2,758 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
Multidimensional hyperbolic billiards
The theory of planar hyperbolic billiards is already quite well developed by
having also achieved spectacular successes. In addition there also exists an
excellent monograph by Chernov and Markarian on the topic. In contrast, apart
from a series of works culminating in Sim\'anyi's remarkable result on the
ergodicity of hard ball systems and other sporadic successes, the theory of
hyperbolic billiards in dimension 3 or more is much less understood. The goal
of this work is to survey the key results of their theory and highlight some
central problems which deserve particular attention and efforts
Characteristic free description of semi-invariants of matrices
A minimal homogeneous generating system of the algebra of semi-invariants of
tuples of two-by-two matrices over an infinite field of characteristic two or
over the ring of integers is given. In an alternative interpretation this
yields a minimal system of homogeneous generators for the vector invariants of
the special orthogonal group of degree four over a field of characteristic two
or over the ring of integers. An irredundant separating system of
semi-invariants of tuples of two-by-two matrices is also determined, it turns
out to be independent of the characteristic.Comment: A crucial reference to a paper of A. Lopatin was adde
- …