236 research outputs found
Spatial gradients in the cosmological constant
It is possible that there may be differences in the fundamental physical
parameters from one side of the observed universe to the other. I show that the
cosmological constant is likely to be the most sensitive of the physical
parameters to possible spatial variation, because a small variation in any of
the other parameters produces a huge variation of the cosmological constant. It
therefore provides a very powerful {\em indirect} evidence against spatial
gradients or temporal variation in the other fundamental physical parameters,
at least 40 orders of magnitude more powerful than direct experimental
constraints. Moreover, a gradient may potentially appear in theories where the
variability of the cosmological constant is connected to an anthropic selection
mechanism, invoked to explain the smallness of this parameter. In the Hubble
damping mechanism for anthropic selection, I calculate the possible gradient.
While this mechanism demonstrates the existence of this effect, it is too small
to be seen experimentally, except possibly if inflation happens around the
Planck scale.Comment: 12 page
Atom focusing by far-detuned and resonant standing wave fields: Thin lens regime
The focusing of atoms interacting with both far-detuned and resonant standing
wave fields in the thin lens regime is considered. The thin lens approximation
is discussed quantitatively from a quantum perspective. Exact quantum
expressions for the Fourier components of the density (that include all
spherical aberration) are used to study the focusing numerically. The following
lens parameters and density profiles are calculated as functions of the pulsed
field area : the position of the focal plane, peak atomic density,
atomic density pattern at the focus, focal spot size, depth of focus, and
background density. The lens parameters are compared to asymptotic, analytical
results derived from a scalar diffraction theory for which spherical aberration
is small but non-negligible (). Within the diffraction theory
analytical expressions show that the focused atoms in the far detuned case have
an approximately constant background density
while the peak density behaves as , the focal distance or
time as , the focal spot size as
, and the depth of focus as .
Focusing by the resonant standing wave field leads to a new effect, a Rabi-
like oscillation of the atom density. For the far-detuned lens, chromatic
aberration is studied with the exact Fourier results. Similarly, the
degradation of the focus that results from angular divergence in beams or
thermal velocity distributions in traps is studied quantitatively with the
exact Fourier method and understood analytically using the asymptotic results.
Overall, we show that strong thin lens focusing is possible with modest laser
powers and with currently achievable atomic beam characteristics.Comment: 21 pages, 11 figure
To wet or not to wet: that is the question
Wetting transitions have been predicted and observed to occur for various
combinations of fluids and surfaces. This paper describes the origin of such
transitions, for liquid films on solid surfaces, in terms of the gas-surface
interaction potentials V(r), which depend on the specific adsorption system.
The transitions of light inert gases and H2 molecules on alkali metal surfaces
have been explored extensively and are relatively well understood in terms of
the least attractive adsorption interactions in nature. Much less thoroughly
investigated are wetting transitions of Hg, water, heavy inert gases and other
molecular films. The basic idea is that nonwetting occurs, for energetic
reasons, if the adsorption potential's well-depth D is smaller than, or
comparable to, the well-depth of the adsorbate-adsorbate mutual interaction. At
the wetting temperature, Tw, the transition to wetting occurs, for entropic
reasons, when the liquid's surface tension is sufficiently small that the free
energy cost in forming a thick film is sufficiently compensated by the fluid-
surface interaction energy. Guidelines useful for exploring wetting transitions
of other systems are analyzed, in terms of generic criteria involving the
"simple model", which yields results in terms of gas-surface interaction
parameters and thermodynamic properties of the bulk adsorbate.Comment: Article accepted for publication in J. Low Temp. Phy
Threshold criterion for wetting at the triple point
Grand canonical simulations are used to calculate adsorption isotherms of
various classical gases on alkali metal and Mg surfaces. Ab initio adsorption
potentials and Lennard-Jones gas-gas interactions are used. Depending on the
system, the resulting behavior can be nonwetting for all temperatures studied,
complete wetting, or (in the intermediate case) exhibit a wetting transition.
An unusual variety of wetting transitions at the triple point is found in the
case of a specific adsorption potential of intermediate strength. The general
threshold for wetting near the triple point is found to be close to that
predicted with a heuristic model of Cheng et al. This same conclusion was drawn
in a recent experimental and simulation study of Ar on CO_2 by Mistura et al.
These results imply that a dimensionless wetting parameter w is useful for
predicting whether wetting behavior is present at and above the triple
temperature. The nonwetting/wetting crossover value found here is w circa 3.3.Comment: 15 pages, 8 figure
Higgs Boson Physics in the -channel at Colliders
Techniques and strategies for discovering and measuring the properties of
Higgs bosons via -channel production at a collider, and the
associated requirements for the machine and detector, are discussed in detail.
The unique feature of -channel production is that, with good energy
resolution, the mass, total width and partial widths of a Higgs boson can be
directly measured with remarkable accuracy in most cases. For the expected
machine parameters and luminosity the Standard Model (SM) Higgs boson \hsm,
with mass \lsim 2\mw, the light \hl of the minimal supersymmetric Standard
Model (MSSM), and the heavier MSSM Higgs bosons (the CP-odd \ha and the
CP-even \hh) can all be studied in the -channel, with the heavier states
accessible up to the maximal over a large fraction of the MSSM
parameter space. In addition, it may be possible to discover the \ha and
\hh by running the collider at full energy and observing excess events in the
bremsstrahlung tail at lower energy. The integrated luminosity, beam resolution
and machine/detector features required to distinguish between the \hsm and
\hl are delineated.Comment: 87 pages, uuencoded tex file and postscript figure files submitted,
full postscript file, including embedded figures, is available via anonymous
ftp at ftp://ucdhep.ucdavis.edu/gunion/higgs_mupmum.p
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
Fertilization and cover crop effects on soil nitrogen and plant nutrition in a young guarana plantation
Searching for Higgs : From LEP towards LHC
After a brief introduction to the theoretical basis of the Higgs mechanism
for generating the masses of elementary particles, the experimental searches
for Higgs particles will be summarized, from bounds at LEP to inferences for
LHC. The report will focus on the Standard Model, though some central results
on extended Higgs systems, as conjectured for example in supersymmetric
theories, will also be recapitulated. Alternative scenarios based on
spontaneous symmetry breaking by novel strong interactions are adumbrated at
the theoretical level.Comment: Added reference
Dapagliflozin and cardiovascular outcomes in type 2 diabetes
BACKGROUND
The cardiovascular safety profile of dapagliflozin, a selective inhibitor of sodium–
glucose cotransporter 2 that promotes glucosuria in patients with type 2 diabetes,
is undefined.
METHODS
We randomly assigned patients with type 2 diabetes who had or were at risk for atherosclerotic cardiovascular disease to receive either dapagliflozin or placebo. The primary safety outcome was a composite of major adverse cardiovascular events (MACE),
defined as cardiovascular death, myocardial infarction, or ischemic stroke. The primary efficacy outcomes were MACE and a composite of cardiovascular death or hospitalization for heart failure. Secondary efficacy outcomes were a renal composite
(≥40% decrease in estimated glomerular filtration rate to <60 ml per minute per
1.73 m2
of body-surface area, new end-stage renal disease, or death from renal or
cardiovascular causes) and death from any cause.
RESULTS
We evaluated 17,160 patients, including 10,186 without atherosclerotic cardiovascular
disease, who were followed for a median of 4.2 years. In the primary safety outcome
analysis, dapagliflozin met the prespecified criterion for noninferiority to placebo with
respect to MACE (upper boundary of the 95% confidence interval [CI], <1.3; P<0.001
for noninferiority). In the two primary efficacy analyses, dapagliflozin did not result
in a lower rate of MACE (8.8% in the dapagliflozin group and 9.4% in the placebo
group; hazard ratio, 0.93; 95% CI, 0.84 to 1.03; P=0.17) but did result in a lower rate
of cardiovascular death or hospitalization for heart failure (4.9% vs. 5.8%; hazard
ratio, 0.83; 95% CI, 0.73 to 0.95; P=0.005), which reflected a lower rate of hospitalization for heart failure (hazard ratio, 0.73; 95% CI, 0.61 to 0.88); there was no
between-group difference in cardiovascular death (hazard ratio, 0.98; 95% CI, 0.82 to
1.17). A renal event occurred in 4.3% in the dapagliflozin group and in 5.6% in the
placebo group (hazard ratio, 0.76; 95% CI, 0.67 to 0.87), and death from any cause
occurred in 6.2% and 6.6%, respectively (hazard ratio, 0.93; 95% CI, 0.82 to 1.04). Diabetic ketoacidosis was more common with dapagliflozin than with placebo (0.3%
vs. 0.1%, P=0.02), as was the rate of genital infections that led to discontinuation of the
regimen or that were considered to be serious adverse events (0.9% vs. 0.1%, P<0.001).
CONCLUSIONS
In patients with type 2 diabetes who had or were at risk for atherosclerotic cardiovascular disease, treatment with dapagliflozin did not result in a higher or lower rate
of MACE than placebo but did result in a lower rate of cardiovascular death or hospitalization for heart failure, a finding that reflects a lower rate of hospitalization
for heart failure. (Funded by AstraZeneca; DECLARE–TIMI 58 ClinicalTrials.gov
number, NCT01730534.
A search for the decay
We search for the rare flavor-changing neutral-current decay in a data sample of 82 fb collected with the {\sl BABAR}
detector at the PEP-II B-factory. Signal events are selected by examining the
properties of the system recoiling against either a reconstructed hadronic or
semileptonic charged-B decay. Using these two independent samples we obtain a
combined limit of
at the 90% confidence level. In addition, by selecting for pions rather than
kaons, we obtain a limit of using only the hadronic B reconstruction method.Comment: 7 pages, 8 postscript figures, submitted to Phys. Rev. Let
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