8 research outputs found
Effects of a Cut, Lorentz-Boosted sky on the Angular Power Spectrum
The largest fluctuation in the observed CMB temperature field is the dipole,
its origin being usually attributed to the Doppler Effect - the Earth's
velocity with respect to the CMB rest frame. The lowest order boost correction
to temperature multipolar coefficients appears only as a second order
correction in the temperature power spectrum, . Since v/c - 10-3,
this effect can be safely ignored when estimating cosmological parameters
[4-7]. However, by cutting our galaxy from the CMB sky we induce large-angle
anisotropies in the data. In this case, the corrections to the cut-sky
s show up already at first order in the boost parameter. In this
paper we investigate this issue and argue that this effect might turn out to be
important when reconstructing the power spectrum from the cut-sky data.Comment: 12 pages, 1 figur
Real Space Approach to CMB deboosting
The effect of our Galaxy's motion through the Cosmic Microwave Background
rest frame, which aberrates and Doppler shifts incoming photons measured by
current CMB experiments, has been shown to produce mode-mixing in the multipole
space temperature coefficients. However, multipole space determinations are
subject to many difficulties, and a real-space analysis can provide a
straightforward alternative. In this work we describe a numerical method for
removing Lorentz- boost effects from real-space temperature maps. We show that
to deboost a map so that one can accurately extract the temperature power
spectrum requires calculating the boost kernel at a finer pixelization than one
might naively expect. In idealized cases that allow for easy comparison to
analytic results, we have confirmed that there is indeed mode mixing among the
spherical harmonic coefficients of the temperature. We find that using a boost
kernel calculated at Nside=8192 leads to a 1% bias in the binned boosted power
spectrum at l~2000, while individual Cls exhibit ~5% fluctuations around the
binned average. However, this bias is dominated by pixelization effects and not
the aberration and Doppler shift of CMB photons that causes the fluctuations.
Performing analysis on maps with galactic cuts does not induce any additional
error in the boosted, binned power spectra over the full sky analysis. For
multipoles that are free of resolution effects, there is no detectable
deviation between the binned boosted and unboosted spectra. This result arises
because the power spectrum is a slowly varying function of and does not show
that, in general, Lorentz boosts can be neglected for other cosmological
quantities such as polarization maps or higher-point functions.Comment: 8 pages, submitted to MNRA
Effects of Chlorine Mixing on Optoelectronics, Ion-Migration and Gamma-ray Detection In Bromide Perovskites
International audienceControlled anion-mixing in halide perovskites has been shown to be an effective route to precisely tuning optoelectronic properties, in order to achieve efficient photo- voltaic, light emission and radiation detection devices. However, an atomistic under- standing behind the precise mechanism impacting the performances of mixed halide perovskite devices, particularly as a radiation detector, is still missing. Combining high-level computational methods and multiple experiments, here we systematically investigate the effect of chlorine (Cl) incorporation on the optical and electronic prop- erties, structural stability, ion-migration as well as the Îł-ray radiation detection ability of MAPbBr 3-x Cl x . We observe that precise halide mixing suppresses bromide ion mi- gration and consequently reduces the dark current by close to a factor of two, which significantly improves the resistance of the mixed-anion devices. Furthermore, reduced carrier effective masses and mostly unchanged exciton binding energies indicate en- hanced charge carrier transport for these perovskite alloys. At the atomistic level, modifications to ion migration and charge carrier transport properties improve elec- tronic properties and predominantly contribute to the better response and resolution in high-energy Îł-ray detection with MAPbBr 3-x Cl x , as compared to MAPbBr 3 . This study provides a systematic approach to enhance the high-energy radiation detection ability of MAPbBr 3-x Cl x -based devices by understanding the atomistic properties un- derpinning performance