Precision cosmology from early and late-time surveys.

Lead Research Organisation: Cardiff University
Department Name: School of Physics and Astronomy

Abstract

The cosmological quest is mainly fed by the curiosity to know how things started and evolved in time, which particular process led to the objects we see in the sky (e.g., galaxies and clusters of galaxies), where they come from and why they are moving away from us.

A key aspect of physics of the early Universe is the theory and the observation of the cosmic microwave background radiation (CMB) temperature fluctuations and polarisation. The use of the CMB to study the particle and energy content of the Universe as well as its evolution is a remarkable success of modern cosmology.
The CMB is the most ancient light we can observe in the Universe. It was born in the early Universe a few seconds after the Big Bang and thermalised in the primordial 'cosmic soup' where the high Universe temperature coupled light together with other particles. It then decoupled and was released when the Universe cooled down and the first light elements started to form (e.g., hydrogen and helium), leaving CMB photons free to escape. The CMB then provides us with a snapshot and unique view of the transparent Universe. It has been free to travel from the decoupling moment to today and it reaches us as a faint radiation with microwave wavelengths. The way it propagates and its statistical properties inform us about the physics of the early Universe (looking back in time from decoupling) and describes its particle/energy content and evolution (looking forward in time from decoupling). The statistics of the CMB temperature variations have now been measured with extreme precision over a broad range of scales, leading to a concordance standard model of cosmology. However, the standard cosmological model arising today relies on observational evidence for components and processes with unknown theoretical interpretation. We measure that 95% of the Universe is dominated by 'dark' components but we don't know yet what their nature is. We call 'dark matter' the component responsible for the galaxies formation and 'dark energy' the force opposing gravity and driving the Universe in an accelerating expansion, all this assuming that the laws of gravity are correct on all scales. We also need to invoke a super-luminal expansion in the first fraction of a second after the Big Bang to account for the homogeneity of the Universe on cosmic scales and its flatness. In the last ten years CMB data has become the most competitive and tantalising source of information to address these open theoretical issues.

My project relies on two kinds of observations complementing current data in the next decade: improved measurement of CMB polarisation and the measurement of galaxies statistics and distribution on the largest physical scales (e.g., galaxy clusters, voids, filaments, bubbles) over a broad cosmic epoch.
At the end of 2013 and early 2014 the new measurements of CMB polarisation from gound-based experiments have kicked off a new era in CMB physics. CMB polarisation will inform our understanding of the brief expansion phase of the early Universe (called cosmic inflation), probing high energy scales not testable in laboratories, and will map the gravitational potential field defining the geometry, evolution and content of the Universe. CMB polarisation is particularly effective for studying the masses of primordial neutrinos, still unmeasured today.
Current and future probes of the Universe large-scale structure, via galaxy surveys, will be instead effective in characterising the dark sector and testing the gravity laws on cosmic scales.
The combination of CMB and galaxy surveys will increase the fidelity of the cosmological reconstructions, reducing systematics and probing many cosmic epochs (the CMB gives us a snapshot of a ~400,000 years old Universe while galaxy surveys probe the last 10 billion years).

Publications

10 25 50

Related Projects

Project Reference Relationship Related To Start End Award Value
ST/M004856/1 31/03/2016 30/04/2017 £459,193
ST/M004856/2 Transfer ST/M004856/1 01/05/2017 31/03/2021 £369,333
 
Description ACT 
Organisation Princeton University
Country United States 
Sector Academic/University 
PI Contribution I am a science team member of the Atacama Cosmology Telescope. For this experiment I lead characterization and cosmological interpretation of cosmic microwave data.
Collaborator Contribution ACT is a ground-based telescope, located in Chile, in the Atacama desert. The Collaboration consists of many teams, including instrumentalists and data analysis and theory experts, working together on different aspects of the mission. I work at the end of the pipeline, needing access to the data.
Impact ACT is one of the leading experiments in cosmology, providing increasingly accurate data to understand the physics of the early universe. Since 2011, when I first joint the ACT Collaboration, ACT has delivered: -- new methodology to characterise small-scale temperature data in the microwave; -- first measurement of small-scale CMB polarisation; -- state-of-the-art constraints on cosmology from small-scale temperature, including limits on the neutrino number and mass and parameters characterising inflation; -- first evidence of CMB halo lensing (at 3sigma) using SDSS-BOSS galaxies; -- kSZ detections from different CMB-galaxy cross-correlations. Since the award of this fellowship I have participated to 5 ACT papers.
Start Year 2011
 
Description Planck 
Organisation European Space Agency
Country France 
Sector Public 
PI Contribution I am a Planck Collaboration Scientist, contributing to the analysis of the European Space Agency Planck satellite data. I bring my expertise on modelling and characterizing small-scale cosmic microwave data, and on combining the Planck data with observations from other experiments, leading to robust, state-of-the-art cosmological constraints.
Collaborator Contribution Planck is a space mission measuring the primordial microwave radiation. The Collaboration consists of many teams, including instrumentalists and data analysis and theory experts, working together on different aspects of the mission. I work at the end of the pipeline, needing access to the data.
Impact The Planck data have led to more than 100 publications, setting the current state of the art of cosmology from cosmic microwave background. Since 2013, with the first data release, Planck has: -- set the most stringent bounds on the cosmological parameters characterising the universe content and evolution, including bounds on the total mass of neutrino particles, constraints on the early universe thermal condition, limits on inflation scenarios, bounds on dark energy and modified gravity theories, and limits on the dark matter particle nature; -- provided an enormous amount of ancillary data, characterising the Galaxy and nearby galaxies and clusters of galaxies at different frequencies. Since the award of this Fellowship I have participated to 12 Planck papers.
Start Year 2014
 
Description Cardiff Sixth Form College 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Talk about cosmology to Sixth Form A-level students and physics teacher.
Year(s) Of Engagement Activity 2019
 
Description Cheltenham Science Festival 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Panel member at the event "The Universe: What Don't We Know" at the Cheltenham Science Festival.
Year(s) Of Engagement Activity 2017
URL https://www.cheltenhamfestivals.com/science
 
Description Cheltenham Science Festival 2018 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Panel member at the event "Beyond Einstein: The Future of Physics" at the Cheltenham Science Festival.
Year(s) Of Engagement Activity 2018
URL https://www.cheltenhamfestivals.com/science
 
Description Interviews for Nature Astronomy and New Scientist Magazine 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Interviews on CMB cosmology post-Planck and future science goals.
Year(s) Of Engagement Activity 2018,2019
 
Description Invited seminar at ECMB 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Invited seminar at the European CMB meeting in Florence and participation to the discussion of the European coordination of the CMB programme.
Year(s) Of Engagement Activity 2017
URL https://indico.in2p3.fr/event/14661/
 
Description Invited seminars and Colloquia at Stockholm, Cambridge, Royal Astronomical Society Institute of Physics Cosmology day, Tenerife, Rome 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Invited seminars and colloquia at physics and astrophysics department to present my research. For each event ~20-40 people including undergraduate and graduate students, faculty and staff members, were present.
Year(s) Of Engagement Activity 2018,2019