8,494 research outputs found
Consequences of Fine-Tuning for Fifth Force Searches
Light bosonic fields mediate long range forces between objects. If these
fields have self-interactions, i.e., non-quadratic terms in the potential, the
experimental constraints on such forces can be drastically altered due to a
screening (chameleon) or enhancement effect. We explore how technically natural
values for such self-interaction coupling constants modify the existing
constraints. We point out that assuming the existence of these natural
interactions leads to new constraints, contrary to the usual expectation that
screening leads to gaps in coverage. We discuss how screening can turn
fundamentally equivalence principle (EP)-preserving forces into EP-violating
ones. This means that when natural screening is present, searches for EP
violation can be used to constrain EP-preserving forces. We show how this
effect enables the recently discovered stellar triple system \textit{PSR
J03371715} to place a powerful constraint on EP-preserving fifth forces.
Finally, we demonstrate that technically natural cubic self-interactions modify
the vacuum structure of the scalar potential, leading to new constraints from
spontaneous and induced vacuum decay.Comment: 36 pages, 9 figures -- v3 reflects version published in JHE
Nuclear magnetic octupole moment and the hyperfine structure of the states of the Ba ion
The hyperfine structure of the long-lived and levels of
Ba ion is analyzed. A procedure for extracting relatively unexplored
nuclear magnetic moments is presented. The relevant electronic matrix
elements are computed in the framework of the ab initio relativistic many-body
perturbation theory. Both the first- and the second-order (in the hyperfine
interaction) corrections to the energy levels are analyzed. It is shown that a
simultaneous measurement of the hyperfine structure of the entire
fine-structure manifold allows one to extract without contamination
from the second-order corrections. Measurements to the required accuracy should
be possible with a single trapped barium ion using sensitive techniques already
demonstrated in Ba experiments.Comment: Phys Rev A in pres
Eliminating artefacts in polarimetric images using deep learning
Polarization measurements done using Imaging Polarimeters such as the Robotic Polarimeter are very sensitive to the presence of artefacts in images. Artefacts can range from internal reflections in a telescope to satellite trails that could contaminate an area of interest in the image. With the advent of wide-field polarimetry surveys, it is imperative to develop methods that automatically flag artefacts in images. In this paper, we implement a Convolutional Neural Network to identify the most dominant artefacts in the images. We find that our model can successfully classify sources with 98 perβcent true positive and 97 perβcent true negative rates. Such models, combined with transfer learning, will give us a running start in artefact elimination for near-future surveys like WALOP
Stochastic model of optical variability of BL Lacertae
We use optical photometric and polarimetric data of BL Lacertae that cover a
period of 22 years to study the variability of the source. The long-term
observations are employed for establishing parameters of a stochastic model
consisting of the radiation from a steady polarized source and a number of
variable components with different polarization parameters, proposed by
Hagen-Thorn et al. earlier. We infer parameters of the model from the
observations using numerical simulations based on a Monte Carlo method, with
values of each model parameter selected from a Gaussian distribution. We
determine the best set of model parameters by comparing model distributions to
the observational ones using the chi-square criterion. We show that the
observed photometric and polarimetric variability can be explained within a
model with a steady source of high polarization, ~40%, and with direction of
polarization parallel to the parsec scale jet, along with 10+-5 sources of
variable polarization.Comment: 4 pages, 10 figures, published by Astronomy and Astrophysics; v2:
typos correcte
The Use of Music Software Teaching Playing the Drums
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Room-temperature ferromagnetism in nanoparticles of superconducting materials
Nanoparticles of superconducting YBa2Cu3O7-delta (YBCO) (Tc = 91 K) exhibit
ferromagnetism at room temperature while the bulk YBCO, obtained by heating the
nanoparticles at high temperature (940 degree C), shows a linear magnetization
curve. Across the superconducting transition temperature, the magnetization
curve changes from that of a soft ferromagnet to a superconductor. Furthermore,
our experiments reveal that not only nanoparticles of metal oxides but also
metal nitrides such as NbN (Tc = 6 - 12 K) and delta-MoN (Tc ~ 6 K) exhibit
room-temperature ferromagnetism.Comment: 11 pages, 6 figure
Measurement of Lande g factor of 5D5/2 state of BaII with a single trapped ion
We present the first terrestrial measurement of the Lande g factor of the
5D5/2 state of singly ionized barium. Measurements were performed on single
Doppler-cooled 138Ba+ ions in a linear Paul trap. A frequency-stabilized fiber
laser with nominal wavelength 1.762 um was scanned across the 6S1/25D5/2
transition to spectroscopically resolve transitions between Zeeman sublevels of
the ground and excited states. From the relative positions of the four narrow
transitions observed at several different values for the applied magnetic
field, we find a value of 1.2020+/-0.0005 for g of 5D5/2.Comment: 3 figure
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