employed for determination of these energy savings consisted of facility configuration analysis, power and lighting measurements, detailed computer simulations and simulation verifications. Use of these methods resulted in identification of projected energy savings as large as $330,000 a year (approximately fwo year breakeven period) in a single building. Application of these techniques to other commercial buildings is discussed
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