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Origin of (dynamical) mass in visible universe and hadron properties in nuclear medium

Grant number: 19/00763-0
Support type:Regular Research Grants
Duration: August 01, 2019 - July 31, 2021
Field of knowledge:Physical Sciences and Mathematics - Physics
Principal Investigator:Kazuo Tsushima
Grantee:Kazuo Tsushima
Home Institution: Pró-Reitoria de Pós-Graduação e Pesquisa. Universidade Cruzeiro do Sul (UNICSUL). São Paulo , SP, Brazil
Assoc. researchers:Gastão Inácio Krein ; Gilberto Tomás Ferreira Ramalho

Abstract

The project aims to explore the properties and structure of strongly interacting particles, known as hadrons, in free space (vacuum) and in medium (many nucleon and/or hadron environment).The objectives we deal with are the quarks, gluons, hadrons, and (hyper)nuclei, where thedynamics of strong interaction for the quarks and hadrons, and the origin of dynamicallygenerated masses, namely more than 90% of the proton and neutron (hadrons) masses, isdescribed by a local gauge theory, quantum chromodynamics (QCD).The discovery of the Higgs boson by the experiments with the large hadron collider (LHC)in CERN, has now fully established the Standard Model (SM). In the SM the mechanism ofspontaneous symmetry breaking plays a crucial role. The spontaneously broken vacuum getsnon-zero vacuum expectation value (Higgs-doublet field), and this gives the bare masses of allthe massive particles in the SM, namely the quarks, leptons and the massive gauge bosons. TheStandard Model unifies the description of electromagnetic and weak interactions, and explains three of the four fundamental forces of nature, namely, the strong, electromagnetic and weak interactions.On the other hand, the mass of the visible Universe, is carried by protons, neutrons andatomic nuclei, which are not elementary. Their masses are the result of the strong force actingbetween quarks and gluons, which is described by QCD. The dynamical symmetry breakingdue to the strong interaction dictated by QCD (trace anomaly), gives more than 90% of hadronmasses. Since hadrons, including the protons and neutrons which form the core of nuclei andatoms around us, interact strongly and are made of quarks and gluons, and the dynamics ofthese quarks and gluons is described by QCD. Thus QCD is responsible for explaining most ofthe mass of the "visible Universe" (carried by protons, neutrons and atomic nuclei).Although QCD is believed to be the theory of the strong interaction describing the dynamics of quarks and gluons inside hadrons and between hadrons, the hadrons show muchricher, unexpected features which emerge from QCD but cannot be easily understood in termsof it. This feature becomes particularly evident when hadrons are immersed in medium, or surrounded by many hadrons. Thus, we are especially interested in the dense matter, the matter exists in the center of a large mass nuclei (e.g., a led nucleus), the core of neutron star, or the matter produced in high-energy heavy ion collisions.The matter (hadrons) in our universe gets most of its physical masses in free space throughthe spontaneous breaking of chiral symmetry and confinement (dynamical symmetry breakingin QCD). Importantly, this spontaneously broken dynamical symmetry is believed to be restoredpartially in medium with high hadron density and/or temperature (partial restoration of chiralsymmetry). As a consequence, the masses and the properties of hadrons are expected to bemodified in medium, and this is supported by several experimental facts and/or evidence, suchas the EMC effect, the observed changes of bound proton electromagnetic form factors, and theformation of quark-gluon plasma phase. Thus, the core of the project is, to study the quarkand gluon structure of hadrons both in free space and especially in medium, which play animportant role in understanding the existence of matter (mass) in our "visible Universe". (AU)