1,243 research outputs found
Threshold and Flavour Effects in the Renormalization Group Equations of the MSSM II: Dimensionful couplings
We re-examine the one-loop renormalization group equations (RGEs) for the
dimensionful parameters of the minimal supersymmetric Standard Model with
broken supersymmetry, allowing for arbitrary flavour structure of the soft SUSY
breaking (SSB) parameters. We include threshold effects by evaluating the
-functions in a sequence of (non-supersymmetric) effective theories with
heavy particles decoupled at the scale of their mass. We present the most
general form for high scale SSB parameters that obtains if we assume that the
supersymmetry breaking mechanism does not introduce new inter-generational
couplings. This form, possibly amended to allow additional sources of
flavour-violation, serves as a boundary condition for solving the RGEs for the
dimensionful MSSM parameters. We then present illustrative examples of
numerical solutions to the RGEs. We find that in a SUSY GUT with the scale of
SUSY scalars split from that of gauginos and higgsinos, the gaugino mass
unification condition may be violated by (10%). As another
illustration, we show that in mSUGRA, the rate for the flavour-violating
decay obtained using the complete RGE solution is
smaller than that obtained using the commonly-used "single-step" integration of
the RGEs by a factor 10-25, and so may qualitatively change expectations for
topologies from top-squark pair production at colliders. Together with the RGEs
for dimensionless couplings presented in a companion paper, the RGEs in
Appendix B of this paper form a complete set of one-loop MSSM RGEs that include
threshold and flavour-effects necessary for two-loop accuracy.Comment: 96 pages, 14 figures, revtex4, multirow.sty, bm.sty, amsmath.sty;
Corrected Fig. 3 and Eqs. (B9), (B11), (B13) - (B20) and (B24). Results
change by less than 1
Fermion Dipole Moments in Supersymmetric Models with Explicitly Broken R-parity
We present a simple analysis that allows us to extract the leading mass
dependence of the dipole moment of matter fermions that might be induced by new
physics. We present explicit results for the supersymmetric model with broken
R-parity as an illustration. We show that the extra contributions to the
electric dipole moment (edm) of fermions from R-parity violating interactions
can occur only at two loop level, contrary to claims in the literature. We
further find that unlike the generic lepto-quark models, the extra
contributions to the dipole moments of the leptons can only be enhanced by
m_b/m_l and not by m_t/m_l relative to the expectations in the Standard Model.
An interesting feature about this enhancement of these dipole moments is that
it does not involve unknown mixing angles. We then use experimental constraints
on the electric dipole moments of electron and neutron to obtain bounds on (the
imaginary part of) products of R-parity violating couplings, and show that
bounds claimed in the literature are too stringent by many orders of magnitude.Comment: 16 pages latex, 7 figure
Yukawa Coupling Unification in Supersymmetric Models
We present an updated assessment of the viability of t-b-tau Yukawa coupling
unification in supersymmetric models. For the superpotential Higgs mass
parameter mu>0, we find unification to less than 1% is possible, but only for
GUT scale scalar mass parameter m_{16}~8-20 TeV, and small values of gaugino
mass m_{1/2}<400 GeV. Such models require that a GUT scale mass splitting
exists amongst Higgs scalars with m_{H_u}^2<m_{H_d}^2. Viable solutions lead to
a radiatively generated inverted scalar mass hierarchy, with third generation
and Higgs scalars being lighter than other sfermions. These models have very
heavy sfermions, so that unwanted flavor changing and CP violating SUSY
processes are suppressed, but may suffer from some fine-tuning requirements.
While the generated spectra satisfy b->s gamma and (g-2)_mu constraints, there
exists tension with the dark matter relic density unless m_{16}<3 TeV. These
models offer prospects for a SUSY discovery at the Fermilab Tevatron collider
via the search for chargino_1 neutralino_2 -> 3 leptons events, or via gluino
pair production. If mu<0, Yukawa coupling unification to less than 5% can occur
for m_{16} and m_{1/2}>1-2 TeV. Consistency of negative mu Yukawa unified
models with b->s gamma, (g-2)_mu, and relic density all imply very large values
of m_{1/2} typically greater than about 2.5 TeV, in which case direct detection
of sparticles may be a challenge even at the LHC.Comment: 38 pages, 15 figures. Fig.15 changed, some references were added. A
copy of the paper with better resolution figures can be found at
http://www.hep.fsu.edu/~balazs/Physics/Papers/2003
Optimal experimental design for mathematical models of haematopoiesis.
The haematopoietic system has a highly regulated and complex structure in which cells are organized to successfully create and maintain new blood cells. It is known that feedback regulation is crucial to tightly control this system, but the specific mechanisms by which control is exerted are not completely understood. In this work, we aim to uncover the underlying mechanisms in haematopoiesis by conducting perturbation experiments, where animal subjects are exposed to an external agent in order to observe the system response and evolution. We have developed a novel Bayesian hierarchical framework for optimal design of perturbation experiments and proper analysis of the data collected. We use a deterministic model that accounts for feedback and feedforward regulation on cell division rates and self-renewal probabilities. A significant obstacle is that the experimental data are not longitudinal, rather each data point corresponds to a different animal. We overcome this difficulty by modelling the unobserved cellular levels as latent variables. We then use principles of Bayesian experimental design to optimally distribute time points at which the haematopoietic cells are quantified. We evaluate our approach using synthetic and real experimental data and show that an optimal design can lead to better estimates of model parameters
Attempts to identify Cassava Brown Streak Virus in western Democratic Republic of Congo
Open Access ArticleRoot necrosis similar to those of the cassava brown streak disease (CBSD) were observed on cassava in western provinces of the Democratic Republic of Congo (DR.Congo) in the early 2000’s. However molecular laboratory diagnosis were not able to detect any causative agent responsible for the attacks, hence, the disease related to these symptoms was named CBSD-like disease.
In order to assess the distribution and the incidence of the CBSD-like disease, surveys were carried out in four western provinces, comprising, Kwango and Kwilu, Sud Ubangi, Kinshasa and Kongo Central. CBSD-like disease was observed in all surveyed provinces on the basis of root symptoms because foliar symptoms were different to those of the documented cases of CBSD in other parts of east Africa. CBSD-like disease incidence was high in Kongo Central and Sud Ubangi, exceeding an average of 50 %, but low in Kwango and Kwilu (32.8%) and in Kinshasa (19.1%).
During the surveys, cassava leaf samples were collected for lab identification of the causal agent. PCR diagnosis was done on these samples using primers specific for the two known CBSVs. All samples tested negative with no amplification of DNA fragments of the correct size. Thus, further analysis on the causative organism is needed using Next Generation Sequencing (NGS) approaches. NGS approaches will help also to identify the causative organism in other Central Africa countries (Angola, Congo-Brazzaville and Gabon) where such cassava root necrosis have been reported or are suspected
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