With this proposal, we request support for activity in the field of observational cosmology at millimeter band, with particular focus on the observation of the Cosmic Microwave Background radiation (CMB). The group has a historical leadership in this field, which is becoming more and more complex, with an extremely high level of quality of the results reached at international level.
We thus need support to maintain the high level of contribution to the filed at international level, and to be able to make further progress in the design, and prototyping of instrumentation.
We are currently collaborating to projects: LPSE (with leading role), QUBIC (with co-leading role), OLIMPO (with leading role). We are also going to have a co-leading role, at European level, of the next approves space mission LiteBIRD, a JAXA granted mission for high accuracy, polarization measurements¿ of the CMB and its foregrounds.
All these activities, beside the needed support from Space Agency, or research institute for Hardware production, require support for travel, instrument optimization, development of new instruments, and participation to international collaborations.
WP1: LSPE. The modulation of the faint polarized CMB is one of the key elements of the experiment. It is obtained by means of a cryogenic rotating Half WavePlate (HWP). This configuration has important advantages:
- It moves the signal from the frequency range induced by sky scan (fractions of Hz) to 4 times the rotation frequency (~10 Hz) so that the effects of 1/f noise from the atmosphere and the instrument are mitigated;
- There is more freedom in optimizing the sky coverage (obtained by spinning the payload in azimuth and changing the elevation).
In LSPE the HWP is the first optical element. In this configuration, the polarization properties of the subsequent telescope and detectors are almost irrelevant. But the HWP has a diameter of 50 cm to cover the full beam of the experiment [see Pisano et al. arXiv:1610.00582] and needs to be cooled at cryogenic temperatures to avoid introducing important offsets. We have designed a cryogenic rotator based on a large superconducting bearing to achieve continuous rotation at a few K with minimal dissipation and high stability. In this WP we¿ll optimize the rotation frequency of the HWP and the sky scan by means of
- Accurate modeling of HWP-induced systematics;
- Development of a detailed instrument simulator accounting for these systematic effects;
- End-to-end simulations of the LSPE survey, for different rotation frequencies, scan speeds, elevation steps.
WP2: QUBIC. The QUBIC experiment is in demonstration phase and will be deployed to the observation site (Alto Chorrillo, Argentina) in 2020. Our group has produced the main cryogenic system, and the polarization modulator. Our presence will be needed during the instrument installation and commissioning at the high-altitude site. In addition, we plan to develop a parallel data analysis pipeline, modifying the LSPE pipeline to account for the peculiar beam of the interferometer and its frequency dependence.
WP3: OLIMPO and Observations of Clusters with Sunyaev-Zeldovich effect. OLIMPO was flown in Summer 2018 from Svalbard (NO). First results are published in Masi et al. (JCAP 2019 accepted - arXiv:1902.08993). The group is now analyzing the data of the mission and refurbishing the payload for the next flight. Observations of the SZE will also be carried out using ground-based observatories with application to call for observations. As of today, the group has got approved 66 hours of observations at the Green Bank Radio Telescope, to measure the presence of hot plasma in the intergalactic filament between clusters Abell-401 and Abell-399; this activity requires financial support for travel to the observing site.
WP4: KINETIC INDUCTANCE DETECTORS. We propose to study detector arrays for the W band. These require a technological step, which is the use of a binary layer superconductor, and the optimization of a large-size focal plane. Here we ask support for the simulation activities and for the production and test of samples and focal plane components.
WP5: PREPARATION OF LiteBIRD.
After Planck, LiteBIRD represents the next opportunity, at international level, for a space mission devoted to CMB polarization. LiteBIRD has been selected by JAXA, and Europe aims to play a major role in the collaboration, by taking responsibility of two of the three instruments on board the spacecraft. JAXA itself is counting on the contribution from ESA and European national space agencies to fulfill the mission. The group is playing a leading role in Italy and Europe, and is looking for funding for a relevant hardware contribution to the instrument. Considering the limited budget of this call, here we would like to grant the possibility to participate to international meetings, to participate to the optimization of the instrument design, to develop data analysis and science exploitation methods, in collaboration with other Italian, European, and international collaborators. This clearly requires traveling and computational costs.
WP6: FORECAST FOR FUTURE EXPERIMENTS AND IMPACT ON SCIENCE.
This WP will be dedicated to evaluating the scientific impact of current and future CMB probes. Future CMB lensing measurements could discriminate between a standard cosmological constant and ¿time-evolving dark energy. Moreover, there is the possibility that dark energy interacts with other components as cold dark matter and, again, CMB lensing can shed light on this. Even more extreme hypothesis of modifications to General Relativity could be considered. Finally, according to current bounds on neutrino masses, neutrino also changes from a relativistic to a nonrelativistic regime in an epoch after CMB recombination, even leaving characteristic imprints on CMB lensing. Understanding and solving current anomalies in the CMB lensing could, therefore, help in placing new sharp bounds on neutrino masses, testing the neutrino mass hierarchy and possibly providing the first measurement for the neutrino absolute mass scale.