12,649 research outputs found
Effective Lagrangian description of the lepton flavor violating decays Z-->li lj
A comprehensive analysis of the lepton flavor violating (LFV) decays Z-->li
lj is presented within the effective Lagrangian approach. Both the decoupling
and nondecoupling scenarios are explored. The experimental constraints from li
--> lj lk \bar{lk} and li -->lj gamma as well as some relationships arising
from the gauge invariance of the effective Lagrangian are used to put
constraints on Z-->li lj. It is found that while current experimental data
impose very strong constraints on Z-->mu e, the channel Z --> tau mu (e)still
may be at the reach of the planned TESLA collider.Comment: References added, final version to appear in Physical Review
Optimal Paths on the Space-Time SINR Random Graph
We analyze a class of Signal-to-Interference-and-Noise-Ratio (SINR) random
graphs. These random graphs arise in the modeling packet transmissions in
wireless networks. In contrast to previous studies on the SINR graphs, we
consider both a space and a time dimension. The spatial aspect originates from
the random locations of the network nodes in the Euclidean plane. The time
aspect stems from the random transmission policy followed by each network node
and from the time variations of the wireless channel characteristics. The
combination of these random space and time aspects leads to fluctuations of the
SINR experienced by the wireless channels, which in turn determine the
progression of packets in space and time in such a network. This paper studies
optimal paths in such wireless networks in terms of first passage percolation
on this random graph. We establish both "positive" and "negative" results on
the associated time constant. The latter determines the asymptotics of the
minimum delay required by a packet to progress from a source node to a
destination node when the Euclidean distance between the two tends to infinity.
The main negative result states that this time constant is infinite on the
random graph associated with a Poisson point process under natural assumptions
on the wireless channels. The main positive result states that when adding a
periodic node infrastructure of arbitrarily small intensity to the Poisson
point process, the time constant is positive and finite
Rare top quark decays in extended models
Flavor changing neutral currents (FCNC) decays t to H + c, t to Z + c, and H
to t + bar{c} are discussed in the context of Alternative Left-Right symmetric
Models (ALRM) with extra isosinglet heavy fermions where FCNC decays may take
place at tree-level and are only suppressed by the mixing between ordinary top
and charm quarks, which is poorly constraint by current experimental values.
The non-manifest case is also briefly discussed.Comment: Contributed talk given at the 10th Mexican Workhop on Particles and
Fields, Morelia, Michoacan, Mexico, 7-12 Nov 200
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