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QCD-Instantons in eP Scattering
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DESY 97-114
hep-ph/9706400
QCD – Instantons in e±P Scattering1
S. Moch, A. Ringwald and F. Schrempp
DESY, Notkestr. 85, D-22603 Hamburg, Germany
Abstract. We review recent theoretical results from our systematic study of QCD-
instanton contributions to e±P processes, involving a hard momentum scale Q. The
main issues are: the absence of IR divergencies due to a dynamical suppression of
instantons with large size ρ 1/Q, the reliable calculability of instanton-induced
amplitudes and our inclusive framework to systematically calculate properties of the
I-induced multi-parton final state.
INTRODUCTION
Instantons [1] are well known to represent topology changing tunnelling transi-
tions in non-abelian gauge theories. These transitions induce processes which are
forbidden in perturbation theory, but have to exist in general [2] due to Adler-Bell-
Jackiw anomalies. Correspondingly, these processes imply a violation of certain
fermionic quantum numbers, notably, B + L in the electro-weak gauge theory and
chirality (Q5) in (massless) QCD.
An experimental discovery of such a novel, non-perturbative manifestation of
non-abelian gauge theories would clearly be of basic significance.
The interest in instanton (I)-induced processes during recent years has been
revived by the observation [3] that the strong exponential suppression, ∝
exp(?4π/α), of the corresponding tunnelling rates at low energies may be over-
come at high energies, mainly due to multi-gauge boson emission in addition to the
minimally required fermionic final state. Since αs ? αW , QCD-instantons are cer-
tainly much less suppressed than electro-weak ones. A pioneering and encouraging
theoretical estimate of the size of the QCD-instanton induced contribution to the
gluon structure functions in deep-inelastic scattering (DIS) was recently presented
in Ref. [4].
A systematic phenomenological and theoretical study is under way [5–11], which
clearly
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