Objectives of the proposal
Investigating the physics of the early Universe is the great goal of cosmology and fundamental physics. The CMB is certainly the most powerful and natural tool to constrain models of particle physics at energies which will be never reached by laboratory experiments and to trace new physics beyond the standard model. In particular, the detection of tensor perturbations of the space-time metric, which lead to a primordial gravitational wave background – PGWB, is a smoking gun for the inflationary theory of the early universe. The PGWB imprints a unique pattern (the so called B-modes) in the polarization of CMB photons. Therefore, the primary scientific exploitation of CMB B-mode data aims to a definitive probe of the inflation paradigm and to an estimate of the energy scale at which inflation occurs. Another crucial observable to probe the physical mechanism behind inflation is primordial non-Gaussianity (PNG), in that it allows to test the interactions among quantum fields during inflation and, along with PGWB, it can also distinguish among very different mechanisms and models. Finally, it must be underlined that the observation of the microwave sky is important also for astrophysical and fundamental physics problems that are of interest per se and that are on the frontier of current research: Galactic foregrounds, physics of galaxy clusters, gravitational lensing as a probe of the dark matter, astrophysics of point sources, neutrino physics and, not to be forgotten, the issue of the CMB spectral distortions. All these aspects are strongly interconnected and it is difficult to have a breakthrough without considering them all.
The Planck mission (with Italian leadership in its LFI instrument) has by all practical means exhausted the information content of the cosmic microwave background (CMB) temperature anisotropies. The CMB temperature anisotropy dataset from Planck is publicly available, and its ultimate, legacy release is expected by 2016. Planck has established a major breakthrough in the comprehension of the current concordance model of cosmology, the so-called LCDM model. At the same time, Planck’s exploitation of the weak CMB polarization modes has opened a new channel and a new era in the observations of the polarized microwave sky that needs to be continued with future experiments. The Italian led LSPE effort, financed by ASI and INFN is already on this track. In the background, there are CORE (a proposal for a post Planck CMB satellite to be submitted within the ESA M5 Call) as well as the sub-orbital USA led S4 program.
In order to reach this ambitious goal, it is necessary to exploit in an integrated and synergic way all the different kinds of expertise that the Italian CMB community has developed over the years. We definitely need to study the scientific potential and technical feasibility of a medium-long term (5- 15 years) program to measure the CMB polarization from sub-orbital platforms, identifying different observation strategies, with and without a CORE/ESA-M5 or other missions like LiteBird/JAXA. But we also need, at the same time, to have full control of a number of foregrounds. First, the B-modes from diffuse Galactic foregrounds, in spite of the Planck results, are still far from being completely understood and under control at the sensitivity and angular resolution required to hunt for primordial CMB B-modes over all the sky. Second, gravitational lensing removal is a subject that requires to be further developed and understood if we want to measure CMB B-modes at all accessible multipoles with the required accuracy. Third, clusters of galaxies and point sources contribution in the observed dataset must be also known to high precision. Last, but not least, simulations and data analysis tools have to be developed in strong connection with all the activities mentioned above. This project will start from coordinating at the national level the OLIMPO and LSPE data analysis effort, having in mind the need to go beyond these experiments both in terms of tools and computation power.
Therefore, the purpose of this proposal, which – we want to stress it – includes all the Italian CMB community, is to define a sustainable road map for the CMB cosmology and astrophysics of the next few years that will allow this community to participate with a high profile role to the main international collaborations of future challenging orbital and sub-orbital experiments. There is also another aspect that we would like to stress as a strategic goal of our community: the formation of a new generation of cosmologists and astrophysicists involved in instrument design and realization, CMB observations, theory and simulation/data analysis activity. These young researchers will contribute to reinforce the leading international role that the CMB Italian community has played up to now.
This three-year project is coordinated by Nicola Vittorio (Università di Tor Vergata) and it is structured in 11 nodes (7 Universities, 2 INAF Institutions, 2 INFN Sections).
Each node has the responsibility of coordinating the activity, monitoring the implementation and delivering of products related to the specific expertise built in the last decades, which will be the result of a genuine, synergic and interactive effort done at the national level by all the interested researchers. The final outcome of this project will be the definition of an Italian road map in the field of CMB research for the next decade.