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Scientific Report 2007-2009
Theoretical physics
interest. Some recent results provide a generalization of the Noether theorem that can be applied
to the Hops algebra symmetries of non-commutative spacetime, and some recent studies of the
phenomenology of the problem are using these results.
We hope, to make a long story short, that the research of our group will eventually help to shed
light on the fascinating mystery of Quantum Gravity.
This last research argument is bringing us smoothly toward our Theoretical Astrophysics
(here relation with the Astronomy and astrophysical group of our Department are strong and
important: see the related report for useful additional information), and again we will start by
describing a research that crosses over from phenomenology of elementary particles to astrophysics:
“Particles in Astrophysics: UHECR maps versus UHE Tau Neutrinos” [T7]. There is not yet
a proven correlation between cosmic rays and astronomical maps, mostly because of magnetic
bending and blurring. Since more than half a century however the cosmic ray spectra extended
up to ultra high energy regions, UHECR: at these energies Lorentz bending becomes negligible,
and UHECR are no longer constrained in our own galaxy. Our group studies UHECR since two
decades. This offers a natural window into the highest energy astronomy in the universe.
Gravitational waves are the (missing) crucial link to a consistent description of Quantum Gravity,
and the work described in [T8], “Physics of Gravitational Wave Sources” moves in this direction.
The first generation of interferometric detectors of gravitational waves is now operating at the
design sensitivity: the European detectors VIRGO and GEO and the American experiment LIGO
are taking data which will be analyzed in coincidence. Update of these detectors already started,
and the second generation detectors will enhance their sensitivity by an order of magnitude: a
design study for a further, third generation of detectors is in progress. The researchers of our group
analyze various different theoretical aspects of the physics of gravitational waves astrophysical
sources. The main topics are: (1) non radial oscillations and instabilities of neutron stars; (2)
interaction of stars and black holes in binary systems; (3) structure and deformations of strongly
magnetized neutron stars; (4) stochastic background of gravitational waves. These four research
subjects are of crucial importance. In relation to point one our group has shown that a gravity wave
detection from a pulsating star will enable researchers to establish whether the emitting source is a
neutron star or a quark star. For the second issue our researchers have studied the tidal disruption
of neutron stars by black holes in coalescing binars. For point three a general relativistic model of
magnetars has been proposed. Last, for point four, the study of the gravitational wave stochastic
background generated by Population III and Population II stars has been completed.
Detecting and understanding gravitational waves is, nowadays, one of the crucial goals of physics,
and our group will surely continue giving important contributions in this direction.
Three other subjects are very important and are investigated by our group: (1) the “Gamma-
Ray Bursts” [T9]; (2) the “Massive Nuclear Cores, Neutron Stars and Black Holes” [T10]; (3)
“Quantum Cosmology” [T11]. As far as point one is concerned, using the observed gamma ray
burst data the researchers of our group have progressed on the understanding of a theoretically
predicted gamma ray burst structure, as composed by a proper gamma ray burst and an extended
afterglow. For point two we are concerned with the study of nuclear cores, neutron stars and
black holes. Here one wants to describe the process of gravitational collapse leading either to the
formation of a neutron star or to the birth of a back hole. The researchers of the group establish
that the electron density distribution deviates from the proton density distribution at the nuclear
density: they find a stable and energetically favorable distribution of electrons. They study the
energy states of electrons in the Coulomb potential and calculate the rate of the electron positron
production. As far as the third issue is concerned, the center is the investigation of cosmological
models with a minimal scale. The researchers of the group have analyzed the polymer representation
of quantum mechanics for a particular homogeneous cosmological space-time. Also the
Bianchi IX cosmological model (the Mixmaster Universe) has been studied within the framework
of the generalized uncertainty principle. We also want to quote the problem of a background
independent quantization of the gravitational field in a generic local Lorentz frame and the study
Sapienza Università di Roma 21 Dipartimento di Fisica