@article{1994b4f1d4ea495cb93bf13466eb9de7,
title = "Revised estimates of CMB B-mode polarization induced by patchy reionization",
abstract = "The search for primordial gravitational waves through the B-mode polarization pattern in the CMB is one of the major goals of current and future CMB experiments. Besides foregrounds, a potential hurdle in this search is the anisotropic secondary B-mode polarization generated by the scattering of CMB photons off free electrons produced during patchy cosmological reionization. Robust predictions of these secondary anisotropies are challenging because of uncertainties in the reionization history. In this paper we revise estimates of the reionization-induced B-mode signal by incorporating recent advances in the understanding of reionization through observations of the Lyman-α forest. To derive these B-mode estimates, we use high-dynamic-range radiative transfer simulations of reionization that are calibrated to the Lyα data. These simulations are also consistent with a variety of other high-redshift observations. We find that around multipoles ` ≈ 100, reionization induces B-mode power with `(` + 1)C`BB/2π ≈ 4 × 10−6 µK2. This secondary signal is thus at the level of the primordial signal with the tensor-to-scalar ratio r < 10−4, and can increase by a factor of ∼ 50 if reionization is sourced by highly clustered sources residing in haloes with mass of ∼ 1011 M⊙. Our findings suggest that the contribution of patchy reionization to the search for primordial gravitational waves is unlikely to be a concern for currently planned CMB experiments.",
keywords = "CMBR experiments, Gravitational waves and CMBR polarization, Lyman alpha forest, Reionization",
author = "Anirban Roy and Girish Kulkarni and {Daniel Meerburg}, P. and Anthony Challinor and Carlo Baccigalupi and Andrea Lapi and Haehnelt, {Martin G.}",
note = "Funding Information: AR would like to thank the Kavli Institute for Cosmology Cambridge (KICC) for hospitality during the early phases of this project. The authors would like to thank Marcelo Alvarez, Nicholas Battaglia, Tirthankar Roy Choudhury, Cora Dvorkin, Rishi Khatri, Ranjan Modak, David Spergel, and Matteo Viel for useful discussions. The results presented in the paper relied on the Cambridge Service for Data Driven Discovery (CSD3) operated by the University of Cambridge (www.csd3.cam.ac.uk), provided by Dell EMC and Intel using Tier-2 funding from the Engineering and Physical Sciences Research Council (capital grant EP/P020259/1), and DiRAC funding from the Science and Technology Facilities Council (www.dirac.ac.uk). This work further used the COSMA Data Centric system operated Durham University on behalf of the STFC DiRAC HPC Facility. This equipment was funded by a BIS National E-infrastructure capital grant ST/K00042X/1, DiRAC Operations grant ST/K003267/1 and Durham University. DiRAC is part of the National E-Infrastructure. This work is partially supported by PRIN MIUR 2015 grant {\textquoteleft}Cosmology and Fundamental Physics: illuminating the Dark Universe with Euclid{\textquoteright}, PRIN INAF 2014 grant {\textquoteleft}Probing the AGN/galaxy co-evolution through ultra-deep and ultra-high-resolution radio surveys{\textquoteright}, the MIUR grant {\textquoteleft}Finanziamento annuale individuale attivita base di ricerca{\textquoteright} and the RADIO-FOREGROUNDS grant (COMPET-05-2015, agreement number 687312) of the European Union Horizon 2020 research and innovation program. PDM acknowledges support from a Kavli Institute Senior Fellowship at the University of Cambridge and the Netherlands organization for scientific research (NWO) VIDI grant (dossier 639.042.730). MGH, GK and AR acknowledge support from ERC Advanced Grant 320596 {\textquoteleft}Emergence{\textquoteright}. AC and MH acknowledge support from the U.K. Science and Technology Facilities Council (grant numbers ST/N000927/1 and ST/S000623/1). While working on this paper, we learned about very similar work in preparation by Mukherjee et al. [40]. Although our simulation approach differs from theirs, we obtain similar conclusions. We have included comparison to their work in several places throughout this paper. Funding Information: AR would like to thank the Kavli Institute for Cosmology Cambridge (KICC) for hospitality during the early phases of this project. The authors would like to thank Marcelo Alvarez, Nicholas Battaglia, Tirthankar Roy Choudhury, Cora Dvorkin, Rishi Khatri, Ran-jan Modak, David Spergel, and Matteo Viel for useful discussions. The results presented in the paper relied on the Cambridge Service for Data Driven Discovery (CSD3) operated by the University of Cambridge (www.csd3.cam.ac.uk), provided by Dell EMC and Intel using Tier-2 funding from the Engineering and Physical Sciences Research Council (capital grant EP/P020259/1), and DiRAC funding from the Science and Technology Facilities Council (www.dirac.ac.uk). This work further used the COSMA Data Centric system operated Durham University on behalf of the STFC DiRAC HPC Facility. This equipment was funded by a BIS National E-infrastructure capital grant ST/K00042X/1, DiRAC Operations grant ST/K003267/1 and Durham University. DiRAC is part of the National E-Infrastructure. This work is partially supported by PRIN MIUR 2015 grant {\textquoteleft}Cosmology and Fundamental Physics: illuminating the Dark Universe with Euclid{\textquoteright}, PRIN INAF 2014 grant {\textquoteleft}Probing the AGN/galaxy co-evolution through ultra-deep and ultra-high-resolution radio surveys{\textquoteright}, the MIUR grant {\textquoteleft}Finanziamento annuale individuale attivita base di ricerca{\textquoteright} and the RADIO-FOREGROUNDS grant (COMPET-05-2015, agreement number 687312) of the European Union Horizon 2020 research and innovation program. PDM acknowledges support from a Kavli Institute Senior Fellowship at the University of Cambridge and the Netherlands organization for scientific research (NWO) VIDI grant (dossier 639.042.730). MGH, GK and AR acknowledge support from ERC Advanced Grant 320596 {\textquoteleft}Emergence{\textquoteright}. AC and MH acknowledge support from the U.K. Science and Technology Facilities Council (grant numbers ST/N000927/1 and ST/S000623/1). While working on this paper, we learned about very similar work in preparation by Mukherjee et al. [40]. Although our simulation approach differs from theirs, we obtain similar conclusions. We have included comparison to their work in several places throughout this paper. Publisher Copyright: {\textcopyright} 2021 IOP Publishing Ltd and Sissa Medialab.",
year = "2021",
month = jan,
doi = "10.1088/1475-7516/2021/01/003",
language = "English",
volume = "2021",
journal = "Journal of Cosmology and Astroparticle Physics",
issn = "1475-7516",
publisher = "IOP PUBLISHING LTD",
number = "1",
}