4,526 research outputs found
Spin-statistics transmutation in relativistic quantum field theories of dyons
We analyse spin and statistics of quantum dyon fields, i.e. fields carrying
both electric and magnetic charge, in 3+1 space-time dimensions. It has been
shown long time ago that, at the quantum mechanical level, a composite dyon
made out of a magnetic pole of charge g and a particle of electric charge e
possesses half-integral spin and fermionic statistics, if the constituents are
bosons and the Dirac quantization condition holds, with n odd. This
phenomenon is called spin-statistics transmutation. We show that the same
phenomenon occurs at the quantum field theory level for an elementary dyon.
This analysis requires the construction of gauge invariant charged dyon fields.
Dirac's proposal for such fields, relying on a Coulomb-like photon cloud, leads
to quantum correlators exhibiting an unphysical dependence on the Dirac-string.
Recently Froehlich and Marchetti proposed a recipe for charged dyon fields,
based on a sum over Mandelstam-strings, which overcomes this problem. Using
this recipe we derive explicit expressions for the quantum field theory
correlators and we provide a proof of the occurrence of spin-statistics
transmutation. The proof reduces to a computation of the self-linking numbers
of dyon worldlines and Mandelstam strings, projected on a fixed time
three-space. Dyon composites are also analysed. The transmutation discussed in
this paper bares some analogy with the appearance of anomalous spin and
statistics for particles or vortices in Chern-Simons theories in 2+1
dimensions. However, peculiar features appear in 3+1 dimensions e.g. in the
spin addition rule.Comment: 32 pages, LaTeX, no figure
Interacting branes, dual branes, and dyonic branes: a unifying lagrangian approach in D dimensions
This paper presents a general covariant lagrangian framework for the dynamics
of a system of closed n-branes and dual (D-n-4)-branes in D dimensions,
interacting with a dynamical (n+1)-form gauge potential. The framework proves
sufficiently general to include also a coupling of the branes to (the bosonic
sector of) a dynamical supergravity theory. We provide a manifestly
Lorentz-invariant and S-duality symmetric Lagrangian, involving the (n+1)-form
gauge potential and its dual (D-n-3)-form gauge potential in a symmetric way.
The corresponding action depends on generalized Dirac-strings. The requirement
of string-independence of the action leads to Dirac-Schwinger quantization
conditions for the charges of branes and dual branes, but produces also
additional constraints on the possible interactions. It turns out that a system
of interacting dyonic branes admits two quantum mechanically inequivalent
formulations, involving inequivalent quantization conditions. Asymmetric
formulations involving only a single vector potential are also given. For the
special cases of dyonic branes in even dimensions known results are easily
recovered. As a relevant application of the method we write an effective action
which implements the inflow anomaly cancellation mechanism for interacting
heterotic strings and five-branes in D=10. A consistent realization of this
mechanism requires, in fact, dynamical p-form potentials and a systematic
introduction of Dirac-strings.Comment: 36 pages, LaTeX, no figure
The cancellation of worldsheet anomalies in the D=10 Green--Schwarz heterotic string sigma--model
We determine the two--dimensional Weyl, Lorentz and --anomalies in
the Green--Schwarz heterotic string sigma--model, in an
-Lorentz covariant background gauge, and prove their cancellation.Comment: 12 pages, Plain TeX, no figure
Dirac Branes, Characteristic Currents and Anomaly Cancellations in 5-Branes
The aim of this note is to discuss, in a somewhat informal language, the
cancellation of anomalies (in topologically trivial space-time) for 5-branes
using as "building blocks": i) a generalization to p-branes of the Dirac
strings of monopoles (Dirac branes) and a refinement of this idea involving a
geometric regularization of Dirac branes, leading to the formalism of
"characteristic currents" ii) the PST formalism . As an example of the
potentiality of the developed framework we discuss in some detail the anomaly
cancellation in the D=10 effective theory of heterotic string and 5-brane
coupled to supergravity, where the anomaly inflow is automatically generated.
Some remarks are also made on a similar approach to the problem of anomaly
cancellation in the effective theory of M5-brane coupled to D=11 supergravity,
developed in collaboration with M.Tonin, where however still as open problem
remains a Dirac anomaly.Comment: LaTeX file, espcrc2.sty, 6 pages. Based on the talk given by P.M. at
the D.V. Volkov Memorial Conference "Supersymmetry and Quantum Field Theory"
(25-29 July, 2000, Kharkov, Ukraine). To be published in Nuclear Physics B
Conference Supplement
Evaluation of Teaching and Learning Strategies
With the growing awareness of the importance of teaching and learning in universities and the need to move towards evidence-based teaching, it behooves the professions to re-examine their educational research methodology. While the what, how and why of student learning have become more explicit, the professions still struggle to find valid methods of evaluating the explosion of new innovation in teaching/learning strategies. This paper discusses the problems inherent in applying traditional experimental design techniques to advances in educational practic
Radiation reaction and four-momentum conservation for point-like dyons
We construct for a system of point-like dyons a conserved energy-momentum
tensor entailing finite momentum integrals, that takes the radiation reaction
into account.Comment: 12 pages, no figure
Immunoreactive inhibin in human follicular fluid in an ovarian hyperstimulation proramme for in vitro fertilisation: correlations and different forms
Chern-kernels and anomaly cancellation in M-theory
This paper deals with magnetic equations of the type dH=J where the current J
is a delta-function on a brane worldvolume and H a p-form field strength. In
many situations in M-theory this equation needs to be solved for H in terms of
a potential. A standard universality class of solutions, involving
Dirac-branes, gives rise to strong intermediate singularities in H which in
many physically relevant cases lead to inconsistencies. In this paper we
present an alternative universality class of solutions for magnetic equations
in terms of Chern-kernels, and provide relevant applications, among which the
anomaly-free effective action for open M2-branes ending on M5-branes. The
unobservability of the Dirac-brane requires a Dirac quantization condition; we
show that the requirement of ``unobservability'' of the Chern-kernel leads in
M-theory to classical gravitational anomalies which cancel precisely their
quantum counterparts.Comment: LaTex, 39 pages, references and comments adde
NS5-branes in IIA supergravity and gravitational anomalies
We construct a gravitational-anomaly-free effective action for the coupled
system of IIA D=10 dynamical supergravity interacting with an NS5-brane. The
NS5-brane is considered as elementary in that the associated current is a
delta-function supported on its worldvolume. Our approach is based on a
Chern-kernel which encodes the singularities of the three-form field strength
near the brane in an SO(4)-invariant way and provides a solution for its
Bianchi identity in terms of a two-form potential. A dimensional reduction of
the recently constructed anomaly-free effective action for an elementary
M5-brane in D=11 is seen to reproduce our ten-dimensional action. The
Chern-kernel approach provides in particular a concrete realization of the
anomaly cancellation mechanism envisaged by Witten.Comment: LaTex, 31 pages, no figure
Ultraviolet singularities in classical brane theory
We construct for the first time an energy-momentum tensor for the
electromagnetic field of a p-brane in arbitrary dimensions, entailing finite
energy-momentum integrals. The construction relies on distribution theory and
is based on a Lorentz-invariant regularization, followed by the subtraction of
divergent and finite counterterms supported on the brane. The resulting
energy-momentum tensor turns out to be uniquely determined. We perform the
construction explicitly for a generic flat brane. For a brane in arbitrary
motion our approach provides a new paradigm for the derivation of the,
otherwise divergent, self-force of the brane. The so derived self-force is
automatically finite and guarantees, by construction, energy-momentum
conservation.Comment: 41 pages, no figures, minor change
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