1,610 research outputs found
Electrons and Photons: Fact not Fiction
The particle Fock space of the matter fields in QED can be constructed using
the free creation and annihilation operators. However, these particle operators
are not, even at asymptotically large times, the modes of the matter fields
that enter the QED Lagrangian. In this letter we construct the fields which do
recover such particle modes at large times. We are thus able to demonstrate for
the first time that, contrary to statements found in the literature, a
relativistic description of charged particles in QED exists.Comment: 8 pages, LaTe
Charges from Dressed Matter: Physics and Renormalisation
Gauge theories are characterised by long range interactions. Neglecting these
interactions at large times, and identifying the Lagrangian matter fields with
the asymptotic physical fields, leads to the infra-red problem. In this paper
we study the perturbative applications of a construction of physical charges in
QED, where the matter fields are combined with the associated electromagnetic
clouds. This has been formally shown, in a companion paper, to include these
asymptotic interactions. It is explicitly demonstrated that the on-shell
Green's functions and S-matrix elements describing these charged fields have,
to all orders in the coupling, the pole structure associated with particle
propagation and scattering. We show in detail that the renormalisation
procedure may be carried out straightforwardly. It is shown that standard
infra-red finite predictions of QED are not altered and it is speculated that
the good infra-red properties of our construction may open the way to the
calculation of previously uncalculable properties. Finally extensions of this
approach to QCD are briefly discussed.Comment: 34 pages, LaTeX, uses FeynMF, 17 figures, very minor wording change,
version to appear in Annals of Physic
Anti-Screening by Quarks and the Structure of the Inter-Quark Potential
The inter-quark potential is dominated by anti-screening effects which
underly asymptotic freedom. We calculate the order g^6 anti-screening
contribution from light fermions and demonstrate that these effects introduce a
non-local divergence. These divergences are shown to make it impossible to
define a coupling renormalisation scheme that renormalises this minimal,
anti-screening potential. Hence the beta function cannot be divided into
screening and anti-screening parts beyond lowest order. However, we then
demonstrate that renormalisation can be carried out in terms of the
anti-screening potential.Comment: 11 pages, some clarifications and typographical corrections, to
appear in Physics Letters
The Glue Around Quarks and the Interquark Potential
The quarks of quark models cannot be identified with the quarks of the QCD
Lagrangian. We review the restrictions that gauge field theories place on any
description of physical (colour) charges. A method to construct charged
particles is presented. The solutions are applied to a variety of applications.
Their Green's functions are shown to be free of infra-red divergences to all
orders in perturbation theory. The interquark potential is analysed and it is
shown that the interaction responsible for anti-screening results from the
force between two separately gauge invariant constituent quarks. A fundamental
limit on the applicability of quark models is identified.Comment: 4 pages, LaTeX, talk given at Montpellier meeting QCD9
Entanglement assisted alignment of reference frames using a dense covariant coding
We present a procedure inspired by dense coding, which enables a highly
efficient transmission of information of a continuous nature. The procedure
requires the sender and the recipient to share a maximally entangled state. We
deal with the concrete problem of aligning reference frames or trihedra by
means of a quantum system. We find the optimal covariant measurement and
compute the corresponding average error, which has a remarkably simple close
form. The connection of this procedure with that of estimating unitary
transformations on qubits is briefly discussed.Comment: 4 pages, RevTeX, Version to appear in PR
Asymptotic Dynamics in Quantum Field Theory
A crucial element of scattering theory and the LSZ reduction formula is the
assumption that the coupling vanishes at large times. This is known not to hold
for the theories of the Standard Model and in general such asymptotic dynamics
is not well understood. We give a description of asymptotic dynamics in field
theories which incorporates the important features of weak convergence and
physical boundary conditions. Applications to theories with three and four
point interactions are presented and the results are shown to be completely
consistent with the results of perturbation theory.Comment: 18 pages, 3 figure
Probing Light Sbottoms with B Decays
We discuss recently reported experimental hints for a bottom squark with mass
around 3.5 GeV decaying as sbottom -> charm + lepton + anti-sneutrino. We
correlate the sbottom lifetime with the decay rates for bottom -> sbottom +
neutrino + anti-sneutrino and bottom -> sbottom + anti-neutrino + sneutrino in
the framework of a minimal supersymmetric model extended by right-handed
(s)neutrinos. Confronting our results with the well-measured semileptonic
branching ratio of B mesons we conclude that the light sbottom interpretation
of the experimental anomalies is ruled out, unless m_bottom < m_sbottom +
m_sneutrino.Comment: 10 pages, 2 figure
How Hard Are the Form Factors in Hadronic Vertices with Heavy Mesons?
The and form factors are evaluated in a full
QCD sum rule calculation. We study the double Borel sum rule for the three
point function of one meson one nucleon and one current up to order
six in the operator product expansion. The double Borel transform is performed
with respect to the nucleon and momenta, and the form factor is
evaluated as a function of the momentum of the heavy meson. These form
factors are relevant to evaluate the charmonium absorption cross section by
hadrons. Our results are compatible with constant form factors in these
vertices.Comment: 12 pages, RevTeX including 5 figures in ps file
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