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The standard Λ Cold Dark Matter cosmological model provides a wonderful fit to current cosmological data, but a few statistically significant tensions and anomalies were found in the latest data analyses. While these anomalies could be due to the presence of systematic errors in the experiments, they could also indicate the need for new physics beyond the standard model. In this Letter of Interest we focus on the tension between Planck data and weak lensing measurements and redshift surveys, in the value of the matter energy density Ω m and the amplitude σ 8 (or the growth rate f σ 8 ) of cosmic structure. We list a few promising models for solving this tension, and discuss the importance of trying to fit multiple cosmological datasets with complete physical models, rather than fitting individual datasets with a few handpicked theoretical parameters.

We describe the design and in–flight performance of the cryostat and the self–contained\ud\udHe refrigerator for the OLIMPO balloon–borne experiment, a spectrophotometer to measure the Sunyaev–Zel’dovich effect in clusters of galaxies.\ud\udThe\udHe refrigerator provides the 0.3 K operation temperature for the four arrays of kinetic inductance detectors working in 4 bands centered at 150, 250, 350 and 460 GHz. The cryostat provides the 1.65 K base temperature for the\ud\udHe refrigerator, and cools down the reimaging optics and the filters chain at about 2 K.\ud\udThe integrated system was designed for a hold time of about 15 days, to achieve the sensitivity required by the planned OLIMPO observations, and successfully operated during the first long–duration stratospheric flight of OLIMPO in July 2018.\ud\udThe cryostat features two tanks, one for liquid nitrogen and the other one for liquid helium. The long hold time has been achieved by means of custom stiff G10 fiberglass tubes support, which ensures low thermal conductivity and remarkable structural stiffness; multi–layer superinsulation, and a vapour cooled shield, all reducing the heat load on the liquid helium tank.\ud\udThe system was tested in the lab, with more than 15 days of unmanned operations, and then in the long duration balloon flight in the stratosphere. In both cases, the detector temperature was below 300 mK, with thermal stability better than\ud\ud0.5 mK.\ud\udThe system also operated successfully in the long duration stratospheric balloon flight.

The Boomerang experiment completed its final long duration balloon (LDB) flight over Antarctica in January 2003. The focal plane was upgraded to accommodate four sets of 145 GHz polarization sensitive bolometers (PSBs), identical to those to be flown on the Planck HFI instrument. Approximately, 195 hours of science observations were obtained during this flight, including 75 hours distributed over 1.84% of the sky and an additional 120 hours concentrated on a region covering 0.22% of the sky. We derive the angular power spectra of the cosmic microwave background (cmb) temperature and polarization anisotropies from these data. The temperature anisotropies are detected with high signal to noise on angular scales ranging from several degrees to ∼10 arcminutes. The curl-free (EE) component is detected at ∼4.8σ, and a two-sigma upper limit on the curl (BB) component of 8.6 μK2 is obtained on scales corresponding to ∼0.5°. Both the temperature and polarization anisotropies are found to be consistent with a concordance ΛCDM cosmology that is seeded by adiabatic density perturbations. In addition to the cmb observations, Boomerang03 surveyed a ∼300 square degree region centered on the Galactic plane. These observations represent the first light for polarization sensitive bolometers, which are currently operational in two South-Pole based polarimeters, as well as Planck HFI, at frequencies ranging from 100 to 350 GHz (3 mm to 850 μm).

We describe a 4 He cryostat suitable for cooling a large (about 50 l in volume) multiband bolometric photometer for mm-waves. The cryostat features two large optical windows and a hold time longer than 2 weeks. The long hold time has been obtained using a 20 K vapour cooled shield for the liquid helium tank and superinsulation for the nitrogen tank. The tanks are supported by kevlar cords. The cryostat has been optimized for operation on long duration stratospheric balloon flights, and has been tested successfully at ground level and on two short balloon flights.

The Cosmic Microwave Background (CMB) represents a window on the early universe, and allows observers to test cosmological models and fundamental physics, including neutrino physics. Ground-based, balloon-borne and satellite experiments in the last decade have provided sensitive measurements of the CMB, precision estimates of the cosmological parameters, and strong constraints on neutrino properties. The forthcoming Planck mission of the European Space Agency will provide definitive measurements of the CMB and will allow a clean, unambiguous separation of foreground and background microwave emission. Here we summarize the most recent results and discuss new perspectives in this field and their impact on cosmology and fundamental physics.