!!Djordje Sijacki
!Short laudatio by A.W. Wolfendale
Djordje Sijacki made a significant contribution at the international level
in the fields of symmetry groups representation theory and the symmetry based approach to
particle physics and gravity theories.
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Sijacki is the world leading expert in the subject of the quantum mechanical
representations of the SL(n,R) groups. There was a long standing problem in physics and mathematics
literature about existence and the form of their spinorial representations. Sijacki
succeeded to find the complete solution of the (infinitely many) infinite-dimensional unitary
irreducible representations of SL(3,R) and SL(4,R), which was acknowledged by leading
mathematicians as well. Recently, he achieved to generalize the Gell-Mann Lie algebra
decontraction formula and extended the explicite closed-form solution of the non-compact matrix
elements for all infinite-dimensional representations to the general SL(n,R) case, thus
making an important breakthrough in a few decades old subject.
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Sijacki generalized the algebraic approach to hadron resonances spectroscopy
of Dothan, Gell-Mann and Ne'eman to the relativistic case and developed the Affine
Symmetry model that fits notably with the experimentally observed Regge trajectories of
hadronic resonances. Furthermore, with Yuval Ne'eman, he proposed the "Chromogravity" theory,
an effective description of the QCD theory in the Infra-Red region based on the colorless
di-gluon configurations. He showed that the IR sector of the QCD gauge can be described
by a pseudo Generalized Coordinate Transformations, and thus he developed a pseudo-gravity
formulation of the confining QCD sector. His research on Chromogravity yields a QCD
based dynamical explanation of the Regge trajectories of hadrons and provides their previously
known famous linear spin vs. mass-squared relation.
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Sijacki played an important role in development of the Metric-Affine, i.e.
Gauge-Affine, generalization of Einstein's General Relativity theory in
the quantum region. He succeeded to construct a realistic model, with a spontaneous symmetry
breaking scenario, that reduces to the Poincare gauge theory of gravity. He showed that the
Einstein's world tensor notion can be extended to the generic curved space "world spinors"
as well by making use of the infinite-component GL(4,R) spinorial matter fields (there are
no such finite fields).
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He achieved an explicite construction of the world spinor fields, and managed
recently to amplify the result by generalizing the famous Dirac equation to an infinite-component
equation in a generic curved space. In particular, he provided an explicite
solution in the 3D case, thus provided for the first time a Dirac-like equation for the General
Coordinate Transformations spinors. Moreover, Sijacki extended the gravity world spinor
constructions to the case of the spinning p-branes objects in a generic curved space.

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