86,601 research outputs found
Muon g-2: Review of Theory and Experiment
A review of the experimental and theoretical determinations of the anomalous
magnetic moment of the muon is given. The anomaly is defined by a=(g-2)/2,
where the Land\'e g-factor is the proportionality constant that relates the
spin to the magnetic moment. For the muon, as well as for the electron and
tauon, the anomaly a differs slightly from zero (of order 10^{-3}) because of
radiative corrections. In the Standard Model, contributions to the anomaly come
from virtual `loops' containing photons and the known massive particles. The
relative contribution from heavy particles scales as the square of the lepton
mass over the heavy mass, leading to small differences in the anomaly for e,
\mu, and \tau. If there are heavy new particles outside the Standard Model
which couple to photons and/or leptons, the relative effect on the muon anomaly
will be \sim (m_\mu/ m_e)^2 \approx 43\times 10^3 larger compared with the
electron anomaly. Because both the theoretical and experimental values of the
muon anomaly are determined to high precision, it is an excellent place to
search for the effects of new physics, or to constrain speculative extensions
to the Standard Model. Details of the current theoretical evaluation, and of
the series of experiments that culminates with E821 at the Brookhaven National
Laboratory are given. At present the theoretical and the experimental values
are known with a similar relative precision of 0.5 ppm. There is, however, a
3.4 standard deviation difference between the two, strongly suggesting the need
for continued experimental and theoretical studyComment: 103 pages, 57 figures, submitted to Reports on Progress in Physics
Final version as published, several minor clarifications to text and a number
of references were correcte
Dynamics of the molecular orientation field coupled to ions in two-dimensional ferroelectric liquid crystals
Molecular orientation fluctuations in ferroelectric smectic liquid crystals
produce space charges, due to the divergence of the spontaneous polarization.
These space charges interact with mobile ions, so that one must consider the
coupled dynamics of the orientation and ionic degrees of freedom. Previous
theory and light scattering experiments on thin free-standing films of
ferroelectric liquid crystals have not included this coupling, possibly
invalidating their quantitative conclusions. We consider the most important
case of very slow ionic dynamics, compared to rapid orientational fluctuations,
and focus on the use of a short electric field pulse to quench orientational
fluctuations. We find that the resulting change in scattered light intensity
must include a term due to the quasistatic ionic configuration, which has
previously been ignored. In addition to developing the general theory, we
present a simple model to demonstrate the role of this added term
The Physics Case for the New Muon (g-2) Experiment
This White Paper briefly reviews the present status of the muon (g-2)
experiment and the physics motivation for a new effort. The present comparison
between experiment and theory indicates a tantalizing deviation.
An improvement in precision on this comparison by a factor of 2--with the
central value remaining unchanged--will exceed the ``discovery'' threshold,
with a sensitivity above . The 2.5-fold reduction improvement goal of
the new Brookhaven E969 experiment, along with continued steady reduction of
the standard model theory uncertainty, will achieve this more definitive test.
Already, the (g-2) result is arguably the most compelling indicator of
physics beyond the standard model and, at the very least, it represents a major
constraint for speculative new theories such as supersymmetry or extra
dimensions. In this report, we summarize the present experimental status and
provide an up-to-date accounting of the standard model theory, including the
expectations for improvement in the hadronic contributions, which dominate the
overall uncertainty. Our primary focus is on the physics case that motivates
improved experimental and theoretical efforts. Accordingly, we give examples of
specific new-physics implications in the context of direct searches at the LHC
as well as general arguments about the role of an improved (g-2) measurement. A
brief summary of the plans for an upgraded effort complete the report.Comment: 18 pages, 7 figure
Role of electrostatics in the texture of islands in free standing ferroelectric liquid crystal films
Curved textures of ferroelectric smectic C* liquid crystals produce space
charge when they involve divergence of the spontaneous polarization field.
Impurity ions can partially screen this space charge, reducing long range
interactions to local ones. Through studies of the textures of islands on very
thin free-standing smectic films, we see evidence of this effect, in which
materials with a large spontaneous polarization have static structures
described by a large effective bend elastic constant. To address this issue, we
calculated the electrostatic free energy of a free standing film of
ferroelectric liquid crystal, showing how the screened coulomb interaction
contributes a term to the effective bend elastic constant, in the static long
wavelength limit. We report experiments which support the main features of this
model
Coarse-grained reconfigurable array architectures
Coarse-Grained Reconfigurable Array (CGRA) architectures accelerate the same inner loops that benefit from the high ILP support in VLIW architectures. By executing non-loop code on other cores, however, CGRAs can focus on such loops to execute them more efficiently. This chapter discusses the basic principles of CGRAs, and the wide range of design options available to a CGRA designer, covering a large number of existing CGRA designs. The impact of different options on flexibility, performance, and power-efficiency is discussed, as well as the need for compiler support. The ADRES CGRA design template is studied in more detail as a use case to illustrate the need for design space exploration, for compiler support and for the manual fine-tuning of source code
The H Beta Index as an Age Indicator of Old Stellar Systems: The Effects of Horizontal-Branch Stars
The strength of the H index has been computed for the integrated
spectra of model globular clusters from the evolutionary population synthesis.
These models take into account, for the first time, the detailed systematic
variation of horizontal-branch (HB) morphology with age and metallicity. Our
models show that the H index is significantly affected by the presence
of blue HB stars. Because of the contribution from blue HB stars, the H
does not monotonically decrease as metallicity increases at a given age.
Instead, it reaches a maximum strength when the distribution of HB stars is
centered around 9500 K, the temperature where the H index becomes
strongest. Our models indicate that the strength of the H index
increases as much as 0.75 {\AA} due to the presence of blue HB stars.
The comparison of the recent Keck observations of the globular cluster system
in the Milky Way Galaxy with those in giant elliptical galaxies, NGC 1399 and
M87, shows a systematic shift in the H against metallicity plane. Our
models suggest that this systematic difference is understood if the globular
cluster systems in giant elliptical galaxies are several billion years older,
in the mean, than the Galactic counterpart. Further observations of globular
cluster systems in the external galaxies from the large ground-based telescopes
and space UV facilities will enable to clarify whether this difference is
indeed due to the age difference or other explanations are also possible.Comment: 21 pages, 8 figures, Accepted for publication in the Astronomical
Journal, August 2000 issue, Postscript files are available at
http://csaweb.yonsei.ac.kr/~hclee/Hbet
Type I background fields in terms of type IIB ones
We choose such boundary conditions for open IIB superstring theory which
preserve N=1 SUSY. The explicite solution of the boundary conditions yields
effective theory which is symmetric under world-sheet parity transformation
. We recognize effective theory as closed type I
superstring theory. Its background fields,beside known even fields of
the initial IIB theory, contain improvements quadratic in odd ones.Comment: 4 revtex pages, no figure
Bio-inspired Tensegrity Soft Modular Robots
In this paper, we introduce a design principle to develop novel soft modular
robots based on tensegrity structures and inspired by the cytoskeleton of
living cells. We describe a novel strategy to realize tensegrity structures
using planar manufacturing techniques, such as 3D printing. We use this
strategy to develop icosahedron tensegrity structures with programmable
variable stiffness that can deform in a three-dimensional space. We also
describe a tendon-driven contraction mechanism to actively control the
deformation of the tensegrity mod-ules. Finally, we validate the approach in a
modular locomotory worm as a proof of concept.Comment: 12 pages, 7 figures, submitted to Living Machine conference 201
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