848 research outputs found
Effective field theory approach to structure functions at small x
We relate the structure functions of deep inelastic lepton-nucleon scattering
to current-current correlation functions in a Euclidean field theory depending
on a parameter r. The r-dependent Hamiltonian of the theory is P0-(1-r)P3, with
P0 the usual Hamiltonian and P3 the third component of the momentum operator.
We show that small x in the structure functions correspond to the small r limit
of the effective theory. We argue that for r->0 there is a critical regime of
the theory where simple scaling relations should hold. We show that in this
framework Regge behaviour of the structure functions obtained with the hard
pomeron ansatz corresponds to a scaling behaviour of the matrix elements in the
effective theory where the intercept of the hard pomeron appears as a critical
index. Explicit expressions for various analytic continuations of structure
functions and matrix elements are given as well as path integral
representations for the matrix elements in the effective theory. Our aim is to
provide a framework for truely nonperturbative calculations of structure
functions at small x for arbitrary Q^2Comment: 41 pages, 5 figure
Pomeron Physics and QCD
We review some theoretical ideas concerning diffractive processes. We discuss
the Regge Ansatz for the pomeron and the two pomeron model. Then we present the
results obtained from nonperturbative QCD for high energy scattering. There we
can extract from elastic scattering data the parameters describing the QCD
vacuum, in particular the string tension.Comment: 15 pages, Contribution to the Ringberg Workshop on HERA Physics 200
Flavour Dynamics with General Scalar Fields
We consider a spontaneously broken gauge theory based on the standard model
(SM) group G = SU(2) x U(1) with scalar fields that carry arbitrary
representations of G, and we investigate some general properties of the charged
and neutral current involving these fields. In particular we derive the
conditions for having real or complex couplings of the Z boson to two different
neutral or charged scalar fields, and for the existence of CP-violating
Z-scalar-scalar couplings. Moreover, we study models with the same fermion
content as in the SM, with one SU(2) Higgs singlet, and an arbitrary number of
Higgs doublets. We show that the structure of the Z-Higgs boson and of the
Yukawa couplings in these models can be such that CP-violating Zb{\bar b}G form
factors which conserve chirality are induced at the one-loop level.Comment: 35 pages, LaTe
Optimal observables and phase-space ambiguities
Optimal observables are known to lead to minimal statistical errors on
parameters for a given normalised event distribution of a physics reaction.
Thereby all statistical correlations are taken into account. Therefore, on the
one hand they are a useful tool to extract values on a set of parameters from
measured data. On the other hand one can calculate the minimal constraints on
these parameters achievable by any data-analysis method for the specific
reaction. In case the final states can be reconstructed without ambiguities
optimal observables have a particularly simple form. We give explicit formulae
for the optimal observables for generic reactions in case of ambiguities in the
reconstruction of the final state and for general parameterisation of the
final-state phase space.Comment: 14 pages, 1 figure, minor changes in tex
Inclusive Quark Production in -Annihilation - A Path Integral Approach
The single-particle inclusive differential cross-section for a reaction
is written as imaginary part of a correlation function in a
forward scattering amplitude for in a modified effective theory.
In this modified theory the interaction Hamiltonian equals
of the original theory up to a certain time. Then there is a sign change and
becomes nonlocal. This is worked out in detail for scalar field
models and for QED plus the abelian gluon model. A suitable path integral for
direct calculations of inclusive cross sections is presented.Comment: Latex, 5 pages, 2 figures, talk given at the QCD 00 Euroconference,
Montpellier, 6-13 July 200
Large parity violating effects in atomic dysprosium with nearly degenerate Floquet eigenvalues
In this article we study effects of parity nonconservation in atomic
dysprosium, where one has a pair of nearly degenerate levels of opposite
parity. We consider the time evolution of this two-level system within
oscillatory electric and magnetic fields. These are chosen to have a periodical
structure with the same period, such that a Floquet matrix describes the time
evolution of the quantum states. We show that, if the states are unstable, the
eigenvalues of the Floquet matrix may have contributions proportional to the
square root of the parity violating interaction matrix element while they
are almost degenerate in their parity even part. This leads to beat frequencies
proportional to which are expected to be larger by several orders
of magnitude compared to ordinary P-violating contributions which are of order
. However, for the simple field configurations we considered, it still
seems to be difficult to observe these P-violating beat effects, since the
states decay too fast. On the other hand, we found that, within only a few
Floquet cycles, very large parity violating asymmetries with respect to
experimental setups of opposite chirality may be obtained. The electric and
magnetic fields as well as the time intervals necessary for this are in an
experimentally accessible range. For statistically significant effects beyond
one standard deviation a number of about atoms is required. Our ideas
may be applied directly to other 2-level atomic systems and different field
configurations. We hope that these ideas will stimulate experimental work in
this direction.Comment: Sep 1999, 29pp, 10 Fig
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