651 research outputs found
Particle Candidates of Ultrahigh Energy Cosmic Rays
We discuss candidates for trans-GZK cosmic rays observed in a variety of
detectors. Three types of primaries are represented among the abstracts
submitted to this meeting: neutrin os causing a Z-burst, protons arising from
the decay of ultra-heavy metastable particles and neutrinos within the
framework of low scale string-like models of unification. We attempt to
evaluate the relative merits of these schemes. No definite conclusion can be
reached at this time. However, we point out that some schemes are more
credible/predictive than others. Data to be gathered by the Pierre Auger
observatories as well as orbiting detectors (OWL, Airwatch...) should be able
to decide between the various schemes.Comment: 15 pages, LaTex. Substantially revised to take into account the
discussion at HEP2001, Budapest July 200
Signatures of Precocious Unification in Orbiting Detectors
It has been conjectured that the string and unification scales may be
substantially lower than previously believed, perhaps a few TeV. In scenarios
of this type, orbiting detectors such OWL or AIRWATCH can observe spectacular
phenomena at trans-GZK energies. We explore measurable signatures of the
hypothesis that trans-GZK air showeres (``anomalous showers'') are originated
by strongly interacting neutrinos. The results of a MC simulation of such air
showers is described. A distinction between proton induced and ``anomalous''
showers becomes possible once a substantial sample of trans-GZK showers will be
available.Comment: LaTeX 2e, 14 pages, 5 figures. Revised and expanded version: MC
rerun, figures redrawn, text revised and expande
The robustness of equilibria on convex solids
We examine the minimal magnitude of perturbations necessary to change the
number of static equilibrium points of a convex solid . We call the
normalized volume of the minimally necessary truncation robustness and we seek
shapes with maximal robustness for fixed values of . While the upward
robustness (referring to the increase of ) of smooth, homogeneous convex
solids is known to be zero, little is known about their downward robustness.
The difficulty of the latter problem is related to the coupling (via integrals)
between the geometry of the hull \bd K and the location of the center of
gravity . Here we first investigate two simpler, decoupled problems by
examining truncations of \bd K with fixed, and displacements of with
\bd K fixed, leading to the concept of external \rm and internal \rm
robustness, respectively. In dimension 2, we find that for any fixed number
, the convex solids with both maximal external and maximal internal
robustness are regular -gons. Based on this result we conjecture that
regular polygons have maximal downward robustness also in the original, coupled
problem. We also show that in the decoupled problems, 3-dimensional regular
polyhedra have maximal internal robustness, however, only under additional
constraints. Finally, we prove results for the full problem in case of 3
dimensional solids. These results appear to explain why monostatic pebbles
(with either one stable, or one unstable point of equilibrium) are found so
rarely in Nature.Comment: 20 pages, 6 figure
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