The Lightest Higgs Boson Mass in the Minimal Supersymmetric Standard Model

We compute the upper bound on the mass of the lightest Higgs boson in the Minimal Supersymmetric Standard Model in a model-independent way, including leading (one-loop) and next-to-leading order (two-loop) radiative corrections. We find that (contrary to some recent claims) the two-loop corrections are negative with respect to the one-loop result and relatively small (\simlt 3\%). After defining physical (pole) top quark mass $M_t$, by including QCD self-energies, and physical Higgs mass $M_H$, by including the electroweak self-energies $\Pi\left(M_H^2\right)-\Pi(0)$, we obtain the upper limit on $M_H$ as a function of supersymmetric parameters. We include as supersymmetric parameters the scale of supersymmetry breaking $M_S$, the value of $\tan \beta$ and the mixing between stops $X_t= A_t + \mu \cot\beta$ (which is responsible for the threshold correction on the Higgs quartic coupling). Our results do not depend on further details of the supersymmetric model. In particular, for $M_S\leq 1$ TeV, maximal threshold effect $X_t^2=6M_S^2$ and any value of $\tan\beta$, we find $M_H\leq 140$ GeV for $M_t\leq 190$ GeV. In the particular scenario where the top is in its infrared fixed point we find $M_H\leq 86$ GeV for $M_t = 170$ GeV.Comment: 24 pages + 15 figures in one compressed uuencoded tarred postscript file (The figures can be obtained by e-mail from [email protected]; also, the whole postscript file of the text including the figures can be obtained by ANONYMOUS FTP from ROCA.CSIC.ES (161.111.20.20) at the directory HEP the file being HIGGS.PS: just type GET HEP/HIGGS.PS), Latex, CERN-TH.7334/9

Some Cosmological Implications of Hidden Sectors

We discuss some cosmological implications of extensions of the Standard Model with hidden sector scalars coupled to the Higgs boson. We put special emphasis on the conformal case, in which the electroweak symmetry is broken radiatively with a Higgs mass above the experimental limit. Our refined analysis of the electroweak phase transition in this kind of models strengthens the prediction of a strongly first-order phase transition as required by electroweak baryogenesis. We further study gravitational wave production and the possibility of low-scale inflation as well as a viable dark matter candidate.Comment: 23 pages, 8 figures; some comments added, published versio

Eutrofización de embalses en venezuela : relaciones entre el nitrógeno, el fósforo y la biomasa del fitoplancton

458-475Venezuela has more than 110 oerating reservoirs. However, limnological information is only available for about 20 percent, despite the fact that several of them are subject to negative impacts (eutrophication) caused by anthropogenic activities in their drainage basins. We analyzed the relationships between nutrients and phytoplankton biomass (as chlorophyll a). A total of 14 reservoirs from the north-central and northeastern regions of Venezuela were assessed. The reservoirs showed different degrees of eutrophication, with the most enriched located in unprotected drainage basins. The systems could be separated according to low (less than 20ug/l) and high (grather than 20ug/l) total phosphorus concentrations. Furthermore, in reservoirs with low NO 3:NH 4 ratios, Cyanobacteria were dominant, whereas other phytoplankton groups were dominant in high NO 3:NH 4 ratios. Our results showed a significant linear relationship between chlorophyll a concentrations and nutrients, phosphorus and nitrogen. This is because both nutrients can be limiting for phytoplankton growth, at least in some systems. Following these results, we suggest that the control or mitigation of eutrophication in Venezuelan reservoirs should be based on an improved management of the drainage basins, rather than simply that of the reservoirs themselves

Livestock drought management tool

Final report for project submitted by ILRI to the FAO Sub-Regional Emergency and Rehabilitation Officer for East and Central Africa 10 December 2010In August 2010, the Food and Agriculture Organization (FAO) sub-Regional Emergency Office for Eastern and Central Africa (REOA) contracted the International Livestock Research Institute (ILRI) to develop a proto-type “Livestock Drought Management” (LDM) decision support tool for use by a range of emergency and relief planners and practitioners throughout the region. The tool, which is still conceptual rather than operational, links the concepts of Drought Cycle Management (DCM) with the best practice in livestock-related interventions throughout all phases of a drought, from normal through the alert and emergency stages to recovery. The tool uses data to indicate the severity of the drought (Hazard) and the ability of livestock to survive the drought (sensitivity). The hazard information in the LDM tool is based on Normalized Differential Vegetation Index (NDVI) captured by the NOAA AVHRR system. The tool suggests that the best indicator for sensitivity is livestock body condition (LBC). It combines these two indicators, using expert opinion, to define the phase of the Drought Cycle. The hazard data has currently been parameterized for Kenya, but can be used in any of the REOA countries. At the moment, the missing item is good quality data for sensitivity. Additionally, experts did not agree on how to define the phase of the drought cycle. The tool requires pilot testing in a few local areas before it can be rolled out everywhere

The MSSM from Scherk-Schwarz Supersymmetry Breaking

We present a five-dimensional model compactified on an interval where supersymmetry is broken by the Scherk-Schwarz mechanism. The gauge sector propagates in the bulk, two Higgs hypermultiplets are quasilocalized, and quark and lepton multiplets localized, in one of the boundaries. The effective four-dimensional theory is the MSSM with very heavy gauginos, heavy squarks and light sleptons and Higgsinos. The soft tree-level squared masses of the Higgs sector can be negative and they can (partially) cancel the positive one-loop contributions from the gauge sector. Electroweak symmetry breaking can then comfortably be triggered by two-loop radiative corrections from the top-stop sector. The fine tuning required to obtain the electroweak scale is found to be much smaller than in the MSSM, with essentially no fine-tuning for few TeV gaugino masses. All bounds from direct Higgs searches at LEP and from electroweak precision observables can be satisfied. The lightest supersymmetric particle is a (Higgsino-like) neutralino that can accomodate the abundance of Dark Matter consistently with recent WMAP observations.Comment: 23 pages, 3 figure