1,539 research outputs found
Comments on "Limits on possible new nucleon monopole-dipole interactions from the spin relaxation rate of polarized He gas"
In the article "Limits on possible new nucleon monopole-dipole interactions
from the spin relaxation rate of polarized He gas", new limits on
short-range, Axion-like interactions are presented. In this comment it is shown
that the theoretical treatement of the data overestimates the sensitivity of
the proposed method. We provide the corrected limits
Random walks with thermalizing collisions in bounded regions; physical applications valid from the ballistic to diffusive regimes
The behavior of a spin undergoing Larmor precession in the presence of
fluctuating fields is of interest to workers in many fields. The fluctuating
fields cause frequency shifts and relaxation which are related to their power
spectrum, which can be determined by taking the Fourier transform of the
auto-correlation functions of the field fluctuations. Recently we have shown
how to calculate these correlation functions for all values of mean free path
(ballistic to diffusive motion) in finite bounded regions, using the model of
persistent continuous time random walks (CTRW) for particles subject to
scattering by fixed (frozen) scattering centers so that the speed of the moving
particles is not changed by the collisions. In this work we show how scattering
with energy exchange from an ensemble of scatterers in thermal equilibrium can
be incorporated into the CTRW. We present results for 1,2 and 3 dimensions. The
results agree for all these cases contrary to the previously studied 'frozen'
models. Our results for the velocity autocorrelation function show a long time
tail , which we also obtain from conventional
diffusion theory, with the same power, independent of dimensionality. Our
results are valid for any Markovian scattering kernel as well as any kernel
based on a scattering cross section Comment: 43 pages, 12 figure
Search for a new short-range spin-dependent force with polarized Helium 3
Measuring the depolarization rate of a He hyperpolarized gas is a
sensitive method to probe hypothetical short-range spin-dependent forces. A
dedicated experiment is being set up at the Institute Laue Langevin in Grenoble
to improve the sensitivity. We presented the status of the experiment at the
10th PATRAS Workshop on Axions, WIMPs and WISPs.Comment: Presented at the 10th PATRAS Workshop on Axions, WIMPs and WISP
Constraining short-range spin-dependent forces with polarized He
We have searched for a short-range spin-dependent interaction using the spin
relaxation of hyperpolarized He. Such a new interaction would be mediated
by a hypothetical light scalar boson with \CP-violating couplings to the
neutron. The walls of the He cell would generate a pseudomagnetic field and
induce an extra depolarization channel. We did not see any anomalous spin
relaxation and we report the limit for interaction ranges between
and : , where () are the (pseudo)scalar coupling
constant, improving the previous best limit by 1 order of magnitude
Constraining short-range spin-dependent forces with polarized helium 3 at the Laue-Langevin Institute
We have searched for a short-range spin-dependent interaction mediated by a
hypothetical light scalar boson with CP-violating couplings to the neutron
using the spin relaxation of hyperpolarized He. The walls of the He
cell would generate a depolarizing pseudomagnetic field.Comment: Twelfth Conference on the Intersections of Particle and Nuclear
Physics (CIPANP2015), Vail Marriott Mountain Resort, Vail, Colorado, US
Pump-Probe Experiments on the Single-Molecule Magnet Fe8 : Measurement of Excited Level Lifetimes
We present magnetization measurements on the single molecule magnet Fe8 in
the presence of pulsed microwave radiation. A pump-probe technique is used with
two microwave pulses with frequencies of 107 GHz and 118 GHz and pulse lengths
of several nanoseconds to study the spin dynamics via time-resolved
magnetization measurements using a Hall probe magnetometer. We find evidence
for short spin-phonon relaxation times of the order of one microsecond. The
temperature dependence of the spin-phonon relaxation time in our experiments is
in good agreement with previously published theoretical results. We also
established the presence of very short energy diffusion times, that act on a
timescale of about 70 ns.Comment: submitted to Phys. Rev. Lett. (01 March 2007
Observation of strong surface state effects in the nonlinear magneto-optical response of Ni(110)
Spectroscopic magnetization induced optical Second Harmonic Generation (MSHG)
measurements from a clean Ni(110) surface reveal strong resonance effects near
2.7 eV that can be attributed to the presence of an empty surface state. The
good agreement with model calculations shows the potential of MSHG to probe
spin polarized interface band structures.Comment: REVTeX/EPS figures/Authors's single Postsript file, to appear in PRL,
our new phase-sensitive detection technique is used (see PRB, 58, R16020
(1998)), for more details see http://www.sci.kun.nl/tvs/people/petukhov
Size-independence of statistics for boundary collisions of random walks and its implications for spin-polarized gases
A bounded random walk exhibits strong correlations between collisions with a
boundary. For an one-dimensional walk, we obtain the full statistical
distribution of the number of such collisions in a time t. In the large t
limit, the fluctuations in the number of collisions are found to be
size-independent (independent of the distance between boundaries). This occurs
for any inter-boundary distance, including less and greater than the
mean-free-path, and means that this boundary effect does not decay with
increasing system-size. As an application, we consider spin-polarized gases,
such as 3-Helium, in the three-dimensional diffusive regime. The above results
mean that the depolarizing effect of rare magnetic-impurities in the container
walls is orders of magnitude larger than a Smoluchowski assumption (to neglect
correlations) would imply. This could explain why depolarization is so
sensitive to the container's treatment with magnetic fields prior to its use.Comment: 5 page manuscript with extra details in appendices (additional 3
pages
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