8,266 research outputs found
On amplitude zeros at threshold
The occurrence of zeros of 2 to n amplitudes at threshold in scalar theories
is studied. We find a differential equation for the scalar potential, which
incorporates all known cases where the 2 to n amplitudes at threshold vanish
for all sufficiently large , in all space-time dimensions, . This
equation is related to the reflectionless potentials of Quantum Mechanics and
to integrable theories in 1+1 dimensions. As an application, we find that the
sine-Gordon potential and its hyperbolic version, the sinh-Gordon potential,
also have amplitude zeros at threshold, , for and
, independently of the mass and the coupling constant.Comment: 6 pages, Latex, CERN-TH.6762/9
Multiscalar production amplitudes beyond threshold
We present exact tree-order amplitudes for , for final states
containing one or two particles with non-zero three-momentum, for various
interaction potentials. We show that there are potentials leading to tree
amplitudes that satisfy unitarity, not only at threshold but also in the above
kinematical configurations and probably beyond. As a by-product, we also
calculate tree amplitudes at threshold and show that for the unbroken
theory they vanish for , for the Standard Model Higgs they
vanish for and for a model potential, respecting tree-order
unitarity, for even and . Finally, we calculate the imaginary part of
the one-loop amplitude in both symmetric and spontaneously broken
theory.Comment: 11 pages, Latex, 3 figures (available on request
(1,0) superconformal theories in six dimensions and Killing spinor equations
We solve the Killing spinor equations of 6-dimensional (1,0) superconformal
theories in all cases. In particular, we derive the conditions on the fields
imposed by the Killing spinor equations and demonstrate that these depend on
the isotropy group of the Killing spinors. We focus on the models proposed by
Samtleben et al in \cite{ssw} and find that there are solutions preserving 1,2,
4 and 8 supersymmetries. We also explore the solutions which preserve 4
supersymmetries and find that many models admit string and 3-brane solitons as
expected from the M-brane intersection rules. The string solitons are smooth
regulated by the moduli of instanton configurations.Comment: 26 page
Zero-dimensional field theory
A study of zero-dimensional theories, based on exact results, is presented.
First, relying on a simple diagrammatic representation of the theory, equations
involving the generating function of all connected Green's functions are
constructed. Second, exact solutions of these equations are obtained for
several theories. Finally, renormalization is carried out. Based on the
anticipated knowledge of the exact solutionsthe full dependence on the
renormalized coupling constant is studied.Comment: 38 pages, LaTe
Recursive actions for scalar theories
We introduce a class of self-interacting scalar theories in which the various
coupling contants obey a recursive relation. These imply a particularly simple
form for the generating function of the Feynman amplitudes with vanishing
external momenta, as well as for the effective potential. In addition we
discuss an interesting duality inherent in these models. Specializing to the
case of zero spacetime dimensions we find intriguing nullification properties
for the amplitudes.Comment: 28 pages, 2 figures Replaced contract numbe
Tsunami hazards in the Eastern Mediterranean: strong earthquakes and tsunamis in the East Hellenic Arc and Trench system
International audienceData on tsunami phenomena occurring in the East Hellenic Arc and Trench system (HA-T) from antiquity up to the present have been updated, critically evaluated and compiled in the standard GITEC format developed in the last decade for the New European Tsunami Catalogue. New field observations are presented for the tsunamis of 9 February 1948 and 24 March 2002. From the 18 tsunamis reported eight are rather well-documented while another nine remain doubtful. The mean recurrence of strong tsunamis is likely equal to about 142 years. Most of the tsunamis documented are caused by strong earthquakes occurring in the area offshore Rhodes to the east or northeast of the island. However, there are large earthquakes near Rhodes that do not cause tsunamis, like the 1926 and 1957 ones, which is of particular importance for the tsunami hazard assessment
Stable Calculations for Unstable Particles: Restoring Gauge Invariance
We discuss theoretical and phenomenological aspects of the use of boson
propagators with energy-dependent widths in predictions for high-energy
scattering processes. In general, gauge invariance is violated in such
calculations. We discuss several approaches to restore gauge invariance,
necessary for a reliable result. The most promising method is the addition of
the relevant parts of the fermionic corrections, which fulfills all Ward
identities. The numerical difference between this and other approaches is
studied. A number of recommendations are given for LEP2 computations.Comment: 13 pages LaTeX inc 1 figure, uses epsf, axodraw. The ps file is
available as ftp://rulgm4.leidenuniv.nl/pub/preprints/stable.ps or on
http://rulgm4.leidenuniv.nl/ under preprints. Added two reference
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