1,091 research outputs found
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 , by including QCD
self-energies, and physical Higgs mass , by including the electroweak
self-energies , we obtain the upper limit on
as a function of supersymmetric parameters. We include as supersymmetric
parameters the scale of supersymmetry breaking , the value of
and the mixing between stops (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
TeV, maximal threshold effect and any value of
, we find GeV for GeV. In the particular
scenario where the top is in its infrared fixed point we find GeV
for 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
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
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
The Mixmaster Spacetime, Geroch's Transformation and Constants of Motion
We show that for -symmetric spacetimes on a constant of
motion associated with the well known Geroch transformation, a functional
, quadratic in gravitational momenta, is strictly positive
in an open subset of the set of all -symmetric initial data, and
therefore not weakly zero. The Mixmaster initial data appear to be on the
boundary of that set. We calculate the constant of motion perturbatively for
the Mixmaster spacetime and find it to be proportional to the minisuperspace
Hamiltonian to the first order in the Misner anisotropy variables, i.e. weakly
zero. Assuming that is exactly zero for the Mixmaster spacetime, we show
that Geroch's transformation, when applied to the Mixmaster spacetime, gives a
new \mbox{-symmetric} solution of the vacuum Einstein equations, globally
defined on \mbox{},which is non-homogeneous and
presumably exhibits Mixmaster-like complicated dynamical behavior.Comment: 25 pages, preprint YCTP-20-93, Revte
A Bayesian model for anchovy (Engraulis encrasicolus): the combined forcing of man and environment
Fishery collapses frequently result from combined
pressures of the environment and man, which are
difficult to discern because of the complexities
involved and our limited knowledge. Models to resolve
this complexity often become too sophisticated,
with too many assumptions and, consequently, with
little capacity to predict beyond calibration data. In
this paper we implement a different procedure where
the model is kept simple and uncertainty accounts for
the equation imperfectness to reproduce ecological
complexity. Human and environmental forcing on an
anchovy (Engraulis encrasicolus) stock are simulated
with only six parameters plus their error terms, and
the uncertainty is computed with Bayesian methods.
The simple structure is able to reproduce the major
dynamical features of this species in the Gulf of
Ca´diz, including data on life stages and age structure
that had no contact with the model. This is a distinct
performance for a frugal approach working on a
mid-trophic species and a positive instance where
parsimony can simulate the interaction of man,
fish and the environment, provided uncertainty is
accounted for in the process.Publicado
Synthesis, Structure and Antitumour Properties of a New 1,2-Propylenediaminetetraacetate-Ruthenium(III) Compound
A novel complex formed by ruthenium (III) and the sequestering ligand
1,2-propylenediaminetetraacetic acid (PDTA) has been synthetized and characterized. The structure
of the monomeric compound, studied by X-ray diffraction , shows an almost symmetric octahedral
geometry around the metal ion, with two chlorine atoms in a cis conformation. The antitumour
activity against a variety of murine and human cancers is reported
Finite Higgs mass without Supersymmetry
We identify a class of chiral models where the one-loop effective potential
for Higgs scalar fields is finite without any requirement of supersymmetry. It
corresponds to the case where the Higgs fields are identified with the
components of a gauge field along compactified extra dimensions. We present a
six dimensional model with gauge group U(3)xU(3) and quarks and leptons
accomodated in fundamental and bi-fundamental representations. The model can be
embedded in a D-brane configuration of type I string theory and, upon
compactification on a T^2/Z_2 orbifold, it gives rise to the standard model
with two Higgs doublets.Comment: 28 pages, 4 figures, uses axodraw. Some typos corrected and
references rearrange
Covalent Cross-Linking of 2H-MoS2 Nanosheets
The combination of 2D materials opens a wide range of possibilities to create new-generation structures with multiple applications. Covalently cross-linked approaches are a ground-breaking strategy for the formation of homo or heterostructures made by design. However, the covalent assembly of transition metal dichalcogenides flakes is relatively underexplored. Here, a simple covalent cross-linking method to build 2H-MoS2–MoS2 homostructures is described, using commercially available bismaleimides. These assemblies are mainly connected vertically, basal plane to basal plane, creating specific molecular sized spaces between MoS2 sheets. Therefore, this straightforward approach gives access to the controlled connection of sulfide-based 2D materials
- …