8,120 research outputs found
Four Pion Final States with Tagged Photons at Electron Positron Colliders
A Monte Carlo generator has been constructed to simulate the reaction e^+e^-
\to \gamma + 4 \pi, where the photon is assumed to be observed in the detector.
Only initial state radiation is considered. Additional collinear photon
radiation has been incorporated with the technique of structure functions.
Predictions are presented for cms energies of 1GeV, 3GeV and 10GeV,
corresponding to the energies of DAPHNE, BEBC and of B-meson factories. The
event rates are sufficiently high to allow for a precise measurement of R(Q^2)
in the region of Q between approximately 1GeV and 2.5GeV. For the construction
of the program we employ isospin relations between the amplitudes governing tau
decays into four pions and electron positron annihilation into four pions.
Estimates of the kinematic breaking of these isospin relations as a consequence
of the \pi^- -- \pi^0 mass difference are given.Comment: LATEX, 27 pages, 9 figures, discussion of the kinematic breaking of
isospin relations extended, typos corrected, some formulations change
Effects of Economic Interactions on Credit Risk
We study a credit risk model which captures effects of economic interactions
on a firm's default probability. Economic interactions are represented as a
functionally defined graph, and the existence of both cooperative, and
competitive, business relations is taken into account. We provide an analytic
solution of the model in a limit where the number of business relations of each
company is large, but the overall fraction of the economy with which a given
company interacts may be small. While the effects of economic interactions are
relatively weak in typical (most probable) scenarios, they are pronounced in
situations of economic stress, and thus lead to a substantial fattening of the
tails of loss distributions in large loan portfolios. This manifests itself in
a pronounced enhancement of the Value at Risk computed for interacting
economies in comparison with their non-interacting counterparts.Comment: 24 pages, 6 figure
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