209 research outputs found
Instanton-Induced Processes - An Overview
A first part of this review is devoted to a summary of our extensive studies
of the discovery potential for instanton(I)-induced, deep-inelastic processes
at HERA. Included are some key issues about I-perturbation theory, an
exploitation of crucial lattice constraints and a status report about the
recent I-search results by the HERA collaborations H1 and ZEUS in relation to
our predictions. Next follows a brief outline of an ongoing project concerning
a broad exploration of the discovery potential for hard instanton processes at
the LHC. I then turn to an overview of our work on high-energy processes,
involving larger-sized instantons. I shall mainly focus on the phenomenon of
saturation at small Bjorken-x from an instanton perspective. In such a
framework, the saturation scale is associated with the conspicuous average
instanton size (~0.5 fm), as known from lattice simulations. Another central
and intriguing result is the identification of the "Colour Glass Condensate"
with the QCD sphaleron state.Comment: 14 pages,14 figures, Invited plenary talk presented at the CERN -
DESY Workshop 2004/2005, "HERA and the LHC
Instanton-Induced Cross-Sections in Deep-Inelastic Scattering
We present our results for inclusive instanton-induced cross-sections in
deep-inelastic scattering, paying in particular attention to the residual
renormalization-scale dependencies. A ``fiducial'' kinematical region in the
relevant Bjorken variables is extracted from recent lattice simulations of QCD.
The integrated instanton-contribution to the cross-section at HERA
corresponding to this fiducial region is surprisingly large: It is in the
O(100) pb range, and thus remarkably close to the recently published
experimental upper bounds.Comment: 13 pages, 10 figure
Instanton-Driven Saturation at Small x
We report on the interesting possibility of instanton-driven gluon saturation
in lepton-nucleon scattering at small Bjorken-x. Our results crucially involve
non-perturbative information from high-quality lattice simulations. The
conspicuous, intrinsic instanton size scale ~ 0.5 fm, as known from the
lattice, turns out to determine the saturation scale. A central result is the
identification of the ``colour glass condensate'' with the QCD-sphaleron state.Comment: 14 pages, 9 figure
QCDINS 2.0 - A Monte Carlo generator for instanton-induced processes in deep-inelastic scattering
We describe a Monte Carlo event generator for the simulation of QCD-instanton
induced processes in deep-inelastic scattering (HERA). The QCDINS package is
designed as an ``add-on'' hard process generator interfaced to the general
hadronic event simulation package HERWIG. It incorporates the theoretically
predicted production rate for instanton-induced events as well as the essential
characteristics that have been derived theoretically for the partonic final
state of instanton-induced processes: notably, the flavour democratic and
isotropic production of the partonic final state, energy weight factors
different for gluons and quarks, and a high average multiplicity O(10) of
produced partons with a Poisson distribution of the gluon multiplicity. While
the subsequent perturbative evolution of the generated partons is always
handled by the HERWIG package, the final hadronization step may optionally be
performed also by means of the general hadronic event simulation package
JETSET.Comment: 51 pages, 3 figure
Towards the Phenomenology of QCD-Instanton Induced Particle Production
We present a first status report on a broad and systematic study of possible
manifestations of QCD-instantons at HERA. Considerable motivation comes from
the close analogy between instanton-induced violation in electroweak
processes and effects of QCD-instantons in deep inelastic scattering. We
concentrate on the high multiplicity final state structure, reminiscent of an
isotropically decaying ``fireball''. A set of experimental isolation criteria
is proposed. They serve to further enhance the striking event signature without
significantly suppressing the expected rates.Comment: 32 pages, latex, epsfig, 11 uuencoded figure
QCD-Instantons and Saturation at Small x
We briefly report on the contribution of QCD-instantons to the phenomenon of
saturation in deep-inelastic scattering (DIS) at small Bjorken-x. The
explicitly known instanton gauge field serves as a concrete realization of an
underlying non-perturbative saturation mechanism associated with strong
classical fields. Two independent strategies were pursued, with consistent
results: On the one hand, an approach starting from instanton-perturbation
theory was considered and on the other hand, the scattering of a Wilson loop in
an instanton gauge field background. In both cases, the conspicuous, intrinsic
instanton size scale ~ 0.5 fm, as known from the lattice, turns out to
determine the saturation scale.Comment: 6 pages, 2 figures, presented at the Workshop on Strong and
Electroweak Matter (SEWM 2002), October 2-5, 2002, Heidelberg, German
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