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\subsection{Ultra-high energy events in cosmic rays} %Please give title here

{\bf{ 
{Prof. Dr. Peter L. Biermann}\\
{MPIfR and Dept for Physics and Astronomy}\\ 
{Universit\"at Bonn}\\
{Auf dem H{\"u}gel 69}\\
{D-53121 BONN}\\
{Telefon: 0228/525-279}\\
{Fax: 0228/525-229}\\
{Email: plbiermann@mpifr-bonn.mpg.de}\\}}

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%  second version Sep 29, 2000 PeBi, comments from HFA twice
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\subsubsection{Abstract}



\subsubsection{Current status of research}

Ever since the 1960ies cosmic ray events have been observed with an
estimated energy per event of near or above $10^{20}$ eV.  After many
tests and using many new arrays to measure these events in air
fluorescence, in electron/positron airshowres, in muon data underground,
the consensus is indeed that these events are particles coming into the
atmosphere with an energy up to $3 \, 10^{20}$ eV.  With reasonable
values of the galactic magnetic fields, these particles cannot be
contained inside our Galaxy, and so must come from outside.  The best fit
to the data is found with the assumption that these events are protons or
Helium nuclei.  However, in the ubiquitous radiation field of the big
bang, the microwave background, these particles cannot come from farther
than about 50 Mpc real travel distance - since in cosmic magnetic fields
they may be scattered, the real distance of their site of origin may much
closer than this.  Assuming a cosmological distribution of sources,
the resulting spectrum should show a cutoff near $5 \, 10^{19}$ eV, and
this cutoff is absent in the data; however, if the source distribution is
patterned after the galaxy distribution, the discrepancy is much less,
although still there.

There are three classes of proposals how to explain these events:

First, they may be the decay products of more massive particles created
in the big bang, like topological defects, monopoles or the like.  This
proposal has the advantage, that the protons start with $10^{24}$ eV and
so can come from some distance.  However, it follows, that there should
be a strong gamma-ray and neutrino background, a test which will be
possible in the near future.  If there were any correlation with the dark
matter distribution, directional signatures should be there.

Second, it may be due to particles that masquerade as protons, but are
actually something else, like special low mass monopoles or supersymmetric
particles.  This may work if these new hypothetical particles do not
interact with the microwave background, but interact with the atmosphere
hadronically.  Low mass monopoles are a natural choice since the
cosmological magnetic fields easily accelerate monopoles to energies near
and above $10^{21}$ eV.  We will be able to test such ideas if we get
much better statistics and so pointing, because the statistics of arrival
directions, and possible correlations either with the cosmologically
local magnetic field, or with distant quasars should be a tell-tale
signature.  The detailed shower development may also be quite different
between particles such as low mass monopoles, supersymmetric particles and
protons.

Third, these events at the highest energy may due to a single nearby
acceleration site, and then the question is which one:  Radio
galaxies have been suggested, such as Cen A or M87.  For Cen A it is
clear that the source does not have today such an acceleration site, and
so this proposal requires that Cen A was much more powerful at the time
the particles were emitted.  The directional scattering, so as to achieve
near isotropy in arrival directions, is done in the local sheet of the
galaxy distribution in this proposal.  For M87 it has been demonstrated
some time ago, that the source can accelerate protons and Helium nuclei
to the required energy, but then the directional scattering has to be
happen in a Galactic halo wind, quite analogous to the Solar wind.

In all these proposals neutrinos at high energy are produced, which may
be measureable soon as horizontal airshowers.

\subsubsection{Own experience}

Currently Peter L. Biermann is involved in theroetical work with the
various groups which operate air shower arrays, such as AGASA in Japan,
and HIRES in the US, and AUGER (from Germany Karlsruhe is participating
in the construction).

In NRW there is a proposal to build an airshower array across the
country using public buildings such as schools as sites.  Such an array
would not only contribute to public comprehension of basic physics, but
also help to complement the AUGER array, which is in the Southern
hemisphere.   This, however, does require a broad suppoirt in the
community.

Peter L. Biermann is one of the co-proposers (for Germany) of the EUSO
project, an attempt to observe airshowers from space.  This proposal was
accepted for study by both the Astronomy Working Group as well as the
Fundamental Physics Working Group of the European Space Agency, and has
been slated for an accomodation study on the International Space Station.

It would be very useful to work out tests of what EUSO might observe at
the highest energy end, in several PhD theses.  In this work it may be
possible to then determine what happens inside radio galaxies which have a
beam dump site, since there we have particles at $10^{21}$ eV crashing
into a beam dump with a power near to $10^{46}$ erg/s, and a spectrum
which is energetically flat, i.e. $E^{-2}$.  This may lead to new tests
for various newly proposed particles in extensions of particle theory.  

The most recent review by Peter L. Biermann was published at the Puebla
(Mexico) meeting, August 2000.


\subsubsection{Goals of the project}

\subsubsection{Estimate of resources expected from DFG}



\subsubsection{Members of research group relevant for the project}



\subsubsection{Connections to other projects of current SFB proposal}



\subsubsection{Connection to other current research grants}



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