Fabrizio Palumbo

Boson dominance in nuclei

We present a new method of bosonization of fermion systems applicable when the partition function is dominated by composite bosons. By restricting the partition function to such states, we obtain a Euclidean bosonic action from which we derive the Hamiltonian. Such a procedure respects all the fermion symmetries, particularly the fermion number conservation, and provides a boson mapping of all fermion operators.

Scissors mode and dichroism in an anisotropic crystal

We suggest that in an anisotropic crystal there should be a mechanism of dichroism related to a scissors mode, a kind of excitation observed in several other many-body systems. Such an effect should be found in crystals, amorphous systems, and also metalloproteins. Its signature is a strong magnetic dipole transition amplitude, which is a function of the angle between the momentum of the photon and the anisotropy axis of the cell.

Scissors Modes in crystals with cubic symmetry

AbstractWe recently suggested that the Scissors Mode (a collective excitation in which one system rotates with respect another one conserving its shape) can occur in crystals with axially symmetric atoms as a precession of these atoms around the anisotropy axis of their cells, giving rise to a form of dichroism. In the present paper we investigate how the Scissors Mode can be realized in crystals with cubic symmetry and evaluate its photo-absorption cross-section. This turns out to be of the same order of magnitude as that for crystals with axially symmetric atoms, but does not exhibit any correlation between the direction of the photon and the axes of the cell.

A two rotor model with spin for magnetic nanoparticles

We argue that a kind of magnetic nanoparticle might exist characterized by the locking of the constituent spins with the density profile of the macrospin. We represent such a nanoparticle by two interacting rigid rotors, one of which has a large spin attached to the body, namely a two rotor model with spin. By this model we can describe in a unified way the cases of nanoparticles free and stuck in an elastic or a rigid matrix. We evaluate the magnetic susceptibility for the latter case and under some realistic assumptions we get results in closed form. A crossover between thermal and purely quantum hopping occurs at a temperature much higher than that at which tunneling becomes important. Agreement with some experimental data is remarkable.

From the Pion Cloud of Tomonaga to the Electron Pairs of Schrieffer: Many Body Wave Functions from Nuclear Physics to Condensed Matter Physics

It is well known that diverse pieces of models and physical ideas coming from different areas of physics converged in the BCS theory of superconductivity. On the contrary, it is little known that the formalism developed in the Tomonaga quantum field theory of the pion-nucleon system was an important ingredient for the development of BCS theory. We discuss the evolution of these ideas in quantum field theory providing an unconventional historical perspective.

Scissors modes: The first overtone

Scissors modes were predicted in the framework of the two-rotor model. This model has an intrinsic harmonic spectrum, so that the level above the scissors mode, the first overtone, has excitation energy twice that of the scissors mode. Because the latter is of the order of 3 MeV in the rare-earth region, the energy of the overtone is below threshold for nucleon emission, and its width should remain small enough for the overtone to be observable. We find that B(E2){up_arrow}{sub overtone}=(1/64 {theta}{sub 0}{sup 2})B(E2){up_arrow}{sub scissors}, where {theta}{sub 0} is the zero-point oscillation amplitude, which in the rare-earth region is of order 10{sup -1}.

Entanglement in the states of the two-rotors model

The eigenfunctions of the Two-Rotors Model are superpositions of states corresponding to precessions of the rotors around two orthogonal axes. In Nuclear Physics such an entanglement has not been directly confirmed. We discuss how it might be observed and compare with the application of the TRM to single domain nanoparticles. In the latter case, in addition to the present indirect evidence there is the possibility of direct observation in experiments at temperatures of the order of 1 K.

Observation of scissors modes in solid state systems with a SQUID.

The occurrence of scissors modes in crystals that have deformed ions in their unit cells was predicted some time ago. The theoretical value of their energy is rather uncertain, however, ranging between ten and a few tens of eV, with the corresponding widths of 10(-7) to 10(-6) eV. Their observation by resonance fluorescence experiments therefore requires a photon spectrometer covering a wide energy range with a very high resolving power. Here, a new experiment is proposed and discussed in which such difficulties are overcome by measuring with a superconducting quantum interference device (SQUID) the variation of the magnetic field associated with the excitation of scissors modes.

Scissors modes: The elusive breathing overtone

The Two-Rotor Model predicts two levels above the Scissors Modes with degenerate intrinsic energy. They have

Composite boson dominance in many-fermion systems

J^{\pi}= 0^+,2^+