131 research outputs found
Magnetic interactions and spin dynamics in the bond-disordered pyrochlore fluoride NaCaCoF
We report high-frequency/high-field electron spin resonance (ESR) and
high-field magnetization studies on single crystals of the bond-disordered
pyrochlore NaCaCoF. Frequency- and temperature-dependent ESR
investigations above the freezing temperature K reveal the
coexistence of two distinct magnetic phases. A cooperative paramagnetic phase,
evidenced by a gapless excitation mode, is found as well as a spin-glass phase
developing below 20 K which is associated with a gapped low-energy excitation.
Effective -factors close to 2 are obtained for both modes in line with
pulsed high-field magnetization measurements which show an unsaturated
isotropic behavior up to 58 T at 2 K. In order to describe the field-dependent
magnetization in high magnetic fields, we propose an empirical model accounting
for highly anisotropic ionic -tensors expected for this material and taking
into account the strongly competing interactions between the spins which lead
to a frustrated ground state. As a detailed quantitative relation between
effective -factors as determined from ESR and the local -tensors obtained
by neutron scattering [Ross et al., Phys. Rev. B 93, 014433 (2016)] is still
sought after, our work motivates further theoretical investigations of the
low-energy excitations in bond-disordered pyrochlores.Comment: 9 pages, 6 figure
The X-ray Telescope of CAST
The Cern Axion Solar Telescope (CAST) is in operation and taking data since
2003. The main objective of the CAST experiment is to search for a hypothetical
pseudoscalar boson, the axion, which might be produced in the core of the sun.
The basic physics process CAST is based on is the time inverted Primakoff
effect, by which an axion can be converted into a detectable photon in an
external electromagnetic field. The resulting X-ray photons are expected to be
thermally distributed between 1 and 7 keV. The most sensitive detector system
of CAST is a pn-CCD detector combined with a Wolter I type X-ray mirror system.
With the X-ray telescope of CAST a background reduction of more than 2 orders
off magnitude is achieved, such that for the first time the axion photon
coupling constant g_agg can be probed beyond the best astrophysical constraints
g_agg < 1 x 10^-10 GeV^-1.Comment: 19 pages, 25 figures and images, replaced by the revised version
accepted for publication in New Journal of Physic
First Light Measurements of Capella with the Low Energy Transmission Grating Spectrometer aboard the Chandra X-ray Observatory
We present the first X-ray spectrum obtained by the Low Energy Transmission
Grating Spectrometer (LETGS) aboard the Chandra X-ray Observatory. The spectrum
is of Capella and covers a wavelength range of 5-175 A (2.5-0.07 keV). The
measured wavelength resolution, which is in good agreement with ground
calibration, is 0.06 A (FWHM). Although in-flight
calibration of the LETGS is in progress, the high spectral resolution and
unique wavelength coverage of the LETGS are well demonstrated by the results
from Capella, a coronal source rich in spectral emission lines. While the
primary purpose of this letter is to demonstrate the spectroscopic potential of
the LETGS, we also briefly present some preliminary astrophysical results. We
discuss plasma parameters derived from line ratios in narrow spectral bands,
such as the electron density diagnostics of the He-like triplets of carbon,
nitrogen, and oxygen, as well as resonance scattering of the strong Fe XVII
line at 15.014 A.Comment: 4 pages (ApJ letter LaTeX), 2 PostScript figures, accepted for
publication in ApJ Letters, 200
The microscopic spin-phonon coupling constants in CuGeO_3
Using RPA results, mean field theory, and refined data for the polarization
vectors we determine the coupling constants of the four Peierls-active phonon
modes to the spin chains of CuGeO_3. We then derive the values of the coupling
of the spin system to the linear ionic displacements, the bond lengths and the
angles between bonds. Our values are consistent with microscopic theories and
various experimental results. We discuss the applicability of static approaches
to the spin-phonon coupling. The c-axis anomaly of the thermal expansion is
explained. We give the values of the coupling constants in an effective
one-dimensional Hamiltonian.Comment: 11 pages, two figures, 13 tables, PRB 59 (in press
First results from the CERN Axion Solar Telescope (CAST)
Hypothetical axion-like particles with a two-photon interaction would be
produced in the Sun by the Primakoff process. In a laboratory magnetic field
(``axion helioscope'') they would be transformed into X-rays with energies of a
few keV. Using a decommissioned LHC test magnet, CAST has been running for
about 6 months during 2003. The first results from the analysis of these data
are presented here. No signal above background was observed, implying an upper
limit to the axion-photon coupling < 1.16 10^{-10} GeV^-1 at 95% CL for m_a
<~0.02 eV. This limit is comparable to the limit from stellar energy-loss
arguments and considerably more restrictive than any previous experiment in
this axion mass range.Comment: 4 pages, accepted by PRL. Final version after the referees comment
CAST constraints on the axion-electron coupling
In non-hadronic axion models, which have a tree-level axion-electron interaction, the Sun produces a strong axion flux by bremsstrahlung, Compton scattering, and axiorecombination, the "BCA processes." Based on a new calculation of this flux, including for the first time axio-recombination, we derive limits on the axion-electron Yukawa coupling gae and axion-photon interaction strength ga using the CAST phase-I data (vacuum phase). For ma <~ 10 meV/c2 we find ga gae < 8.1 × 10−23 GeV−1 at 95% CL. We stress that a next-generation axion helioscope such as the proposed IAXO could push this sensitivity into a range beyond stellar energy-loss limits and test the hypothesis that white-dwarf cooling is dominated by axion emission
Search for Dark Matter Axions with CAST-CAPP
The CAST-CAPP axion haloscope, operating at CERN inside the CAST dipole
magnet, has searched for axions in the 19.74 eV to 22.47 eV mass
range. The detection concept follows the Sikivie haloscope principle, where
Dark Matter axions convert into photons within a resonator immersed in a
magnetic field. The CAST-CAPP resonator is an array of four individual
rectangular cavities inserted in a strong dipole magnet, phase-matched to
maximize the detection sensitivity. Here we report on the data acquired for
4124 h from 2019 to 2021. Each cavity is equipped with a fast frequency tuning
mechanism of 10 MHz/min between 4.774 GHz and 5.434 GHz. In the present work,
we exclude axion-photon couplings for virialized galactic axions down to
at the 90% confidence
level. The here implemented phase-matching technique also allows for future
large-scale upgrades.Comment: 24 pages, 5 figures, Published version available with Open Access at
https://www.nature.com/articles/s41467-022-33913-
The mediating role of shared flow and perceived emotional synchrony on compassion for others in a mindful-dancing program
While there is a growing understanding of the relationship between mindfulness and compassion, this largely relates to the form of mindfulness employed in first-generation mindfulness-based interventions such as Mindfulness-Based Stress Reduction. Consequently, there is limited knowledge of the relationship between mindfulness and compassion in respect of the type of mindfulness employed in second-generation mindfulness-based interventions (SG-MBIs), including those that employ the principle of working harmoniously as a “secular sangha.” Understanding this relationship is important because research indicates that perceived emotional synchrony (PES) and shared flow—that often arise during participation in harmonized group contemplative activities—can enhance outcomes relating to compassion, subjective well-being, and group identity fusion. This pilot study analyzed the effects of participation in a mindful-dancing SG-MBI on compassion and investigated the mediating role of shared flow and PES. A total of 130 participants were enrolled into the study that followed a quasi-experimental design with an intervention and control group. Results confirmed the salutary effect of participating in a collective mindful-dancing program, and demonstrated that shared flow and PES fully meditated the effects of collective mindfulness on the kindness and common humanity dimensions of compassion. Further research is warranted to explore whether collective mindfulness approaches, such as mindful dancing, may be a means of enhancing compassion and subjective well-being outcomes due to the mediating role of PES and shared flow.N/
First results of the CAST-RADES haloscope search for axions at 34.67 µeV
We present results of the Relic Axion Dark-Matter Exploratory Setup (RADES), a detector which is part of the CERN Axion Solar Telescope (CAST), searching for axion dark matter in the 34.67 µeV mass range. A radio frequency cavity consisting of 5 sub-cavities coupled by inductive irises took physics data inside the CAST dipole magnet for the first time using this filter-like haloscope geometry. An exclusion limit with a 95% credibility level on the axion-photon coupling constant of ga¿ ¿ 4 × 10-13 GeV-1 over a mass range of 34.6738 µeV < ma< 34.6771 µeV is set. This constitutes a significant improvement over the current strongest limit set by CAST at this mass and is at the same time one of the most sensitive direct searches for an axion dark matter candidate above the mass of 25 µeV. The results also demonstrate the feasibility of exploring a wider mass range around the value probed by CAST-RADES in this work using similar coherent resonant cavities. © 2021, The Author(s)
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