We discuss the phenomenology of the lightest neutralino in models where an effective bilinear term in the superpotential parametrizes the explicit breaking of R-parity. We consider supergravity ...scenarios where the lightest supersymmetric particle (LSP) is the lightest neutralino and which can be explored at LEP2. We present a detailed study of the LSP decay properties and general features of the corresponding signals expected at LEP2. We also contrast our model with gauge mediated supersymmetry breaking.
The two superhard materials diamond and cubic boron nitride, are quite similar in many ways, such as for structure and other properties. Their industrial use is widespread today. A difference of ...major importance for industrial applications is that c-BN — in contrast to diamond — is not dissolved by iron and steel if used as a high duty tool at elevated temperatures. This difference could make c-BN a much more widely usable coating if appropriate low-pressure layer coating technologies could be developed. New findings give some hope in view of achieving this goal.
Since the early successful high-pressure/high-temperature (HPHT) synthesis of diamond in 1955 and cubic boron nitride (c/BN) in 1957 the pressure/temperature phase diagrams were supposed to be quite similar. Recent results — based on calorimetric measurements of combustion enthalpy of c-BN with fluorine — revealed however that in contrast to the diamond/graphite system c-BN — and not h-BN — is the stable phase under standard conditions.
Considering these new facts a comparison between the possibilities of low pressure synthesis of diamond and boron nitride is given. So far the metastable diamond deposition from the gas phase seems however more easy than the formation of the stable c-BN. The main reasons seem to be:
•
• differences in the atomic attachment kinetics during crystal growth, caused by the anisotropy of the c-BN crystals i.e. formation of completely N- or B- terminated facets; as well as
•
• differences of the bonding energies and of the bond lengths of BN, BB, and NN.
Thermodynamic equilibrium calculations for c-BN and h-BN in different gas atmospheres revealed that a selective reaction reducing the formation of the h-BN phase can be expected by addition of excess BCl
3 during a CVD reaction. Preliminary experiments indeed indicated formation of some c-BN together with h-BN, as predicted by the thermodynamic data.
However much further work needs to be done to reach for c-BN a state of the art similar to the today's low-pressure diamond coating technology.
We calculate the supersymmetric
O(
α
s
) QCD corrections to the widths of the Higgs boson decays
H
+ →
t
b
and
H
0, A
0 →
t
t
,
b
b
in the on-shell scheme within the Minimal Supersymmetric Standard ...Model. We find that the QCD corrections are significant, but that the squark pair decay modes are still dominant in a wide parameter region.
The CP violating electric and weak dipole moment form factors of the top quark,
d
γ
(
s) and
d
Z
(
s), appear in the process
e
+e
- → t
t
. We present a complete analysis of these dipole moment form ...factors within the minimal supersymmetric standard model with complex parameters. We include gluino, chargino, and neutralino exchange in the loop of the
γt
t
and Zt
t
vertex. We give the analytic expressions and present numerical results.
High-precision analyses of supersymmetry parameters aim at reconstructing the fundamental supersymmetric theory and its breaking mechanism. A well defined theoretical framework is needed when ...higher-order corrections are included. We propose such a scheme, Supersymmetry Parameter Analysis SPA, based on a consistent set of conventions and input parameters. A repository for computer programs is provided which connect parameters in different schemes and relate the Lagrangian parameters to physical observables at LHC and high energy e + e- linear collider experiments, i.e., masses, mixings, decay widths and production cross sections for supersymmetric particles. In addition, programs for calculating high-precision low energy observables, the density of cold dark matter (CDM) in the universe as well as the cross sections for CDM search experiments are included. The SPA scheme still requires extended efforts on both the theoretical and experimental side before data can be evaluated in the future at the level of the desired precision. We take here an initial step of testing the SPA scheme by applying the techniques involved to a specific supersymmetry reference point.
We report on the electronic and magnetic properties of polypyrrole films with a one-dimensional and two-dimensional microstructure. Polypyrrole films as well defined and stable polymers are studied. ...The aim of this work is an explanation of the macroscopic conductivity based on microscopic and electronic structure. In particular we attribute the high d.c. conductivity, the frequency-independent a.c. conductivity and the weak temperature dependence of the conductivity to the existence of two-dimensional crosslinked areas. We characterize the polypyrrole films by photoelectron spectroscopies (X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS)), by electron paramagnetic resonance (EPR) spectroscopy, and by the frequency- and temperature-dependent conductivity measurements. We compare the results to the corresponding properties of one-dimensional polypyrrole films. The two-dimensional films consist of a graphitic electronic structure in which pyrrole monomers either contribute to the two-dimensional π-system or maintain their monomeric character, as characterized by photoelectron spectroscopies. The EPR data reveal magnetic centers that show a Curie-like susceptibility and a weak Pauli contribution, and the latter does not contribute to the conductivity mechanism. The EPR linewidth is extraordinarily sharp and reversibly reflects the dynamics of the interaction to oxygen.
A
bstract
We calculate the decay width of
h
0
→
b
b
¯
in the Minimal Supersymmetric Standard Model (MSSM) with quark flavour violation (QFV) at full one-loop level. We study the effect of
c
˜
−
t
˜
...mixing and
s
˜
−
b
˜
mixing taking into account the constraints from the B meson data. We discuss and compare in detail the decays
h
0
→
c
c
¯
and
h
0
→
b
b
¯
within the framework of the perturbative mass insertion technique using the Flavour Expansion Theorem. The deviation of both decay widths from the Standard Model values can be quite large. Whereas in
h
0
→
c
c
¯
it is almost entirely due to the flavour violating part of the MSSM, in
h
0
→
b
b
¯
it is mainly due to the flavour conserving part. Nevertheless, the QFV contribution to
Γ
h
0
→
b
b
¯
due to
c
˜
−
t
˜
mixing and chargino exchange can go up to ∼ 7%.
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