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Scientific Report 2007-2009
Theoretical physics
The Theory Group
The Theory Group of the Physics Department at “La Sapienza” has produced, in the last many
years, a large number of relevant results and, probably, among its main achievement there has
been the ability to produce important and useful bridges, connecting different fields, unifying ideas
and techniques and developing synergies that have allowed different parts of theoretical physics
to progress fast.
Permanent members of the Theory group are 24 Full Professors, 9 Associate Professors and 11
Assistant Professors: many post-doctoral fellows and PhD students work with our group, and are
supported both by Italian and by European funding.
Different historical developments of Renormalization Group that have been based here are probably
the best example for qualifying this kind of developments: researchers working in particle
physics have been talking to researchers trying to understand problems in condensed matter
physics, finding common ground for important developments. On more general ground developments
in Field Theory and Statistical Mechanics, for example, have been important, together
with ideas whose reach has led, among others, to developments in computational physics and in
biophysics.
In this sense I should start by making clear that I describe here only one part of the activities
of our Department in Theoretical Physics: an equally important part is described in the Section
about “Condensed Matter Physics and Biophysics”, and the links among these different parts are
really crucial. Let me quote, among other important subjects, the physics of strongly correlated
systems, of high T c superconductivity, of cooling and Fermi-Bose atomic mixtures of chaos and
turbulence, of molecular dynamics, of self organized criticality and complexity (also applied to
contexts far from the classical realm of the physics, as for example social dynamics or natural
languages), and of different theoretical issue in biophysics. All these subjects are investigated
in our Theory Group, and are discussed in this Report in the “Condensed Matter Physics and
Biophysics” Section. The contributions C1-3, C7, C9-22, C38 and C44 that are described there and
about which Francesco Sciortino comments are indeed, exactly as the ones on which we comment
here, part of the work of the Theory group.
It is also important to note, before going to some detail, that the Theory Group researchers
have been awarded a number of prestigious prizes and awards: I will only remind the reader, as a
crucial example, that the group includes two Dirac medalists and that to its members have been
awarded two Boltzmann medals.
I will describe here four main lines of research that, when considered together with the ones
discussed in the Condensed Matter report, characterize well the large scope of the interest of our
researchers. I will discuss here about our researches on the Physics of Fundamental Interactions,
on Theoretical Astrophysics, on the Physics of Disordered and Complex Systems
and on Mathematical Physics. There are a lot of ambiguities in this division, and many contribution
span indeed more than one of these subsets, but I feel that this rough indexing (when,
I repeat, seen together with the Theory researches described in the condensed matter section) is
useful to give the lines of a short summary.
Let us start with our contributions to the Physics of Fundamental Interactions. The
first part we want to stress is the phenomenological analysis of elementary particles. “The New
hadrons” [T1] contribution to this report starts from noticing that although bound states of more
than three quarks are in principle compatible with Quantum Chromodynamics, at today there is
no clear evidence of the existence of such states. A collaboration of theorists and experimentalists
has reanalyzed experimental data to produce a consistent picture. In particular this group has
worked on trying to establish if there is evidence for tetra-quark, i.e. bound states of a di-quark
(an agglomerate of two quarks) and an anti-di-quark. Two papers of this group have established
Sapienza Università di Roma 19 Dipartimento di Fisica