799,247 research outputs found
Precision Tests of Parity Violation Over Cosmological Distances
Recent measurements of the Cosmic Microwave Background -mode polarization
power spectrum by the BICEP2 and POLARBEAR experiments have demonstrated new
precision tools for probing fundamental physics. Regardless of origin, the fact
that we can detect sub-K CMB polarization represents a tremendous
technological breakthrough. Yet more information may be latent in the CMB's
polarization pattern. Because of its tensorial nature, CMB polarization may
also reveal parity-violating physics via a detection of cosmic polarization
rotation. Although current CMB polarimeters are sensitive enough to measure one
degree-level polarization rotation with statistical significance,
they lack the ability to differentiate this effect from a systematic
instrumental polarization rotation. Here, we motivate the search for cosmic
polarization rotation from current CMB data as well as independent radio galaxy
and quasar polarization measurements. We argue that an improvement in
calibration accuracy would allow the precise measurement of parity- and
Lorentz-violating effects. We describe the CalSat space-based polarization
calibrator that will provide stringent control of systematic polarization angle
calibration uncertainties to -- an order of magnitude improvement
over current CMB polarization calibrators. CalSat-based calibration could be
used with current CMB polarimeters searching for -mode polarization,
effectively turning them into probes of cosmic parity violation, i.e. without
the need to build dedicated instruments.Comment: 11 pages, 3 figure
The structure of electronic polarization and its strain dependence
The \phi(\kpp)\sim \kpp relation is called polarization structure. By
density functional calculations, we study the polarization structure in
ferroelectric perovskite PbTiO, revealing (1) the \kpp point that
contributes most to the electronic polarization, (2) the magnitude of
bandwidth, and (3) subtle curvature of polarization dispersion. We also
investigate how polarization structure in PbTiO is modified by compressive
inplane strains. The bandwidth of polarization dispersion in PbTiO is shown
to exhibit an unusual decline, though the total polarization is enhanced. As
another outcome of this study, we formulate an analytical scheme for the
purpose of identifying what determine the polarization structure at arbitrary
\kpp points by means of Wannier functions. We find that \phi(\kpp) is
determined by two competing factors: one is the overlaps between neighboring
Wannier functions within the plane {\it perpendicular} to the polarization
direction, and the other is the localization length {\it parallel} to the
polarization direction. Inplane strain increases the former while decreases the
latter, causing interesting non-monotonous effects on polarization structure.
Finally, polarization dispersion in another paradigm ferroelectric BaTiO is
discussed and compared with that of PbTiO.Comment: 5 Figure
A Lack of Resolved Near-Infrared Polarization Across the Face of M51
The galaxy M51 was observed using the Mimir instrument on the Perkins
telescope to constrain the resolved H-band (1.6 m) polarization across the
galaxy. These observations place an upper limit of on the -band
polarization across the face of M51, at 0.6 arcsecond pixel sampling. Even with
smoothing to coarser angular resolutions, to reduce polarization uncertainty,
the -band polarization remains undetected. The polarization upper limit at
-band, when combined with previous resolved optical polarimetry, rules out a
Serkowski-like polarization dependence on wavelength. Other polarization
mechanisms cannot account for the observed polarization ratio () across the face of M51.Comment: 4 pages, 2 figures, Accepted for publication in ApJ
Polarization of synchrotron emission from relativistic reconfinement shocks
We study the polarization properties of relativistic reconfinement shocks
with chaotic magnetic fields. Using our hydrodynamical model of their
structure, we calculate synthetic polarization maps, longitudinal polarization
profiles and discuss the spatially averaged polarization degree as a function
of jet half-opening angle Theta_j, jet Lorentz factor Gamma_j and observer
inclination angle to the jet axis theta_{obs}. We find, that for theta_{obs} <=
Theta_j the wave electric vectors are parallel in the vicinity of the structure
ends and perpendicular in between, while for theta_{obs} > Theta_j the
polarization can only be perpendicular. The spatially averaged polarization
degree does not exceed 30%. Parallel average polarization, with polarization
degrees lower than 10%, have been found for theta_{obs} < Theta_j under the
condition Gamma_j * Theta_j > 1. As earlier works predicted the parallel
polarization from relativistic conical shocks, we explain our results by
discussing conical shocks with divergent upstream flow.Comment: 8 pages, 10 figures, accepted for publication in MNRA
Stability analysis of polarization attraction in optical fibers
The nonlinear cross-polarization interaction among two intense
counterpropagating beams in a span of lossless randomly birefringent telecom
optical fiber may lead to the attraction an initially polarization scrambled
signal towards wave with a well-defined state of polarization at the fiber
output. By exploiting exact analytical solutions of the nonlinear polarization
coupling process we carry out a linear stability study which reveals that
temporally stable stationary solutions are only obtained whenever the output
signal polarization is nearly orthogonal to the input pump polarization.
Moreover, we predict that polarization attraction is acting in full strength
whenever equally intense signal and pump waves are used
HST observations of the limb polarization of Titan
Titan is an excellent test case for detailed studies of the scattering
polarization from thick hazy atmospheres. We present the first limb
polarization measurements of Titan, which are compared as a test to our limb
polarization models. Previously unpublished imaging polarimetry from the HST
archive is presented which resolves the disk of Titan. We determine
flux-weighted averages of the limb polarization and radial limb polarization
profiles, and investigate the degradation and cancelation effects in the
polarization signal due to the limited spatial resolution of our observations.
Taking this into account we derive corrected values for the limb polarization
in Titan. The results are compared with limb polarization models, using
atmosphere and haze scattering parameters from the literature.
In the wavelength bands between 250 nm and 2000 nm a strong limb polarization
of about 2-7 % is detected with a position angle perpendicular to the limb. The
fractional polarization is highest around 1 micron. As a first approximation,
the polarization seems to be equally strong along the entire limb. The detected
polarization is compatible with expectations from previous polarimetric
observations taken with Voyager 2, Pioneer 11, and the Huygens probe.
Our results indicate that ground-based monitoring measurements of the
limb-polarization of Titan could be useful for investigating local haze
properties and the impact of short-term and seasonal variations of the hazy
atmosphere of Titan. Planets with hazy atmospheres similar to Titan are
particularly good candidates for detection with the polarimetric mode of the
upcoming planet finder instrument at the VLT. Therefore, a good knowledge of
the polarization properties of Titan is also important for the search and
investigation of extra-solar planets.Comment: 13 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
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