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\subsection{Cosmology of brane world systems} %Please give
                                                        %title here

{\bf{
{Prof. Dr. Werner Nahm and Dr. Stefan F\"orste}\\
{Physikalisches Institut}\\
{Universit\"at Bonn}\\
{Nussalles 12}\\
{D-53115 BONN}\\
{Telefon: 0228/73-2319}\\
{Fax: 0228/73-3223}\\
{Email: nahm@th.physik.uni-bonn.de}\\}}


\subsubsection{Abstract}

In the last years, the concept of extra space dimensions has
become one of the central research subjects in elementary
particle physics. Guided by the properties of string theories
one is led to the so-called brane worlds, where our universe
might be a multidimenional brane embedded in a higher
dimensional universe. Many particle physics phenomena have been
investigated in this framework, and only recently the comological
properties of such a scheme have been addressed. We would like 
to study the evolution of the universe in this picture with special
emphasis on the questions of the cosmological constant, the 
mechanism of inflation and the asymmetric expansion of spatial
dimensions.

\subsubsection{Current status of research}

Since the work of Horava and Witten on the heterotic M-theory
\cite{horava} the picture of an d=11 dimensional universe
suspended between two d=10 dimensional walls has attracted
much attention. With the concept of D-branes 
\cite{polchinski} this picture can
be generalized and applied to many higher dimensional systems,
and gives new insights in the process of compactifaction of
extra dimensions traditionally discussed in the framework of string
theories. Consequences of this new picture have been worked
out mainly with focus on elementary particle physics. 
Possible implications for cosmology have recently been discussed
as well but are still in a very preliminary stage: for a review
see ref. \cite{binetruy}. 
The observational evidence for a possibly nonvanishing
cosmological constant from supernovae studies enter the
discussion with various schemes of so called 
quintessence. Also here we are just witnessing a first step in
a direction that will be important for any discussion of
cosmological questions in the not so distant future.


\subsubsection{Own experience}

Using our expertise in string theory and compactification
of extra dimensions the group in Bonn has started 
a program to work out possible cosmological consequences
of the new schemes appearing in the so-alled brane
world picture. 

A first application has been the discussion of the cosmological
constant \cite{Lavignac}, where we could clarify some aspects
of higher dimenisional dynamics on the vacuum energy. The
subject has not been clarified yet, as up to now, only a
static model has been given \cite{Lalak}. The generalization
of this picture to an evolving universe should be discussed,
but would need the inclusion of matter on the various
branes. This would then raise the questions of a generalization
of the Friedmann universe to extra dimensions, the
(critical) matter density. As these investigations are still
in a quite early stage, the further development of the field
will strongly depend on the results obtained in the next
year.

This would hopefully shed some light on the question of
a possible successful incorporation of quintessence in
these extra dimensional schemes. First attempts look 
promising, as broken supersymmetry in the bulk
might leave traces as a small cosmological constant on
the wall a possibility that is right now analyzed by our 
group. 



\begin{thebibliography}{99}


\bibitem{horava} P.Horava and E. Witten,
    {\it ``Eleven dimensional supergravity on a manifold with
     boundary''}, {\it
    Nucl.\ Phys.\ } {\bf B475} (1996) 94, {\tt hep-th/9603142}.


\bibitem{polchinski} J. Polchinski, {\it
    ``Dirichlet branes and Ramond-Ramond charges''}, {\it
      Phys. Rev. Lett.} {\bf 75} (1995) 4724, {\tt hep-th/9510017}.

\bibitem{binetruy} 
    P. Binetruy,
    {\it ``New aspects of the cosmology of extra dimensions''}, 
    {\it Int. J. Theor. Phys.} {\bf 38},
    (1999), 2733.

\bibitem{Lavignac} S.\ F\"orste, Z.\ Lalak, S. Lavignac and H.\ P.\ Nilles, 
    {\it ``A comment on self-tuning and vanishing cosmological
    constant in the brane world''}, 
    {\it  Phys. Lett} {\bf B481} (2000) 360, {\tt hep-th/0002164}.

\bibitem{Lalak} S.\ F\"orste, Z.\ Lalak, S. Lavignac and H.\ P.\ Nilles, 
    {\it ``The cosmological constant from a brane world perpective''}, 
    {\it JHEP} {\bf 0009} (2000) 034, {\tt hep-th/0006139}

\end{thebibliography}
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\subsubsection{Goals of the project}

Text needs to be written.





\subsubsection{Estimate of resources expected from DFG}

\begin{itemize}

\item 1 postdoc position 

\item 1 PhD student?

\item travel money 

\item money for invitation

\end{itemize}


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

\begin{itemize}

\item Prof. W. Nahm

\item Dr. s. Foerste

\item Dr. A. Wisskirchen

\item Dr. S. Groot Nibbelink

\item H. Klemm

\end{itemize}


International collaborations with S. Sarkar (Oxford), P. Binetruy
(Paris), M. Quiros (Madrid) and A. Masiero (Trieste).....



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

Connections to work that ...



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