62,899 research outputs found
Cosmological Information from Lensed CMB Power Spectra
Gravitational lensing distorts the cosmic microwave background (CMB)
temperature and polarization fields and encodes valuable information on
distances and growth rates at intermediate redshifts into the lensed power
spectra. The non-Gaussian bandpower covariance induced by the lenses is
negligible to l=2000 for all but the B polarization field where it increases
the net variance by up to a factor of 10 and favors an observing strategy with
3 times more area than if it were Gaussian. To quantify the cosmological
information, we introduce two lensing observables, characterizing nearly all of
the information, which simplify the study of non-Gaussian impact, parameter
degeneracies, dark energy models, and complementarity with other cosmological
probes. Information on the intermediate redshift parameters rapidly becomes
limited by constraints on the cold dark matter density and initial amplitude of
fluctuations as observations improve. Extraction of this information requires
deep polarization measurements on only 5-10% of the sky, and can improve Planck
lensing constraints by a factor of ~2-3 on any one of the parameters w_0, w_a,
Omega_K, sum(m_nu) with the others fixed. Sensitivity to the curvature and
neutrino mass are the highest due to the high redshift weight of CMB lensing
but degeneracies between the parameters must be broken externally.Comment: 19 pages, 16 figures, submitted to PR
CMB Lensing Reconstruction on the Full Sky
Gravitational lensing of the microwave background by the intervening dark
matter mainly arises from large-angle fluctuations in the projected
gravitational potential and hence offers a unique opportunity to study the
physics of the dark sector at large scales. Studies with surveys that cover
greater than a percent of the sky will require techniques that incorporate the
curvature of the sky. We lay the groundwork for these studies by deriving the
full sky minimum variance quadratic estimators of the lensing potential from
the CMB temperature and polarization fields. We also present a general
technique for constructing these estimators, with harmonic space convolutions
replaced by real space products, that is appropriate for both the full sky
limit and the flat sky approximation. This also extends previous treatments to
include estimators involving the temperature-polarization cross-correlation and
should be useful for next generation experiments in which most of the
additional information from polarization comes from this channel due to
sensitivity limitations.Comment: Accepted for publication in Phys. Rev. D; typos correcte
Asymmetric Properties of Heat Conduction in a One-Dimensional Frenkel-Kontorova Model
In this Letter, we show numerically that the rectifying effect of heat flux
in a one-dimensional two-segment Frenkel-Kontorova chain demonstrated in recent
literature is merely available under the limit of the weak coupling between the
two constituent segments. Surprisingly, the rectifying effect will be reversed
when the properties of the interface and the system size change. The two types
of asymmetric heat conduction are dominated by different mechanisms, which are
all induced by the nonlinearity. We further discuss the possibility of the
experimental realization of thermal diode or rectifier devices.Comment: 4 Pages, 4 figure
Fragile phase stability in (1-x)Pb(Mg1/3Nb2/3O3)-xPbTiO3 crystals: A comparisons of [001] and [110] field-cooled phase diagrams
Phase diagrams of [001] and [110] field-cooled (FC)
(1-x)Pb(Mg1/3Nb2/3O3)-xPbTiO3 or PMN-xPT crystals have been constructed, based
on high-resolution x-ray diffraction data. Comparisons reveal several
interesting findings. First, a region of abnormal thermal expansion above the
dielectric maximum was found, whose stability range extended to higher
temperatures by application of electric field (E). Second, the rhombohedral (R)
phase of the ZFC state was replaced by a monoclinic MA in the [001] FC diagram,
but with monoclinic MB in the [110] FC. Third, the monoclinic MC phase in ZFC
and [001] FC diagram was replaced by an orthorhombic (O) phase in the [110] FC.
Finally, in the [001] FC diagram, the phase boundary between tetragonal (T) and
MA was extended to lower PT contents (x=0.25); whereas in the [110] FC diagram,
this extended region was entirely replaced by the O phase. These results
clearly demonstrate that the phase stability of PMN-xPT crystals is quite
fragile, depending not only on modest changes in E, but also on the direction
along which that E is applied.Comment: 13 pages, 8 figures, 1 tabl
Multiple phase transitions in single-crystalline NaFeAs
Specific heat, resistivity, susceptibility and Hall coefficient measurements
were performed on high-quality single crystalline NaFeAs. This
compound is found to undergo three successive phase transitions at around 52,
41, and 23 K, which correspond to structural, magnetic and superconducting
transitions, respectively. The Hall effect result indicates the development of
energy gap at low temperature due to the occurrence of spin-density-wave
instability. Our results provide direct experimental evidence of the magnetic
ordering in the nearly stoichiometric NaFeAs.Comment: 4 pages, 4 figure
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