501 research outputs found
Precise bounds on the Higgs boson mass
We study the renormalization group evolution of the Higgs quartic coupling
and the Higgs mass in the Standard Model. The one loop
equation for is non linear and it is of the Riccati type which we
numerically and analytically solve in the energy range where
is the mass of the top quark and GeV. We find that
depending on the value of the solution for
may have singularities or zeros and become negative in the
former energy range so the ultra violet cut off of the standard model should be
below the energy where the zero or singularity of occurs. We find
that for the Standard Model is valid in
the whole range . We consider two cases of the Higgs mass
relation to the parameters of the standard model: (a) the effective potential
method and (b) the tree level mass relations. The limits for
correspond to the following Higgs mass relation GeV. We also plot the dependence of the ultra violet cut
off on the value of the Higgs mass. We analyze the evolution of the vacuum
expectation value of the Higgs field and show that it depends on the value of
the Higgs mass. The pattern of the energy behavior of the VEV is different for
the cases (a) and (b). The behavior of , and
indicates the existence of a phase transition in the standard model. For the
effective potential this phase transition occurs at the mass range
GeV and for the tree level mass relations at GeV.Comment: 14 pages, 7 figures. Expanded the discussion of the Higgs mass
relation between the parameters of the Standard Model. Included the method of
the Higgs effective potentia
Scale dependence of the quark masses and mixings: leading order
We consider the Renormalization Group Equations (RGE) for the couplings of
the Standard Model and its extensions. Using the hierarchy of the quark masses
and of the Cabibbo-Kobayashi-Maskawa (CKM) matrix our argument is that a
consistent approximation for the RGE should be based on the parameter . We consider the RGE in the approximation where we
neglect all the relative terms of the order and higher.
Within this approximation we find the exact solution of the evolution equations
of the quark Yukawa couplings and of the vacuum expectation value of the Higgs
field. Then we derive the evolution of the observables: quark masses, CKM
matrix, Jarlskog invariant, Wolfenstein parameters of the CKM matrix and the
unitarity triangle. We show that the angles of the unitarity triangle remain
constant. This property may restrict the possibility of new symmetries or
textures at the grand unification scale.Comment: 15 pages, 4 figures, author of one reference adde
Quadratic Time-dependent Quantum Harmonic Oscillator
We present a Lie algebraic approach to a Hamiltonian class covering driven,
parametric quantum harmonic oscillators where the parameter set -- mass,
frequency, driving strength, and parametric pumping -- is time-dependent. Our
unitary-transformation-based approach provides a solution to the general
quadratic time-dependent quantum harmonic model. As an example, we show an
analytic solution to the periodically driven quantum harmonic oscillator
without the rotating wave approximation; it works for any given detuning and
coupling strength regime. For the sake of completeness, we provide an analytic
solution to the historical Caldirola--Kanai quantum harmonic oscillator that,
in a suitable reference frame, is just a time-independent parametric quantum
harmonic oscillator.Comment: 22 pages, 4 figure
Detection of West Nile virus-specific antibodies and nucleic acid in horses and mosquitoes, respectively, in Nuevo Leon State, northern Mexico, 2006–2007
Abstract. In the last 5 years, there has been only one reported human case of West Nile virus (WNV) disease in northern Mexico. To determine if the virus was still circulating in this region, equine and entomological surveillance for WNV was conducted in the state of Nuevo Leon in northern Mexico in 2006 and 2007. A total of 203 horses were serologically assayed for antibodies to WNV using an epitope-blocking enzyme-linked immunosorbent assay (bELISA). Seroprevalences for WNV in horses sampled in 2006 and 2007 were 26% and 45%, respectively.
Mosquito collections in 2007 produced 7365 specimens representing 15 species. Culex mosquitoes were screened for WNV RNA and other genera (Mansonia, Anopheles,
Aedes, Psorophora and Uranotaenia) were screened for flaviviruses using reversetranscription (RT)-PCR. Two pools consisting of Culex spp. mosquitoes contained
WNV RNA. Molecular species identification revealed that neither pool included Culex quinquefasciatus (Say) (Diptera:Culicidae) complex mosquitoes. No evidence
of flaviviruses was found in the other mosquito genera examined. These data provide evidence that WNV is currently circulating in northern Mexico and that non-Cx.
quinquefasciatus spp. mosquitoes may be participating in the WNV transmission cycle in this region
Surface energy budget and thermal inertia at Gale Crater: Calculations from ground‐based measurements
The analysis of the surface energy budget (SEB) yields insights into soil‐atmosphere interactions and local climates, while the analysis of the thermal inertia ( I ) of shallow subsurfaces provides context for evaluating geological features. Mars orbital data have been used to determine thermal inertias at horizontal scales of ~10 4 m 2 to ~10 7 m 2 . Here we use measurements of ground temperature and atmospheric variables by Curiosity to calculate thermal inertias at Gale Crater at horizontal scales of ~10 2 m 2 . We analyze three sols representing distinct environmental conditions and soil properties, sol 82 at Rocknest (RCK), sol 112 at Point Lake (PL), and sol 139 at Yellowknife Bay (YKB). Our results indicate that the largest thermal inertia I = 452 J m −2 K −1 s −1/2 (SI units used throughout this article) is found at YKB followed by PL with I = 306 and RCK with I = 295. These values are consistent with the expected thermal inertias for the types of terrain imaged by Mastcam and with previous satellite estimations at Gale Crater. We also calculate the SEB using data from measurements by Curiosity's Rover Environmental Monitoring Station and dust opacity values derived from measurements by Mastcam. The knowledge of the SEB and thermal inertia has the potential to enhance our understanding of the climate, the geology, and the habitability of Mars. Key Points We calculate the thermal inertia and surface energy budget at Gale Crater We use MSL REMS measurements for our calculationsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108664/1/jgre20287.pd
3D characterization of CdSe nanoparticles attached to carbon nanotubes
The crystallographic structure of CdSe nanoparticles attached to carbon
nanotubes has been elucidated by means of high resolution transmission electron
microscopy and high angle annular dark field scanning transmission electron
microscopy tomography. CdSe rod-like nanoparticles, grown in solution together
with carbon nanotubes, undergo a morphological transformation and become
attached to the carbon surface. Electron tomography reveals that the
nanoparticles are hexagonal-based with the (001) planes epitaxially matched to
the outer graphene layer.Comment: 7 pages, 8 figure
The need to promote behaviour change at the cultural level: one factor explaining the limited impact of the MEMA kwa Vijana adolescent sexual health intervention in rural Tanzania. A process evaluation
Background - Few of the many behavioral sexual health interventions in Africa have been rigorously evaluated. Where biological outcomes have been measured, improvements have rarely been found. One of the most rigorous trials was of the multi-component MEMA kwa Vijana adolescent sexual health programme, which showed improvements in knowledge and reported attitudes and behaviour, but none in biological outcomes. This paper attempts to explain these outcomes by reviewing the process evaluation findings, particularly in terms of contextual factors.
Methods - A large-scale, primarily qualitative process evaluation based mainly on participant observation identified the principal contextual barriers and facilitators of behavioural change.
Results - The contextual barriers involved four interrelated socio-structural factors: culture (i.e. shared practices and systems of belief), economic circumstances, social status, and gender. At an individual level they appeared to operate through the constructs of the theories underlying MEMA kwa Vijana - Social Cognitive Theory and the Theory of Reasoned Action – but the intervention was unable to substantially modify these individual-level constructs, apart from knowledge.
Conclusion - The process evaluation suggests that one important reason for this failure is that the intervention did not operate sufficiently at a structural level, particularly in regard to culture. Recently most structural interventions have focused on gender or/and economics. Complementing these with a cultural approach could address the belief systems that justify and perpetuate gender and economic inequalities, as well as other barriers to behaviour change
Multiple glass transitions in star polymer mixtures: Insights from theory and simulations
The glass transition in binary mixtures of star polymers is studied by mode
coupling theory and extensive molecular dynamics computer simulations. In
particular, we have explored vitrification in the parameter space of size
asymmetry and concentration of the small star polymers at
fixed concentration of the large ones. Depending on the choice of parameters,
three different glassy states are identified: a single glass of big polymers at
low and low , a double glass at high and low
, and a novel double glass at high and high which is
characterized by a strong localization of the small particles. At low
and high there is a competition between vitrification and phase
separation. Centered in the -plane, a liquid lake shows up
revealing reentrant glass formation. We compare the behavior of the dynamical
density correlators with the predictions of the theory and find remarkable
agreement between the two.Comment: 15 figures, to be published in Macromolecule
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