# Theoretical Physics at INFN Bari

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 Bari theory group is based on long traditions and covers all these and other topics.

Five main lines of *CSN 4* research are developed within the INFN special initiatives: TASP, QFT-HEP, BioPhys, NPQCD, QUANTUM.

## Astroparticle Physics and Cosmology TaSP

**Neutrino Physics and New Light Particles**

In the last two decades, the discovery of neutrino flavor oscillations (awarded with 2015 Nobel Prize) has provided us with important evidence of new physics beyond the standard electroweak model.

Although several features of the neutrino mass-mixing phenomenology can be described in a simple three-generation framework, several unknowns remain to be settled, including the absolute scale and the ordering of neutrino masses, the Dirac or Majorana nature of the neutrino fields, the precise value of the largest mixing angle, and the hints of leptonic CP violation. Moreover, besides the three known neutrinos and their standard interactions, other new light particles might play a role as messengers of new physics, including sterile neutrino states and axion or axion-like particles, possibly related also to new interaction mediators.

All these issues have profound implications in particle physics, astrophysics and cosmology. Our group is actively engaged in the theoretical and phenomenological analysis of both oscillatory and non-oscillatory aspects of standard neutrino physics, as well as on (astro)particle physics related to new light particles and

interactions, including: 1) Investigation of the neutrino CP violating phase from global data analyses of oscillation data; 2) Statistical analysis of current limits and prospective observations of neutrinoless double decay; 3) Study of neutrino mass hierarchy discrimination with atmospheric and reactor neutrinos; 4) Neutrino self-interaction and turbulence effects in Supernova neutrinos; 5) Phenomenology of new sterile neutrino states and of nonstandard interactions; 6) Axions as candidates for dark matter; 7) Bounds on axion(like) particle properties from a variety of possible astrophysical sources.

*Cosmology*

The local scientific activity in the field of cosmology is mainly devoted to the analysis of cosmological models beyond the reference one [the so-called Lambda Cold Dark matter (LCDM) model], especially to account for possible large-scale inhomogeneity and anisotropy. Recent research topics are: 1) Phenomenological discussion and a quantitative estimate of the possible relevance of the cosmological inhomogeneities of primordial origin for the precise determination of the basic parameters of the LCDM concordance model; 2) Exact, non-perturbative calculation of the redshift-luminosity distance relation, obtained in a new gauge introduced on purpose and adapted to the past light-cone of the given observer; 3) Computation (up to the third order) of the gravitational light deflection effect in perturbed cosmological backgrounds; 4) Inhomogeneous models of the Universe: Calculation of the luminosity distance of a source for off-centre observer in the LTB (Lemaitre-Tolman-Bondi) model; exact luminosity distance and apparent magnitude formulas applied to a sample data of Union2 supernovae for different profiles. Studies of electrodynamics in curved space-time, in LTB model. Effects on photon propagation in this model due to inhomogeneities.

Local coordinator: **Eligio Lisi** (INFN Bari)

## Phenomenology of the Standard Model and Beyond QFT-HEP

*Physics beyond the Standard Model, consequences in the flavor sector*

There are fundamental questions that the Standard Model (SM) of fundamental interactions leaves unanswered, namely, the number of generations of elementary fermions, the matter-antimatter asymmetry in the Universe, the nature of the dark matter, the hierarchy among the fermion masses, the vast difference between the electroweak and the Planck scale. A possible answer is that the SM is an effective field theory needing to be extended at high energies. Physics beyond the Standard Model affects rare phenomena in kaon, charm and beauty hadron physics. The group is working on the impact on flavor observables of theories with extra-dimensions and extended gauge groups. The experimental counterparts are the collaborations at LHC and at the flavor factories (BES-Beijing and Belle-Tsukuba).

*Heavy and light hadron spectroscopy*

Bound states of quarks and gluons are the prime effect of strong interactions. The experimental observations of resonances with unexpected properties, made recently at various colliders, challenge the present theoretical description, and require detailed analyses of the mass spectra and decay features. The group is providing classification schemes for the observed hadrons, as well as predictions for new states.

*Gauge/gravity duality and applications to the strong interactions*

A breakthrough in the theory of fundamental interaction is the discovery of the so-called gauge/gravity duality, which allows us to establish a correspondence between certain 4D gauge theories and higher dimensional gravity theories.The group is studying the possible application of the correspondence to strong interactions. The aim is to access hadronic quantities like masses and strong couplings, the QCD phase diagram, the temperature and baryon density dependence of the hadron properties, the evolution from far-from-equilibrium conditions of strongly interacting systems.

Local coordinator: **Fulvia De Fazio**

## Biological applications of theoretical physics methods BioPhys

Biological Theoretical Physics aims to model and discover emergent properties of biological systems, encompassing molecular factors, genomes, cells and organs, whose theoretical description is only possible at the system level, by using innovative methods and ideas coming from theoretical physics.

This is a novel, key research area in physics, triggered by the development of new quantitative, high-throughput experiments in molecular biology, where relevant, original results are expected to ground the understanding of the functioning of life on the fundamental principles of physics, with important implications in science, industry and biomedicine alike.

Our project is positioned in such a strategic, internationally growing scientific field and aims at supporting the national research community on biological theoretical physics within the INFN.

It includes a dozen different local teams working in close collaborations with each other and with a number of experimental molecular biology labs worldwide.

Responsabile locale: **Sebastiano Stramaglia**

## Non-perturbative Quantum ChromoDynamics NPQCD

The main purpose of our research program is to investigate the nonperturbative (NP) sector of Quantum Chromodynamics (QCD) using state-of-the-art numerical and analytic methods.

Quantum Chromodynamics (QCD) is the theory which describes the interactions of quarks and gluons, the elementary constituents of the matter, and how they bind together to form the hadrons we see in experiments.

A crucial, still unsolved problem of QCD, is the explanation of the color confinement, the phenomenon that quarks and gluons (color-charged particles) cannot be isolated like a photon or an electron. The phenomenon of color confinement occurs at the scale of 1 fm (the size of a hadron), where the strength of the coupling between quarks and gluons is such that nonperturbative methods (NP) are needed to make physical predictions.

In the nonperturbative study of QCD the physical observables are given in terms of functional integrals. If the continuous space-time is discretized to a finite lattice of space-time points (Lattice QCD), the functional integrals can be approximated as ordinary multidimensional integrals, even though with a huge number of integration variables. The numerical evaluation of these integrals can be done using the so-called Monte Carlo statistical methods and requires considerable computing facilities.

Our investigations are performed using state-of-the-art supercomputing resources and computational techniques, keeping also a careful eye on algorithmic developments and optimization to use at best High Performance Computing (HPC).

The study of the dynamics of QCD color confinement is of paramount importance to understand the phase diagram at high temperature and density and its deep phenomenological implications related to the physics of heavy-ion collisions, the early Universe and the astrophysics of objects like compact stars.

Local coordinator: **Leonardo Cosmai**

## Finite and infinite quantum systems QUANTUM - Entanglement, Coherence and Control

The outstanding developments of the last two decades, known as second quantum revolution, have given birth to the emerging fields of Quantum Information and Quantum Technologies.

Combined theoretical and experimental efforts, as well as the progress in simulation techniques, have led to the concrete possibility of quantum-based technological advances, with the development of devices capable of reaching unprecedented performances.

The related novel physical phenomena, as well as the astounding possibilities in controlling, addressing and manipulating single (real and artificial) atoms, atom arrays, spin systems, and superconducting circuits, and the increasing accuracy in interferometric techniques motivate novel theoretical ideas, as well as reliable and precise analyses.

The major objectives of the QUANTUM collaboration are the investigation of typical quantum mechanical effects and phenomena via three major, interrelated avenues:

1. Entanglement and other Quantum Correlations;

2. Quantum Simulation;

3. Quantum Control.

The theoretical effort is highly synergic, involving close collaborations among the partners, exchange of students, post-docs and young researchers.

The topics investigated have a foundational character, but are of interest also in view of possible applications in quantum science and technologies, as means to achieve new or radically enhanced functionalities.

**QUANTUM** focuses on the recent developments that have changed the status of quantum mechanics and made the development of Quantum Technologies the European Flagship, whose aim, as stated in the Quantum Manifesto, is “to place Europe at the forefront of the second quantum revolution now unfolding worldwide, bringing transformative advances to science, industry and society”.

National and Local coordinator: **Paolo Facchi**