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, $C_{\ell}$. 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 $C_{\ell}$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 γ-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 γ-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