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\subsection{Astrophysics and Extensions of the Standard Model}
                                                        

{\bf{
{Prof. Dr. Herbert Dreiner}\\
{Physikalisches Institut}\\
{Universit\"at Bonn}\\
{Nu{\ss}alle 12}\\
{D-53115 BONN}\\
{Telefon: 0228/73 3432}\\
{Fax: 0228/73 3223}\\
{Email: dreiner@th.physik.uni-bonn.de}\\}}


\subsubsection{Abstract}
I propose to investigate the effects of extensions of the Standard
Model of particle physics on the evolution of the universe. This can
lead to new effects in astrophysics or to bounds on the proposed
extensions. In particular, we would like to focus on the implications
of weak-scale supersymmetry on dark matter, on baryogenesis and
supernovae explosions. We shall also consider the implications of
axions and possible explanations of the ultra-high energy cosmic rays.

\subsubsection{Motivation}

The Standard Model of Particle Physics (SM) has been spectacularly
confirmed by the recently completed experiments at LEP \cite{lep}. It
describes the physics at energies and temperatures upto $200\,GeV$.
Thus in the big bang model the evolution of the universe after the
first ... seconds is described by general relativity and the SM.  We
believe there is physics beyond the SM, which is relevant at energies
and temperatures {\it above} $200\,GeV$.  This new physics, if true,
describes an even earlier epoch of the universe and which could
possibly have profound effects at temperatures below 1 TeV and even
observational effects as late as today. It is our purpose to study the
implications of extensions of the SM on cosmology and astrophysics and
also in reverse the constraints from astrophysics and cosmology on
extensions of the SM.  We shall focus on the the implications of
``low-energy'' particle physics models formulated at or below the GUT
scale of about $10^{16}\,GeV$.

\medskip

The SM has 12 fermions, 12 gauge bosons and 1 scalar Higgs boson.
After the direct detection of the tau neutrino by the DONUT
collaboration \cite{donut} only the Higgs boson remains undetected.
These fields and their interactions are described by 19 parameters
(gauge sector: 3 gauge couplings and one vacuum phase $\theta_{QCD}$
Higgs sector: vacuum expectation value and Higgs mass; fermion sector:
9 masses, 3 mixing angles, 1 CP-violation parameter). Most of these
parameters are very well measured, in particular the lepton and heavy
quark masses as well as the gauge couplings. The light quark masses
are not so well known due to theoretical uncertainties. The mixing
angle between the third generation and the first generation (in the
PDG basis and parametrization) and the CP violating phase are
experimentally poorly determined. These last two measurements will be
dramatically improved by the currently running B-factories, leading to
a stringent test of the SM. If a disagreement with the SM is found, in
particular if the CP-violation is greater than expected then this
would have immediate impact on our understanding of baryogenesis, the
origin of the matter asymmetry in the universe. The Higgs mass of
course remains completely unknown until discovery, hopefully at the
Tevatron or otherwise at the LHC. The experimental full determination
of the Higgs sector will have a similar profound impact. It is one of
the main purposes of this proposal to closely follow these
experimental developments and to regularly explore their implications
for cosmology and astrophysics.

The SM, as presented, has at least 18 open questions, ie the number of
parameters minus one. In particular the spectrum of the fermion
masses, though well measured, remains in its origin a complete
mystery. The Higgs sector has a severe naturalness problem and the
small value of $\theta_{QCD}$ is unexplained in the SM. The proposed
extensions of the SM which could explain these problems all lead to
significant changes in the ``prediction'' for the volution of the
universe. For example, the strong CP-problem can be solved by
introducing an extra $U(1)$ symmetry which when broken is accompanied
by an axion. This axion can significantly contribute to the dark
matter in the universe and can play a crucial r\^{o}le in the
explosion of a supernova. It is the purpose of this project to
investigate the compatibility of extensions of the SM with the present
standard model of cosmology. Here we are mainly interested in (i)
supersymmetry at or below the grand unified scale of $10^{16}\,GeV$,
which solves the naturalness problem of the Higgs sector, (ii) in the
axion, (iii) the electroweak phase transition in extensions of the SM
and (iv) in neutrinos.






\subsubsection{Own Experience}
I have studied in some detail the effect of sphaleron transitions (at
the electroweak phase transition) on GUT-scale baryogenesis in both
the SM and the MSSM \cite{Dreiner:1993vm,Dreiner:1993gg}. In addition,
I have worked extensively on the phenomenology of physics beyond the
Standard Model, in particular on the phenomenology of supersymmetry
\cite{pheno} and of the search for the Higgs boson
\cite{Dittmar:1997ss,Dittmar:1996sp}. Within supersymmetry, I have
mainly focused on supersymmetry with broken R-parity. Combining these
interests, I have determined the bounds on R-parity violating
interactions from the requirement that GUT scale baryogenesis is not
erased before or during the electroweak phase transition.


The SM sphaleron transitions violate baryon- and lepton-number at
temperatures close to or above the electroweak phase transition,
$T\geq T_{EW}$. The sphaleron transitions conserve the three quantum
numbers $\frac{1}{3}{\cal B}-{\cal L}_i$, $i=1,2,3$, where ${\cal B}$
refers to baryon-number and ${\cal L}_i$ to the lepton-number of the
$i$-th family. If the presently observed matter asymmetry is due to
GUT scale matter genesis, one would only expect non-zero contributions
in the quantum numbers $\frac{1}{3}{\cal B}-{\cal L}_i$ to survive for
$T<T_{EW}$. Contributions in $\frac{1}{3}{\cal B}+{\cal L}_i$ should
be erased by the sphaleron transitions. In a detailed chemical
potential analysis, we showed that the non-zero lepton masses below
$T_{EW}$ can regenerate a matter asymmetry even if ${\cal B}-{\cal
  L}=0$ at $T>T_{EW}$. In particular, even ${\cal B}-{\cal L}$ can be
non-zero after the electroweak phase transition. The condition to
achieve this surprising result is that at least one ${\cal L}_i-{\cal
  L}_j\not=0$ at $T>T_{EW}$. Below $T_{EW}$ the leptons have mass.
The number density depends on the mass. Since the masses are different
at $T<T_{EW}$ the cancellation in the number densities no longer holds
and non-zero matter asymmetries are generated. Next we extended this
analysis to supersymmetry where (with conserved $R_p$) where the
effect can be larger due to the larger scalar lepton masses.

\medskip

In the case of R-parity violation no further fields are added beyond
those of the MSSM. However, the superpotential is extended by the
interactions
\begin{equation}
W=\lambda_{ijk}\epsilon_{rs}L^r_iL^s_j{\overline E}_k
+\lambda'_{ijk}\epsilon_{rs}L^r_iQ^s_j{\overline D}_k
+\lambda''_{ijk}\epsilon_{\ell mn}{\overline U}^\ell_i{\overline D}^m_j
{\overline D}^n_k.
\label{eq:rpv}
\end{equation} 
Here $L,{\overline E}$ are the lepton doublet and singlet superfields.
$Q,{\overline U}, {\overline D}$ are the corresponding quark
superfields. $i,j,k$ are generation indices, $r,s$ are $SU(2)$
component indices and $\ell,m,n$ are $SU(3)$ component indices. The
first two sets of terms in Eq.(\ref{eq:rpv}) violate lepton-number,
the last set violates baryon-number.

As discussed above, any extension of the SM (or in this case the MSSM)
has immediate implications for the evolution of the universe. The MSSM
conserves the three quantum numbers $\frac{1}{3}{\cal B}- {\cal L}_i$
as in the SM. If we add further interactions which violate baryon- or
lepton number and these interactions are in thermal equilibrium at
temperatures $T\geq T_{EW}$, then possibly no conserved quantum number
is left and thus no GUT scale baryogenesis may survive. In our paper
we investigaed in detail the conditions under which a GUT scale
baryogenesis {\it does} survive and determined the resulting bounds on
the couplings in Eq.(\ref{eq:rpv}).  If the complete set of
interactions in Eq.(\ref{eq:rpv}) is in thermal equilibrium then any
pre-exisiting matter asymmetry is erased at $T_{EW}$. However, if the
couplings in Eq.(\ref{eq:rpv}) exhibit a similar hierarchy to the
Yukawa couplings in the SM we might expect only a subset to reach
thermal equilibrium. In that case the cosmological bounds on such a
subset can completely vanish and low-energy phenomenology with broken
R-parity is viable. The detailed flavour conditions are determined in
\cite{Dreiner:1993vm,Dreiner:1993gg}.






\subsubsection{Current status of research}

In 1995 the Karmen experiment reported an anomaly in their data, which
was inconsistent with the decay chain $\pi^+\rightarrow\mu^+\nu_\mu
\rightarrow e^+\nu_e\nu_\mu{\bar\nu}_\mu$ as described by the SM
\cite{karmen}. This was at first confirmed by the improved experiment
Karmen II \cite{karmen2}. In a recent paper \cite{Choudhury:2000tn},
we investigated a potential supersymmetric solution of this anomaly: a
very light neutralino ($M_{\chi^0_1}=33.9\,MeV$) decaying via R-parity
violation. Such a neutralino with this specific mass is consistent
with all experiments provided the supersymmetric grand unified
assumption relating the gaugino masses $M_1$ and $M_2$ is
dropped.\footnote{The lower bound on the lightest neutralino from LEP
  $M_{{\tilde\chi}^0_1}\gsim35\,GeV$ is obtained indirectly via the
  experimental search for charginos and the SUSY-GUT gaugino mass
  relation.} As discussed above, when trying to extend the SM to
explain anomalous experimental results one must always take into
consideration the possible astrophysical implications. In this case,
the neutralino is unstable with a cosmologically very short lifetime.
It is thus irrelevant for dark matter studies. However, the neutralino
mass is of the same order as the supernova core temperature and could
thus possibly lead to a too rapid cooling of the core. A rough
estimate \cite{Choudhury:2000tn} based on previous general studies
\cite{Ellis:1988aa} was inconclusive. A further study with a flat (and
too high) core temperature distribution \cite{Kachelriess:2000dz} was
negative.

With the data through July 2000 included, Karmen II no longer confirms
the time anomaly. Together with Peter Richardson, I am now studying
the collider experimental constraints on any neutralino with mass
below a few $GeV$. We will then extend this work to also study the
constraints from supernovae explosions. For this we will include the
proper temperature distribution in the core. This can then be used to
determine the lower mass bound on a light quasi stable neutralino
from supernovae.







\subsubsection{Goals of the project}


\subsubsection{Estimate of resources expected from DFG}


\subsubsection{Members of research group relevant for the project}
\begin{enumerate}
\item Dr. Athansios Dedes (postdoc)
\item Dimitru Ghilencea (postdoc)
\end{enumerate}



\subsubsection{Connections to other projects of current SFB proposal}
can also compute relic density for very light neutralino with non-universal
gaugino masses.

\begin{thebibliography}{99}
  
\bibitem{lep} For the latest results see the web page provided by the
  LEP Electroweak working group:
http://lepewwg.web.cern.ch/LEPEWWG/

%\cite{Dittmar:1997ss}
\bibitem{Dittmar:1997ss}
M.~Dittmar and H.~Dreiner,
%``How to find a Higgs boson with a mass between 155-GeV to 180-GeV 
%at the  LHC,''
Phys.\ Rev.\  {\bf D55} (1997) 167
[hep-ph/9608317].
%%CITATION = HEP-PH 9608317;%%

%\cite{Dittmar:1996sp}
\bibitem{Dittmar:1996sp}
M.~Dittmar and H.~Dreiner,
%``h0 --> W+ W- --> l+ l'- nu/l anti-nu/l' as the dominant SM 
%Higgs  search mode at the LHC for M(h0) = 155-GeV to 180-GeV,''
hep-ph/9703401.
%%CITATION = HEP-PH 9703401;%%

%\cite{Dreiner:1993vm}
\bibitem{Dreiner:1993vm}
H.~Dreiner and G.~G.~Ross,
%``Sphaleron erasure of primordial baryogenesis,''
Nucl.\ Phys.\  {\bf B410} (1993) 188
[hep-ph/9207221].
%%CITATION = HEP-PH 9207221;%%

%\cite{Dreiner:1993gg}
\bibitem{Dreiner:1993gg}
H.~Dreiner,
%``Lepton masses protect the primordial baryogenesis 
%from sphaleron erasure,''
hep-ph/9311286.
%%CITATION = HEP-PH 9311286;%%
%\cite{Choudhury:2000tn}
\bibitem{Choudhury:2000tn}
D.~Choudhury, H.~Dreiner, P.~Richardson and S.~Sarkar,
%``A supersymmetric solution to the KARMEN time anomaly,''
Phys.\ Rev.\  {\bf D61} (2000) 095009
[hep-ph/9911365].
%%CITATION = HEP-PH 9911365;%%

\bibitem{pheno} 
H.~Dreiner, P.~Richardson and M.~H.~Seymour,
%``Resonant slepton production in hadron hadron collisions,''
hep-ph/0007228.

\bibitem{donut}
The seminar presentation at Fermilab is given at\newline
http://fn872.fnal.gov/presentation/complete/2000/WC2000.pdf

\bibitem{karmen}
%\cite{Armbruster:1995nr}
B.~Armbruster {\it et al.}  [KARMEN Collaboration],
%``Anomaly in the time distribution of neutrinos from a pulsed 
%beam stop source,''
Phys.\ Lett.\  {\bf B348} (1995) 19.
%%CITATION = PHLTA,B348,19;%%

\bibitem{karmen2}
B. Zeitnitz, talk given at Neutrino '98, Takayama (1998).

%\cite{Kachelriess:2000dz}
\bibitem{Kachelriess:2000dz}
M.~Kachelriess,
%``The KARMEN anomaly, light neutralinos and supernova SN1987A,''
JHEP {\bf 0002} (2000) 010
[hep-ph/0001160].
%%CITATION = HEP-PH 0001160;%%

%\cite{Ellis:1988aa}
\bibitem{Ellis:1988aa}
J.~Ellis, K.~A.~Olive, S.~Sarkar and D.~W.~Sciama,
%``Low Mass Photinos And Supernova Sn1987a,''
Phys.\ Lett.\  {\bf B215} (1988) 404.
%%CITATION = PHLTA,B215,404;%%

\end{thebibliography}



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