Topics in Cosmic Microwave Background delensing
Lead Research Organisation:
University of Cambridge
Department Name: Institute of Astronomy
Abstract
The first project we are working on consists of preparing a pipeline for "delensing" the B mode of polarization of the Cosmic Microwave Background (CMB). This means removing the contribution to this curl-like type of polarization attributed to the gravitational lensing of CMB photons as they traverse the large scale structure of the Universe. The reason this is important is that this effect dominates over and 'hides' the primordial B mode that can be attributed to gravitational waves generated during inflation, which are believed to be the 'smoking gun' of inflationary theory.
In order to estimate the B mode generated by gravitational lensing in a particular patch of the sky, one needs to have an estimate for what the projection of the matter distribution between the CMB and us looks like locally. This can be obtained either from external surveys or -if the experimental noise levels are low enough- internally from the CMB. The latter approach is what we are incorporating into our pipeline, as the next generation of CMB experiments will permit us to do this -more optimal- type of reconstruction. In particular, we are tailoring our work to the characteristics of the Simon Observatory, of which my supervisor is a member. The goal is to be able to accurately model the delensing procedure -properly accounting for the relevant biases- and establish a framework for detecting a primordial B mode in the delensed maps if its signal level allows for it.
In order to estimate the B mode generated by gravitational lensing in a particular patch of the sky, one needs to have an estimate for what the projection of the matter distribution between the CMB and us looks like locally. This can be obtained either from external surveys or -if the experimental noise levels are low enough- internally from the CMB. The latter approach is what we are incorporating into our pipeline, as the next generation of CMB experiments will permit us to do this -more optimal- type of reconstruction. In particular, we are tailoring our work to the characteristics of the Simon Observatory, of which my supervisor is a member. The goal is to be able to accurately model the delensing procedure -properly accounting for the relevant biases- and establish a framework for detecting a primordial B mode in the delensed maps if its signal level allows for it.
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| ST/R50466X/1 | 01/10/2017 | 30/09/2021 | |||
| 1951725 | Studentship | ST/R50466X/1 | 01/10/2017 | 30/09/2020 | Anton Baleato Lizancos |
| Description | Gravitational lensing of CMB photons by the matter distribution of the Universe can be both a blessing and nuisance. It's a blessing because of the way it can be harnessed to map the structures responsible for the deflections, and from this, constrain any physics affecting the growth of cosmic structure, such as the sum of the neutrino masses or dark matter. But lensing is also a nuisance because it generates B-mode polarization which obscures the highly-sought-after primordial signal associated with gravitational waves generated during cosmic inflation, our most accessible portal to the physics of the very early Universe. This award has investigated several key systematic effects that need to be controlled in order to harness the full potential of the Simons Observatory (SO), CMB-S4, and other upcoming experiments to make progress in these exciting areas. On the one hand, we have developed tools to calculate the impact of spurious emission from galaxies and clusters on our efforts to glean insights about fundamental physics affecting the late-time evolution of the Universe, such as the sum of the neutrino masses. The tools we are developing will be a powerful complement to existing tools striving to minimise this contamination. On the other hand, we have studied in detail the ways in which the lensing contamination to CMB B-modes can be removed - what is known as delensing - and clarified key questions about the performance of different delensing methods. We have also carried out preparatory work to delens SO data, and highlighted biases to watch out for (and how to mitigate them) when the matter proxy used for delensing is either the cosmic infrared background or a lensing reconstruction derived from the CMB itself. |
| Exploitation Route | The insights we have developed will need to be taken into account in order to maximise the ability of upcoming CMB observatories such as the South Pole Observatoy, the Simons Observatory, or CMB-S4, to learn about fundamental physics. |
| Sectors | Other |
| URL | https://www.ast.cam.ac.uk/people/anton.baleato |
| Description | Our work is beginning to have an impact (visible through citations) on the cosmology community. It informs the community's central effort to infer how our Universe began, a goal that might be within the reach of experiments coming online within the next decade. |
| First Year Of Impact | 2021 |
| Sector | Other |
| Impact Types | Cultural |
| Description | Rouse Ball Research Bursary -- Trinity College, Cambridge |
| Amount | £600 (GBP) |
| Organisation | University of Cambridge |
| Sector | Academic/University |
| Country | United Kingdom |
| Start | 10/2017 |
| End | 03/2021 |
| Description | Member of the Simons Observatory |
| Organisation | Simons Observatory |
| Country | Chile |
| Sector | Academic/University |
| PI Contribution | I am a member of the Analysis Working group of the Simons Observatory collaboration, which focuses on how to extract as much theoretical insight as possible from the data that this experiment will be collecting. In particular, I have joined efforts to "clean" observations of the cosmic microwave background from distortions arising from gravitational lensing. Along with my collaborators, we have designed a pipeline that we expect to apply to this end, and we have validated it against simulations. Futhermore, we have inspected possible biases that we might expect once we move to a more realistic implementation where real-world effects are included, thinking always about how to best mitigate them. |
| Collaborator Contribution | A project of this nature is the product of the dedicated labour of several hundred scientists. Hence, my own work is but a drop in the bucket of all contributions, which are too numerous and diverse to describe in detail. In general terms, many groups within the collaboration focus on the hardware side, others on the conversion of raw data into maps, and yet others, among which I am included, on the extraction of cosmological information from the data. |
| Impact | The experiment is yet to start collecting data. For now, here are summaries of the expected scientific outcomes: https://arxiv.org/abs/1808.07445 https://arxiv.org/pdf/1907.08284.pdf |
| Start Year | 2018 |
| Description | Participation in a Data Study Group at the Alan Turing Institute in collaboration with the WWF |
| Organisation | Alan Turing Institute |
| Country | United Kingdom |
| Sector | Academic/University |
| PI Contribution | Participated in a week-long data study group tackling a challenge presented by the World Wildlife Fund. The goal -- which we ultimately we able to satisfy -- was to put together an automated, real-time framework for the detection of news articles published around the world covering threats to biodiversity, and the extraction of information on the relevant stakeholders. Personally, I focused on the automated, unsupervised identification of topics covered in the news articles and their subsequent use as features when discerning between relevant and irrelevant articles. In addition to this, I also explored implementations of active learning, which speeds up learning by asking a human to label certain, critical news articles. This optimises the overall performance of the classifier for a fixed amount of human input. |
| Collaborator Contribution | I worked as part of a team of 15 or so data scientists. The two PI's, responsible for convening the groups and organising the logistics, were affiliated with the Alan Turing Institute. Two other people were professionals at the WWF and brought us the data and conservation knowledge that we based our work on. The remaining dozen or so participants were data scientists from a range of branches of industry and academia. |
| Impact | The infrastructure we built will be used by the World Wildlife Fund. A paper is currently in preparation. |
| Start Year | 2019 |
| Description | (remote) Talk as part of the CMB Stage-IV planning meeting in San Diego |
| Form Of Engagement Activity | A formal working group, expert panel or dialogue |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Presented my research -- upon being invited by the organisers to do so -- to a large international cohort of scientists planning the next-generation experiment to study the cosmic microwave background |
| Year(s) Of Engagement Activity | 2019 |
| URL | https://cmb-s4.org/wiki/images/AntonBL_S4meeting.pdf |
| Description | Contributed talk at the 30th Texas Symposium on relativistic Astrophysics |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | I gave a contributed talk at this major international meeting, as part of the Cosmic Microwave Background parallel session. This opportunity then led to fruitful discussions with scientists who had been in the audience. |
| Year(s) Of Engagement Activity | 2020 |
| URL | https://texas2019.org/cmb/ |
| Description | Dissertation talk at 237th meeting of the American Astronomical Society |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Dissertation talk at the Winter Meeting of the AAS, as part of the CMB session. |
| Year(s) Of Engagement Activity | 2021 |
| URL | https://ui.adsabs.harvard.edu/abs/2021AAS...23721406B/abstract |
| Description | Flash talk and poster display at the "CosmoGold IAP 2019 The golden age of cosmology from Planck to Euclid" conference in Paris |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | I displayed a poster and gave a flash talk on my research at this major international conference organised to reflect upon the path that Cosmology ought to follow as it enters a new era of precision measurements (and perhaps growing tensions) |
| Year(s) Of Engagement Activity | 2019 |
| URL | http://www.iap.fr/vie_scientifique/colloques/Colloque_IAP/2019/ |
| Description | Flash talk and poster display at the Kavli Institute for Cosmology Cambridge 10th anniversary symposium |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | I presented a poster on my research, and advertised it briefly on stage, during this major internal gathering which gathered in Cambridge many of the world's leading cosmologists. |
| Year(s) Of Engagement Activity | 2020 |
| URL | https://www.kicc.cam.ac.uk/files/KICC10_booklet.pdf |
| Description | Invited RPM colloquium, Lawrence Berkeley National Laboratory |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Invited to give the RPM colloquium at Lawrence Berkeley National Laboratory, as part of the selection process for a Chamberlain fellowship. Talk entitled: CMB lensing & delensing for fundamental physics: the good, the bad & the systematics |
| Year(s) Of Engagement Activity | 2021 |
| Description | Invited talk at CMB lensing workshop, University of Sussex |
| Form Of Engagement Activity | A formal working group, expert panel or dialogue |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Invited seminar at expert workshop on CMB lensing at the University of Sussex |
| Year(s) Of Engagement Activity | 2020 |
| Description | Outreach talk for Cambridge University Astronomical Society |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | Local |
| Primary Audience | Undergraduate students |
| Results and Impact | Remote talk as part of the Cambridge Astronomical Society seminar series |
| Year(s) Of Engagement Activity | 2021 |
| Description | Poster at The Royal Astronomical Society's Early Career Poster Exhibition |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Displayed an online poster at the Royal Astronomical Society's Early Career Poster Exhibition |
| Year(s) Of Engagement Activity | 2020 |
| URL | https://ras.ac.uk/sites/default/files/posters/ras_poster_antonbaleatolizancos%20-%20Anton%20Baleato%... |
| Description | Public talk as part of the Institute of Astronomy's public talk series |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | Regional |
| Primary Audience | Public/other audiences |
| Results and Impact | I gave a talk entitled "Gravitational lensing: a window into the dark universe" as part of my institute's public talk series. |
| Year(s) Of Engagement Activity | 2020 |
| URL | https://www.public.ast.cam.ac.uk/gravitational-lensing-window-invisible-universe |
| Description | Public talk as part of the Institute of Astronomy's public talk series |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Public/other audiences |
| Results and Impact | I gave a talk entitled "Telescopes as Time Machines" as part of my institute's public talk series. Since the talk took place during a half-term, the audience was mostly young children, which is why I chose to focus on the fundamentals of cosmology. The talk was also live-streamed to Australia. |
| Year(s) Of Engagement Activity | 2019 |
| URL | https://www.public.ast.cam.ac.uk/telescopes-time-machines |
| Description | Public talk at the Spanish School in London, section of Galician teaching |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | Local |
| Primary Audience | Schools |
| Results and Impact | I visited the children studying Galician (a minoritised language spoken in the north of Spain) and gave an outreach talk about cosmology. We then had a nice Q&A session, some of which was filmed and uploaded to their youtube channel. |
| Year(s) Of Engagement Activity | 2017 |
| URL | https://www.youtube.com/watch?v=VvX6odHhKDk |
| Description | Public talk at the United World College of the Atlantic |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Schools |
| Results and Impact | I gave a talk in front of 60 pupils at an international school attended by pupils from dozens of different countries and a wide range of socioeconomic origins on the topic of cosmology and, more generally, careers in academia. Afterwards, we had a round-table discussion on topics of their interest, which ranged from theoretical physics to careers prospects. Several of them have followed up over email and showed great interest in science. |
| Year(s) Of Engagement Activity | 2019 |
| Description | Staff - Insitute of Astronomy Open Day |
| Form Of Engagement Activity | Participation in an open day or visit at my research institution |
| Part Of Official Scheme? | No |
| Geographic Reach | Local |
| Primary Audience | Public/other audiences |
| Results and Impact | I participated in my department's open day, showcasing a demonstration of gravitational lensing based on a computer program which allowed the user to play a game and lens a photograph of their face. |
| Year(s) Of Engagement Activity | 2018 |
| Description | Student talk at the "Cambridge Workshop on the non-Gaussian Universe" |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | I gave a student talk on my research at this workshop which brought many world-leading scientists to Cambridge |
| Year(s) Of Engagement Activity | 2019 |
| URL | http://www.ctc.cam.ac.uk/activities/ng/ |
| Description | Talk - UC Berkeley & Lawrence Berkeley National Laboratory |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Invited INPA seminar entitled: Understanding biases to CMB lensing and delensing on the road to precision science |
| Year(s) Of Engagement Activity | 2020 |
| Description | Talk as part of the Institute of Astronomy Wednesday seminar series |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | Local |
| Primary Audience | Professional Practitioners |
| Results and Impact | I gave a 25-minute talk as part of the Wednesday seminar series in my department. In the audience were academics of all levels of seniority. |
| Year(s) Of Engagement Activity | 2019 |
| Description | Talk at Harvard University |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Invited talk as part of the Cosmology journal club / seminar |
| Year(s) Of Engagement Activity | 2020 |
| Description | Talk at Insitute for Advanced Studies and Princeton University |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Invited talk as part of the cosmology journal club. Talk entitled: Understanding biases to CMB lensing and delensing on the road to precision science |
| Year(s) Of Engagement Activity | 2020 |
| Description | Talk at Institut d'Astrophysique de Paris |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Invited talk as part of the Cosmology seminar at IAP. Talk entitled: Understanding biases to CMB lensing and delensing on the road to precision science |
| Year(s) Of Engagement Activity | 2020 |
| Description | Talk at Oxford University cosmology journal club |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Professional Practitioners |
| Results and Impact | Invited talk at Oxford University cosmology journal club entitled: Understanding biases to CMB lensing and delensing on the road to precision science. |
| Year(s) Of Engagement Activity | 2020 |
| Description | Talk at Stanford University |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Invited talk as part of the CMB group meeting |
| Year(s) Of Engagement Activity | 2020 |
| Description | Talk at UCL |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Professional Practitioners |
| Results and Impact | Invited talk at UCL cosmology and extragalactic astrophysics seminar entitled: Understanding biases to CMB lensing and delensing on the road to precision science. |
| Year(s) Of Engagement Activity | 2020 |
| Description | Talk at University of Barcelona cosmology group meeting |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Invited talk at University of Barcelona cosmology group meeting entitled: Understanding biases to CMB lensing and delensing on the road to precision science. |
| Year(s) Of Engagement Activity | 2020 |
| Description | Talk at University of Geneva |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Invited talk at the University of Geneva entitled: Understanding biases to CMB lensing and delensing on the road to precision science |
| Year(s) Of Engagement Activity | 2020 |
| Description | Talk in Cambridge-LMU workshop on Large-scale structure cosmology |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Talk about recent paper: Limitations of CMB B-mode template delensing |
| Year(s) Of Engagement Activity | 2021 |
| Description | Talk in joint Center for Computational Astrophysics / NYU cosmology lunch |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Talk about recent paper: Limitations of CMB B-mode template delensing |
| Year(s) Of Engagement Activity | 2021 |
| Description | Virtual Reality visualisations of CMB science -- Website presented during department Open Day |
| Form Of Engagement Activity | Engagement focused website, blog or social media channel |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Public/other audiences |
| Results and Impact | I designed a Virtual Reality (VR) framework to visualise images related to cosmology. Though best enjoyed with a pair of VR goggles, a visitor to the website can just as well scroll around the images. I presented this tool at my department's Open Day, a yearly event drawing thousands of people. |
| Year(s) Of Engagement Activity | 2020 |
| URL | https://people.ast.cam.ac.uk/~ab2368/ |