J. Carron
University of Sussex
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Featured researches published by J. Carron.
Physical Review D | 2017
J. Peloton; Marcel Schmittfull; Antony Lewis; J. Carron; Oliver Zahn
CMB and lensing reconstruction power spectra are powerful probes of cosmology. However, they are correlated, since the CMB power spectra are lensed, and the lensing reconstruction is constructed using CMB multipoles. We perform a full analysis of the auto- and cross-covariances, including polarization power spectra and minimum-variance lensing estimators, and compare with simulations of idealized future CMBS4 observations. Covariances sourced by fluctuations in the unlensed CMB and instrumental noise can largely be removed by using a realization-dependent subtraction of lensing reconstruction noise, leaving a relatively simple covariance model that is dominated by lensing-induced terms and well described by a small number of principal components. The correlations between the CMB and lensing power spectra will be detectable at the level of ∼5σ for a CMB-S4 mission, and neglecting them could underestimate some parameter error bars by several tens of percent. However, we found that the inclusion of external priors or data sets to estimate parameter error bars can make the impact of the correlations almost negligible.
Physical Review D | 2017
J. Carron; Antony Lewis
Gravitational lensing of the cosmic microwave background (CMB) is a valuable cosmological signal that correlates to tracers of large-scale structure and acts as a important source of confusion for primordial B-mode polarization. State-of-the-art lensing reconstruction analyses use quadratic estimators, which are easily applicable to data. However, these estimators are known to be suboptimal, in particular for polarization, and large improvements are expected to be possible for high signal-to-noise polarization experiments. We develop a method and numerical code, LensIt, that is able to find efficiently the most probable lensing map, introducing no significant approximations to the lensed CMB likelihood, and applicable to beamed and masked data with inhomogeneous noise. It works by iteratively reconstructing the primordial unlensed CMB using a deflection estimate and its inverse, and removing residual lensing from these maps with quadratic estimator techniques. Roughly linear computational cost is maintained due to fast convergence of iterative searches, combined with the local nature of lensing. The method achieves the maximal improvement in signal to noise expected from analytical considerations on the unmasked parts of the sky. Delensing with this optimal map leads to forecast tensor-to-scalar ratio parameter errors improved by a factor ≃2 compared to the quadratic estimator in a CMB stage IV configuration.
Journal of Cosmology and Astroparticle Physics | 2017
J. Carron; Antony Lewis; A. Challinor
arXiv: Cosmology and Nongalactic Astrophysics | 2018
N. Aghanim; Y. Akrami; M. Ashdown; J. Aumont; C. Baccigalupi; M. Ballardini; A. J. Banday; R. B. Barreiro; Nicola Bartolo; S. Basak; K. Benabed; J.-P. Bernard; M. Bersanelli; P. Bielewicz; J. J. Bock; J. Borrill; F. R. Bouchet; F. Boulanger; M. Bucher; C. Burigana; E. Calabrese; J-F Cardoso; J. Carron; A. Challinor; H. C. Chiang; L. P. L. Colombo; C. Combet; B. P. Crill; F. Cuttaia; Paolo de Bernardis