# Theoretical Physics at INFN Padova

The main goals of theoretical physics are to find fundamental laws that govern our universe, explain observed physical phenomena in nature, possibly predict new ones and, finally, make them useful for the needs of humankind. The variety of questions addressed by theorists is enormous. It ranges from the quest for understanding the very origin of the universe and its present structure, to the identification of the fundamental constituents of nature, passes on to the analysis of quantum behaviour of condensed matter systems up to tackling complex networks of physical, biological, social and technological nature. The vast spectrum of research of the Padua theory group is based on long traditions and covers all these and other topics.

Six main lines of *CSN 4* research are developed within the INFN special initiatives GSS, STEFI, AMPLITUDES, APINE, MONSTRE, NUCSYS, QUANTUM, InDARK, TASP, TEONGRAV and LINCOLN.

## Astroparticle Physics and Cosmology (InDARK, TASP, TEONGRAV)

Cosmology is the scientific discipline that studies the universe as a whole, from the very first moments of its life to its most recent evolutionary stage. We have learned that the present universe is composed not only of the stars, the galaxies and their clusters, but actually mainly of dark matter and dark energy whose nature remains a mystery. Shedding light on the Dark Side of the universe may also help to resolve other puzzles in physics of fundamental interactions. To find clues, scientists study certain cosmic messengers, such as the cosmic microwave background radiation, the light emitted by galaxies and their clusters, and very recently also gravitational waves. While photons allow us to see stars and galaxies, gravitational waves allow us to listen to the universe. In this way the universe “talks” to us via mergers of black holes or neutron stars: dramatic events, associated with enormous quantities of energy emitted via gravitational waves. InDARK, TAsP and TEONGRAV deal with all these fascinating astrophysical phenomena through a multidisciplinary approach, as is the very nature of cosmology, using theoretical, numerical and state-of-the-art data analysis methods.

Local coordinators: Nicola Bartolo (InDARK), Francesco D’Eramo (TASP), Giuliano Iorio (TEONGRAV)

## Field Theory and String Theory (GSS, STEFI)

This area of theoretical physics aims at unveiling a unified theory of fundamental interactions based on the principles of symmetries, geometry and quantum mechanics. Quantum field theory provides a unifying framework for the description of a plethora of phenomena ranging from elementary particles to condensed matter physics. This framework, however, still misses an important element, namely a consistent quantum counterpart of Einstein’s theory of gravity, which is indispensable e.g. for understanding the interior of black holes. String theory is a paradigm of a unified theory that includes quantum gravity. It is based on the assumption that the basic constituents of nature are extended objects such as strings and membranes, rather than elementary point particles. GSS and STEFI study, among other things, the rich physical and mathematical structures of this theory, as well as links between the world of strings and the phenomena we observe in nature.

Local coordinators: Gianluca Inverso (GSS), Alessandro Sfondrini (STEFI)

## Mathematical Methods (QUANTUM)

The topics studied by QUANTUM explore the foundations of the quantum aspects of nature and have direct applications in quantum science and technologies, as they form the theoretical background necessary to develop quantum computers and simulators, quantum sensors and quantum communication systems that promise to revolutionize current ICT technologies. Moreover, these novel technologies open pathways to so far unexplored research directions with potential ground-breaking applications to high-energy physics, chemistry and condensed matter, many-body systems, and quantum field theories.

Local coordinator: Simone Montangero

## Nuclear and Hadronic Physics (MONSTRE, NUCSYS)

MONSTRE implements an integral approach to the study of the physics of atomic nuclei, nuclear reactions, and strongly interacting matter, by matching the development of the theory of nuclear structure and reactions with the experimental progress currently underway in the rare isotope production, the physics of strong and electroweak interactions, and nuclear astrophysics. To this end a set of advanced many-body analytic and computational methods is being developed.

NUCSYS uses modern scattering techniques combined with theoretical methods in cluster dynamics to study nuclei far from stability, in particular weakly-bound or unbound light and medium nuclei. It models various new unstable nuclear systems that can be studied with the Rare Isotope and Radioactive Ion Beam (RIB) facilities. NUCSYS also provides theoretical support and guidance to strategic INFN-Labs projects of nuclear applications, such as the production of innovative radio-nuclides and radio-labelled compounds for advanced medical therapies and diagnostics.

Local coordinators: Lorenzo Fortunato (MONSTRE), Luciano Canton (NUCSYS)

## Phenomenology of Elementary Particles (AMPLITUDES, APINE)

The goal of particle physics is to investigate the nature of the basic constituents of matter and to understand how they interact. On the one hand, we perform theoretical studies within the so-called Standard Model of fundamental interactions, a very successful theory describing all microscopic phenomena observed so far. We predict and analyse the outcome of experiments performed at high-energy and at high-intensity of particle beams, developing new methods for the most precise predictions. On the other hand, since the Standard Model leaves unanswered several fundamental questions, such as the origin of particle masses or the nature of dark matter, we also construct possible extensions of the Standard Model investigating their experimental signatures in new experiments. APINE provides the necessary theoretical support to such experimental efforts. To achieve this important aim, our approach is interdisciplinary, multi-pronged and touches upon the three frontiers: High Energy, High Intensity and Astroparticle Physics.

High energy particle collisions are the ideal framework for accessing new information on matter constituents and forces of Nature. Advances in Theoretical Physics depend on our ability to describe the scattering processes involving many light and heavy particles at very high accuracy. A convenient way to represent particle collisions is by means of Feynman diagrams, drawing pictures of the various ways particles can transform or mix during an interaction. This approach, very surprisingly, turns out to be applicable also to the description of astrophysical phenomena, like the gravitational collapse of a binary system of massive objects, such as a black-hole/neutron-star pair, which, after merging, give rise to Gravitational Waves. Algorithmic implementation of novel computational ideas, simulations and large scale calculations benefit from profound mathematical concepts and from the novel strategies emerging in Computer Science, Data Science, and AI. The research of AMPLITUDES in this area is highly interdisciplinary and open to new applications and new contaminations from other fields of Natural and Social Sciences.

## Statistical and Applied Field Theory (LINCOLN)

Complex networks are nowadays ubiquitous in various research areas such as the physics of soft materials, cell biology, neuroscience, epidemiology, and machine learning. Examples include quantum networks which are an important element of quantum computing and quantum communication systems, contact networks in proteins and chromatin, ecological and social networks, metabolic networks, transportation networks and neural networks. LINCOLN explores their statistical properties and looks for potential applications in quantum mechanics, social life, information theory and biology by using advanced theoretical tools, state-of-the-art numerical techniques and modern data analysis.

Local and national coordinator: Enzo Orlandini