Duncan Watts

• Núñez, Carolina; Appel, John W.; Datta, Rahul; Bennett, Charles L.; Brewer, Michael K. & Bruno, Sarah Marie [Show all 25 contributors for this article] (2025). High-efficiency and Low-noise Detectors for the Upgraded CLASS 90 GHz Focal Plane. Astrophysical Journal Supplement Series. ISSN 0067-0049. 278(2). doi: 10.3847/1538-4365/adc602. Full text in Research Archive Show summary

  We present the in-lab and on-sky performance for the upgraded 90 GHz focal plane of the Cosmology Large Angular Scale Surveyor, which had four of its seven detector wafers updated during the austral winter of 2022. The update aimed to improve the transition-edge-sensor (TES) stability and bias range and to realize the high optical efficiency of the sensor design. Modifications included revised circuit terminations, electrical contact between the TES superconductor and the normal metal providing the bulk of the bolometer heat capacity, and additional filtering on the TES bias lines. The upgrade was successful: 94% of detectors are stable down to 15% of the normal resistance, providing a wide overlapping range of bias voltages for all TESs on a wafer. The median telescope efficiency improved from 0.4 2 − 0.22 + 0.15 to 0.6 0 − 0.32 + 0.10 (68% quantiles). For the four upgraded wafers alone, median telescope efficiency increased to 0.6 5 − 0.06 + 0.06 . Given our efficiency estimate for the receiver optics, this telescope efficiency implies a detector efficiency exceeding 0.90. The overall noise-equivalent temperature of the 90 GHz focal plane improved from 19 μ K s to 9.7 μ K s .

• 李, Yunyang 云炀 Li; Eimer, Joseph R.; Appel, John W.; Bennett, Charles L.; Brewer, Michael K. & Bruno, Sarah Marie [Show all 37 contributors for this article] (2025). A Measurement of the Largest-scale CMB E-mode Polarization with CLASS. The Astrophysical Journal (ApJ). ISSN 0004-637X. 986(2). doi: 10.3847/1538-4357/adc723. Full text in Research Archive Show summary

  We present measurements of large-scale cosmic microwave background E -mode polarization from the Cosmology Large Angular Scale Surveyor 90 GHz data. Using 115 det-yr of observations collected through 2024 with a variable-delay polarization modulator, we achieved a polarization sensitivity of 82 μ K arcmin , comparable to Planck at similar frequencies (100 and 143 GHz ). The analysis demonstrates effective mitigation of systematic errors and addresses challenges to large-angular-scale power recovery posed by time-domain filtering in maximum-likelihood map-making. A novel implementation of the pixel-space transfer matrix is introduced, which enables efficient filtering simulations and bias correction in the power spectrum using the quadratic cross-spectrum estimator. Overall, we achieved an unbiased time-domain filtering correction to recover the largest angular scale polarization, with the only power deficit, arising from map-making nonlinearity, being characterized as <3%. Through cross-correlation with Planck, we detected the cosmic reionization at 99.4% significance and measured the reionization optical depth τ = 0.05 3 − 0.019 + 0.018 , marking the first ground-based attempt at such a measurement. At intermediate angular scales ( ℓ  > 30), our results, both independently and in cross-correlation with Planck, remain fully consistent with Planck’s measurements.

• Aurvik, Ragnhild; Galloway, Mathew; Gjerløw, Eirik; Fuskeland, Unni; Basyrov, Artem & Bortolami, M. [Show all 110 contributors for this article] (2025). On the computational feasibility of Bayesian end-to-end analysis of LiteBIRD simulations within Cosmoglobe. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(11). doi: 10.1088/1475-7516/2025/11/041. Full text in Research Archive Show summary

  We assess the computational feasibility of end-to-end Bayesian analysis of the JAXA-led LiteBIRD experiment by analysing simulated time ordered data (TOD) for a subset of detectors through the Cosmoglobe and Commander3 framework. The data volume for the simulated TOD is 1.55 TB, or 470 GB after Huffman compression. From this we estimate a total data volume of 238 TB for the full three year mission, or 70 TB after Huffman compression. We further estimate the running time for one Gibbs sample, from TOD to cosmological parameters, to be approximately 3000 CPU hours. The current simulations are based on an ideal instrument model, only including correlated 1/ f noise. Future work will consider realistic systematics with full end-to-end error propagation. We conclude that these requirements are well within capabilities of future high-performance computing systems.

• Hoz, E. de la; Diego-Palazuelos, P.; Errard, J.; Gruppuso, A.; Jost, B. & Sullivan, Raelyn [Show all 115 contributors for this article] (2025). LiteBIRD science goals and forecasts: constraining isotropic cosmic birefringence. Journal of Cosmology and Astroparticle Physics (JCAP). 2025(7). doi: 10.1088/1475-7516/2025/07/083. Full text in Research Archive Show summary

  Cosmic birefringence (CB) is the rotation of the photons' linear polarisation plane during propagation. Such an effect is a tracer of parity-violating extensions of standard electromagnetism and would probe the existence of a new cosmological field acting as dark matter or dark energy. It has become customary to employ cosmic microwave background (CMB) polarised data to probe such a phenomenon. Recent analyses on Planck and WMAP data provide a hint of detection of the isotropic CB angle with an amplitude of around 0.3° at the level of 2.4 to 3.6σ. In this work, we explore the LiteBIRD capabilities in constraining such an effect, accounting for the impact of the more relevant systematic effects, namely foreground emission and instrumental polarisation angles. We build five semi-independent pipelines and test these against four different simulation sets with increasing complexity in terms of non-idealities. All the pipelines are shown to be robust and capable of returning the expected values of the CB angle within statistical fluctuations for all the cases considered. We find that the uncertainties in the CB estimates increase with more complex simulations. However, the trend is less pronounced for pipelines that account for the instrumental polarisation angles. For the most complex case analysed, we find that LiteBIRD will be able to detect a CB angle of 0.3° with a statistical significance ranging from 5 to 13σ, depending on the pipeline employed, where the latter uncertainty corresponds to a total error budget of the order of 0.02°.

• Shi, Rui; Appel, John W.; Bennett, Charles L.; Bustos, Ricardo; Chuss, David T. & Dahal, Sumit [Show all 21 contributors for this article] (2024). Sensitivity-improved Polarization Maps at 40 GHz with CLASS and WMAP Data. The Astrophysical Journal (ApJ). ISSN 0004-637X. 971(1). doi: 10.3847/1538-4357/ad5313. Full text in Research Archive
• Datta, Rahul; Brewer, Michael K.; Couto, Jullianna Denes; Eimer, Joseph; Li, Yunyang & Xu, Zhilei [Show all 34 contributors for this article] (2024). Cosmology Large Angular Scale Surveyor (CLASS): 90 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance. Astrophysical Journal Supplement Series. ISSN 0067-0049. 273(2). doi: 10.3847/1538-4365/ad50a0. Full text in Research Archive
• Eimer, Joseph R.; Li, Yunyang; Brewer, Michael K.; Shi, Rui; Ali, Aamir & Appel, John W. [Show all 34 contributors for this article] (2024). CLASS Angular Power Spectra and Map-component Analysis for 40 GHz Observations through 2022. The Astrophysical Journal (ApJ). ISSN 0004-637X. 963(2). doi: 10.3847/1538-4357/ad1abf. Full text in Research Archive
• Watts, Duncan; Fuskeland, Unni; Aurvik, Ragnhild; Basyrov, Artem; Bianchi, L.A. & Brilenkov, Maksym [Show all 21 contributors for this article] (2024). COSMOGLOBE DR1 results: III. First full-sky model of polarized synchrotron emission from all WMAP and Planck LFI data. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 686. doi: 10.1051/0004-6361/202348330. Full text in Research Archive Show summary

  We present the first model of full-sky polarized synchrotron emission that is derived from all WMAP and Planck LFI frequency maps. The basis of this analysis is the set of end-to-end reprocessed COSMOGLOBE Data Release 1 (DR1) sky maps presented in a companion paper, which have significantly lower instrumental systematics than the legacy products from each experiment. We find that the resulting polarized synchrotron amplitude map has an average noise rms per 2° full width at half maximum (FWHM) beam of 3.2 μK at 30 GHz. This is 30% lower than the recently released BEYONDPLANCK model that included only LFI+WMAP Ka–V data, and 29% lower than the WMAP K-band map alone. The mean B-to-E power spectrum ratio is 0.39 ± 0.02, with amplitudes consistent with those measured previously by Planck and QUIJOTE. Assuming a power law model for the synchrotron spectral energy distribution and using the T–T plot method, we find a full-sky inverse noise-variance-weighted mean of the synchrotron polarized spectral index of βs = −3.07 ± 0.07 from the COSMOGLOBE DR1 K band and 30 GHz, in good agreement with previous estimates. In summary, the novel COSMOGLOBE DR1 synchrotron model is both more sensitive and systematically cleaner than similar previous models, and it has a more complete error description that is defined by a set of Monte Carlo posterior samples. We believe that these products are preferable over previous Planck and WMAP products for all synchrotron-related scientific applications, including simulations, forecasting, and component separation.

• Basyrov, Artem; Stutzer, Nils-Ole; Lunde, Jonas Gahr Sturtzel; Eriksen, Hans Kristian Kamfjord; Gjerløw, Eirik & Watts, Duncan [Show all 7 contributors for this article] (2024). Optimal bolometer transfer function deconvolution for CMB experiments through maximum likelihood mapmaking. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 688. doi: 10.1051/0004-6361/202450712. Full text in Research Archive Show summary

  We revisit the impact of finite time responses of bolometric detectors used for deep observations of the cosmic microwave background (CMB). Until now, bolometer transfer functions have been accounted for through a two-step procedure by first deconvolving an estimate of their Fourier-space representation from the raw time-ordered data (TOD), and then averaging the deconvolved TOD into pixelized maps. However, for many experiments, including the Planck High Frequency Instrument (HFI), it is necessary to apply an additional low-pass filter to avoid an excessive noise boost, which leads to an asymmetric effective beam. In this paper we demonstrate that this effect can be avoided if the transfer function deconvolution and pixelization operations are performed simultaneously through integrated maximum likelihood mapmaking. The resulting algorithm is structurally identical to the artDeco algorithm for beam deconvolution. We illustrate the relevance of this method with simulated Planck HFI 143 GHz data, and find that the resulting effective beam is both more symmetric than with the two-step procedure, resulting in a sky-averaged ellipticity that is 64% lower, and an effective beam full-width-at-half-maximum (FWHM) that is 2.3% smaller. Similar improvements are expected for any other bolometer-based CMB experiments with long time constants.

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• San, Metin; Wehus, Ingunn Kathrine; Eriksen, Hans Kristian Kamfjord; Watts, Duncan; Doré, Olivier & Elgarøy, Øystein (2024). Modelling the infrared sky through global end-to-end analysis. Faculty of Mathematics and Natural Sciences. Full text in Research Archive

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