173 research outputs found
Universal Limits on Massless High-Spin Particles
We present a model-independent argument showing that massless particles
interacting with gravity in a Minkowski background space can have at most spin
two. This result is proven by extending a famous theorem due to Weinberg and
Witten to theories that do not possess a gauge-invariant stress-energy tensor.Comment: 21 pages. To appear in PRD; two additional reference
On a gauge-invariant interaction of spin-\fth resonances
We show that the gauge-invariant coupling suggested by Pascalutsa removes
non-pole terms from a spin-\fth propagator only for a specific choice of free
parameter. For the general case the problem can be solved by including higher
order derivatives of spin-\fth fields or by modifying the original coupling.
In the latter case the obtained Lagrangian depends on one free parameter
pointing to the freedom in choosing an 'off-shell' content of the theory.
However, the physical observables must not be affected by the 'off-shell'
contributions and should not depend on the free parameter of the Lagrangian
Symmetry Nonrestoration at High Temperature in Little Higgs Models
A detailed study of the high temperature dynamics of the scalar sector of
Little Higgs scenarios, proposed to stabilize the electroweak scale, shows that
the electroweak gauge symmetry remains broken even at temperatures much larger
than the electroweak scale. Although we give explicit results for a particular
modification of the Littlest Higgs model, we expect that the main features are
generic. As a spin-off, we introduce a novel way of dealing with scalar
fluctuations in nonlinear sigma models, which might be of interest for
phenomenological applications.Comment: 23 pages, LaTeX, 4 figure
On the Renormalization of the Complex Scalar Free Field Theory
Polar coordinates are used for the complex scalar free field in D=4
dimensions. The resulting non renormalizable theory is healed by using a
recently proposed symmetric subtraction procedure. The existence of the
coordinates transformation is proved by construction.Comment: 27 pages, no figures, LaTe
The Off-Shell Nucleon-Nucleon Amplitude: Why it is Unmeasurable in Nucleon-Nucleon Bremsstrahlung
Nucleon-nucleon bremsstrahlung has long been considered a way of getting
information about the off-shell nucleon-nucleon amplitude which would allow one
to distinguish among nucleon-nucleon potentials based on their off-shell
properties. There have been many calculations and many experiments devoted to
this aim. We show here, in contrast to this standard view, that such off-shell
amplitudes are not measurable as a matter of principle. This follows formally
from the invariance of the S-matrix under transformations of the fields. This
result is discussed here and illustrated via two simple models, one applying to
spin zero, and one to spin one half, processes. The latter model is very
closely related to phenomenological models which have been used to study
off-shell effects at electromagnetic vertices.Comment: 6 pages, Latex, uses FBSsuppl.cls - Invited plenary talk at the Asia
Pacific Conference on Few Body Problems in Physics, Noda/Kashiwa, Japan,
August, 1999 - To be published in Few Body Systems Supp
Wigner quantum systems (Lie superalgebraic approach)
We present three groups of examples of Wigner Quantum Systems related to the
Lie superalgebras , and and discuss shortly
their physical features. In the case of we indicate that the
underlying geometry is noncommutative.Comment: 8 pages, Latex. to be published in Rep. Math. Phy
The equivalence theorem and the Bethe-Salpeter equation
We solve the Bethe-Salpeter equation for two-particle scattering in a
field-theoretical model using two lagrangians related by a field
transformation. The kernel of the equation consists of the sum of all
tree-level diagrams for each lagrangian. The solutions differ even if all four
external particles are put on the mass shell, which implies that observables
calculated by solving the Bethe-Salpeter equation depend on the representation
of the theory. We point out that this violation of the equivalence theorem has
a simple explanation and should be expected for any Bethe-Salpeter equation
with a tree-level kernel. Implications for dynamical models of hadronic
interactions are discussed.Comment: 10 pages, 4 figures, using REVTeX. Fig. 2 corrected, results
unchanged, to be published in Phys. Lett.
Renormalizability of Nonrenormalizable Field Theories
We give a simple and elegant proof of the Equivalence Theorem, stating that
two field theories related by nonlinear field transformations have the same S
matrix. We are thus able to identify a subclass of nonrenormalizable field
theories which are actually physically equivalent to renormalizable ones. Our
strategy is to show by means of the BRS formalism that the "nonrenormalizable"
part of such fake nonrenormalizable theories, is a kind of gauge fixing, being
confined in the cohomologically trivial sector of the theory.Comment: 3 pages, revtex, no figure
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