The past twenty years have witnessed a number of breakthroughs in Astrophysics and Cosmology, that were awarded Nobel prizes: in 2019 “for theoretical discoveries in physical cosmology” and “for the discovery of an exoplanet orbiting a solar-type star”; in 2017 “for decisive contributions to the LIGO detector and the observation of gravitational waves”; in 2011 “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae”. How could we not mention the other two related breakthroughs in physics, also awarded with Nobel prizes: in 2015 “for the discovery of neutrino oscillations, which shows that neutrinos have mass”; in 2013 “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider”.
These physics triumphs serve to highlight our awareness that a Varenna School in “Gravitation and Cosmology” should provide the students with a solid and broad knowledge of the fundamentals of astrophysics and cosmology, without losing sight of the basics of the fundamental interactions in Physics. Thus, the aim of the School, held in the beautiful location of Villa Monastero from the 3rd to 12th of July 2017, was to expose students to state-of-the-art research in the field of Gravitational Waves and Cosmology, from both theoretical and experimental points of view. The choice of the subjects seemed particularly timely, given the discovery of gravitational waves by the LIGO-Virgo collaboration and the release of the Planck data in 2015, that so strongly contributed to the era of precision cosmology and to the adoption of a standard model of cosmology.
Twenty-four speakers participated in the School. We are very grateful to all of our colleagues, both to those who contributed written papers to this volume, as well as to those who participated in the School by just providing lectures. The level of the speakers was very high, with their presentations offering a broad overview of the subject matter.
The lectures were organized in a way designed to foster the interactions between two different communities. This has been, in our opinion, one of the most notable added values of the School. The School admitted more than 50 PhD students, selected from all over the world, and also some Master students of the Erasmus Joint Master Program “Astromundus”, funded by the EU and jointly provided by five European universities (Innsbruck, Gottingen, Padua, Tor Vergata and Belgrade). The environment of Villa Monastero naturally facilitates informal interactions between students and teachers. This added value of the “Enrico Fermi” Schools has been particularly important in enabling the case for integrating groups of students working in different fields and communities.
As will be obvious by going through the volume, there was a wide range of topics addressed by our lecturers. For the Gravitational Waves section, the lectures covered the experimental issues connected with gravitational wave detection and the new field of multi-messenger astronomy, as well as more astrophysical aspects. Lectures in the first category were provided by Fulvio Ricci, Viviana Fafone and Francesco Fidecaro, while the contributions of Marica Branchesi on multi-messenger astronomy and of Michela Mapelli about the open questions of black hole binaries covered the complementary aspects. In the realm of Cosmology, there are contributions on the early universe, on the Cosmic Microwave Background (CMB) and on redshift surveys. For the Early Universe, Jerome Martin provided a review of the inflationary scenarios, Sabino Matarrese discussed the non-Gaussian features of primordial density fluctuations, while Jens Chluba concentrated on the physical mechanisms responsible for the spectral distortions of the blackbody spectrum of the CMB. Regarding the CMB proper, the results of the Planck Legacy were presented by Carlo Burigana, and their theoretical implications were discussed by Douglas Scott, while the polarization modes of the CMB and the physical mechanisms underlying them were introduced by Wayne Hu. On the redshift survey side, Will Percival presented the wealth of information encoded in the large-scale structure of the universe, while David Mota reviewed the effects of modified gravity theories, with a particular focus on the effects on the non-linear regime on the structure formation process.
In conclusion, we are indebted to all our colleagues for their availability to participate in the School and for delivering outstanding lectures. We are also indebted to all the students that participated to the School with great enthusiasm and for expressing their positive opinion about the choice of the topics to which they were exposed. We are particularly thankful to the Italian Physical Society for hosting our School in the context of the program of the “Enrico Fermi” Schools, and for the professional support we received during our stay in Varenna.
Eugenio Coccia, Joe Silk and Nicola Vittorio