20,798 research outputs found
Parton Distributions in the Virtual Photon Target and Factorization Scheme Dependence
We investigate parton distributions in the virtual photon target, both
polarized and unpolarized, up to the next-leading order (NLO) in QCD. Parton
distributions can be predicted completely up to NLO, but they are
factorization-scheme-dependent. We analyze parton distributions in several
factorization schemes and discuss their scheme dependence. Particular
attentions are paid to the axial anomaly effect on the first moments of the
polarized quark parton distributions, and also to the large- behaviors of
polarized and unpolarized parton distributions.Comment: 6 pages, LaTeX, 3 ps figures, uses npb.sty, Contribution to the
Zeuthen Workshop on Elementary Particle Theory: Loops and Legs in Quantum
Field Theory, Koenigstein-Weissig, Germany, April 200
Three-dimensional analysis of the surface mode supported in \v{C}erenkov and Smith-Purcell free-electron lasers
In \v{C}erenkov and Smith-Purcell free-electron lasers (FELs), a resonant
interaction between the electron beam and the co-propagating surface mode can
produce copious amount of coherent terahertz (THz) radiation. We perform a
three-dimensional (3D) analysis of the surface mode, taking the effect of
attenuation into account, and set up 3D Maxwell-Lorentz equations for both
these systems. Based on this analysis, we determine the requirements on the
electron beam parameters, i.e., beam emittance, beam size and beam current for
the successful operation of a \v{C}erenkov FEL
Polarized Parton Distributions in the Photon and Factorization Scheme Dependence
Spin-dependent parton distributions in the polarized virtual photon are
investigated in QCD up to the next-to-leading order (NLO). In the case
, where () is the mass squared of the
probe (target) photon, parton distributions can be predicted completely up to
the NLO, but they are factorization-scheme-dependent. Parton distributions are
analyzed in four different factorization schemes and their scheme dependence
are discussed. Particular attentions are paid to the axial anomaly effect on
the first moments of quark parton distributions, and also to the large-
behaviors of the parton distributions. Gluon distribution in the virtual photon
is found to be factorization-scheme independent up to the NLO.Comment: 15 pages, LaTeX, 3 postscript figures; one page shortened, refined
arguments, no change in results and conclusion
Factorization and NNLL Resummation for Higgs Production with a Jet Veto
Using methods of effective field theory, we derive the first all-order
factorization theorem for the Higgs-boson production cross section with a jet
veto, imposed by means of a standard sequential recombination jet algorithm.
Like in the case of small-q_T resummation in Drell-Yan and Higgs production,
the factorization is affected by a collinear anomaly. Our analysis provides the
basis for a systematic resummation of large logarithms log(m_H/p_T^veto) beyond
leading-logarithmic order. Specifically, we present predictions for the
resummed jet-veto cross section and efficiency at next-to-next-to-leading
logarithmic order. Our results have important implications for Higgs-boson
searches at the LHC, where a jet veto is required to suppress background
events.Comment: 28 pages, 5 figures; v2: published version; note added in proo
Parton distributions in the virtual photon target up to NNLO in QCD
Parton distributions in the virtual photon target are investigated in
perturbative QCD up to the next-to-next-to-leading order (NNLO). In the case
, where () is the mass squared of the
probe (target) photon, parton distributions can be predicted completely up to
the NNLO, but they are factorisation-scheme-dependent. We analyse parton
distributions in two different factorisation schemes, namely and
schemes, and discuss their scheme dependence. We show that
the factorisation-scheme dependence is characterised by the large-
behaviours of quark distributions. Gluon distribution is predicted to be very
small in absolute value except in the small- region.Comment: 28 pages, 5 figures, version to appear in Eur. Phys. J.
Multidimensional sampling for simulation and integration: measures, discrepancies, and quasi-random numbers
This is basically a review of the field of Quasi-Monte Carlo intended for
computational physicists and other potential users of quasi-random numbers. As
such, much of the material is not new, but is presented here in a style
hopefully more accessible to physicists than the specialized mathematical
literature. There are also some new results: On the practical side we give
important empirical properties of large quasi-random point sets, especially the
exact quadratic discrepancies; on the theoretical side, there is the exact
distribution of quadratic discrepancy for random point sets.Comment: 51 pages. Full paper, including all figures also available at:
ftp://ftp.nikhef.nl/pub/preprints/96-017.ps.gz Accepted for publication in
Comp.Phys.Comm. Fixed some typos, corrected formula 108,figure 11 and table
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