788,672 research outputs found

    Precision Tests of Parity Violation Over Cosmological Distances

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    Recent measurements of the Cosmic Microwave Background BB-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-μ\muK 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 >5σ>5\sigma 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 0.050.05^\circ -- an order of magnitude improvement over current CMB polarization calibrators. CalSat-based calibration could be used with current CMB polarimeters searching for BB-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

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    The \phi(\kpp)\sim \kpp relation is called polarization structure. By density functional calculations, we study the polarization structure in ferroelectric perovskite PbTiO3_3, 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 PbTiO3_3 is modified by compressive inplane strains. The bandwidth of polarization dispersion in PbTiO3_3 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 BaTiO3_3 is discussed and compared with that of PbTiO3_3.Comment: 5 Figure

    Polarization of synchrotron emission from relativistic reconfinement shocks

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    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

    A Lack of Resolved Near-Infrared Polarization Across the Face of M51

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    The galaxy M51 was observed using the Mimir instrument on the Perkins telescope to constrain the resolved H-band (1.6 μ\mum) polarization across the galaxy. These observations place an upper limit of PH<0.05P_H<0.05% on the HH-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 HH-band polarization remains undetected. The polarization upper limit at HH-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 (PH/PVRI0.05P_H/P{VRI} \lesssim 0.05) across the face of M51.Comment: 4 pages, 2 figures, Accepted for publication in ApJ

    HST observations of the limb polarization of Titan

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    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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