44 research outputs found
Grand Unification with Three Generations in Free Fermionic String Models
We examine the problem of constructing three generation free fermionic string
models with grand unified gauge groups. We attempt the construction of models, where is a grand unified group realized at level 1. This
structure allows those Higgs representations to appear which are necessary to
break the symmetry down to the standard model gauge group. For , we
find only models with an even number of generations. However, for we
find a number of 3 generation models.Comment: 22 pages, latex. References added to original versio
The problem, and B and L Conservation with a Discrete Gauge R Symmetry
We examine in a generic context how the problem can be resolved by
means of a spontaneously broken gauge symmetry. We then focus on the new scheme
based on a discrete gauge R symmetry which is spontaneously broken by
nonperturbative hidden sector dynamics triggering supersymmetry breaking also.
The possibility to suppress the dangerous baryon and/or lepton number violating
interactions by means of this discrete R symmetry is examined also together
with some phenomenological consequences.Comment: 13 pages, RevTex, no figure
Anomalous U(1) symmetry and lepton flavor violation
We show that in a large class of models based on anomalous U(1) symmetry
which addresses the fermion mass hierarchy problem, leptonic flavor changing
processes are induced that are in the experimentally interesting range. The
flavor violation occurs through the renormalization group evolution of the soft
SUSY breaking parameters between the string scale and the U(1)_A breaking
scale. We derive general expressions for the evolution of these parameters in
the presence of higher dimensional operators. Several sources for the flavor
violation are identified: flavor-dependent contributions to the soft masses
from the U(1)_A gaugino, scalar mass corrections proportional to the trace of
U(1)_A charge, non-proportional A-terms from vertex corrections, and the U(1)_A
D-term. Quantitative estimates for the decays \mu -> e \gamma and \tau -> \mu
\gamma are presented in supergravity models which accommodate the relic
abundance of neutralino dark matter.Comment: References added, typos corrected, 28 pages LaTeX, includes 14 eps
figure
The b--->s{\gamma} constraint in effective supergravities from string theory
We study the constraints from the decay in the
parameter space of effective supergravities from orbifold string theory and
with minimal supesymmetric particle content. Both the general dilaton-dominated
universal scenario as well as a non-universal scenario for the soft terms are
investigated. It is found that the recently reported CLEO upper and lower
bounds constrain the parameter space of the models under scrutiny. In
particular we find constraints on the values of the parameter and
the gluino masses. In this class of string scenarios the negative sign of the
Higgs mixing parameter , is phenomenologically preferred.Comment: LaTeX 11 pages, figures uuencoded included in a separate file, some
typos have been corrected,1 figure adde
Non-Universal Soft SUSY Breaking and Dark Matter
An analysis is given of the effects of non-universal soft SUSY breaking
masses in the Higgs sector and in the third generation squark sector, and it is
shown that they are highly coupled. Analytic expressions are obtained for their
effects on the parameters and on the third generation squark masses.
Non-universality effects on dark matter event rates in neutralino-nucleus
scattering are analysed. It is found that the effects are maximal in the range
~GeV where the relic density is governed by the Z and
Higgs poles. In this range the minimum event rates can be increased or
decreased by factors of O(10) depending on the sign of non-universality. Above
this range Landau pole effects arising from the heavy top mass tend to suppress
the non-universality effects. The effect of more precise measurements of
cosmological parameters on event rates, which is expected to occur in the next
round of COBE like sattelite experiments, is also investigated. Implications
for the analysis for dark matter searches are discussed.Comment: 28 pages, latex, and 7 fig
A personalized intervention to prevent depression in primary care: cost-effectiveness study nested into a clustered randomized trial
Background: Depression is viewed as a major and increasing public health issue, as it causes high distress in the people experiencing it and considerable financial costs to society. Efforts are being made to reduce this burden by preventing depression. A critical component of this strategy is the ability to assess the individual level and profile of risk for the development of major depression. This paper presents the cost-effectiveness of a personalized intervention based on the risk of developing depression carried out in primary care, compared with usual care. Methods: Cost-effectiveness analyses are nested within a multicentre, clustered, randomized controlled trial of a personalized intervention to prevent depression. The study was carried out in 70 primary care centres from seven cities in Spain. Two general practitioners (GPs) were randomly sampled from those prepared to participate in each centre (i.e. 140 GPs), and 3326 participants consented and were eligible to participate. The intervention included the GP communicating to the patient his/her individual risk for depression and personal risk factors and the construction by both GPs and patients of a psychosocial programme tailored to prevent depression. In addition, GPs carried out measures to activate and empower the patients, who also received a leaflet about preventing depression. GPs were trained in a 10- to 15-h workshop. Costs were measured from a societal and National Health care perspective. Qualityadjustedlife years were assessed using the EuroQOL five dimensions questionnaire. The time horizon was 18 months. Results: With a willingness-to-pay threshold of (sic)10, 000 ((sic)8568) the probability of cost-effectiveness oscillated from 83% (societal perspective) to 89% (health perspective). If the threshold was increased to (sic)30, 000 ((sic)25, 704), the probability of being considered cost-effective was 94% (societal perspective) and 96%, respectively (health perspective). The sensitivity analysis confirmed these results. Conclusions: Compared with usual care, an intervention based on personal predictors of risk of depression implemented by GPs is a cost-effective strategy to prevent depression. This type of personalized intervention in primary care should be further developed and evaluated
Mass predictions based on a supersymmetric SU(5) fixed point
I examine the possibility that the third generation fermion masses are
determined by an exact fixed point of the minimal supersymmetric SU(5) model.
When one-loop supersymmetric thresholds are included, this unified fixed point
successfully predicts the top quark mass, 175 +(-) 2 GeV, as well as the weak
mixing angle. The bottom quark mass prediction is sensitive to the
supersymmetric thresholds; it approaches the measured value for mu <0 and very
large unified gaugino mass. The experimental measurement of the tau lepton mass
determines tan(beta), and the strong gauge coupling and fine structure constant
fix the unification scale and the unified gauge coupling.Comment: 40 pages, 9 figures, 9 tables, Revtex