arXiv subjects
Publications and source records attributed to E. Di Grezia.
A theoretical model describing neutron-proton scattering developed by Majorana as early as in 1932, is discussed in detail with the experiments that motivated it. Majorana using collisions' theory, obtained the explicit expression of solutions of wave equation of the neutron-proton system. In this work two different models, the unpublished one of Majorana and the contemporary work of Massey, are studied and compared.
We propose a simple explanation of unconventional thermodynamical and magnetic properties observed for Sr2RuO4. Actually, our two-phase model of superconductivity, based on a straight generalization of the Ginzburg-Landau theory, does predict two jumps in the heat capacity as well as a double curve for the dependence of the critical temperature on an external magnetic field. Such theoretical previsions well agree with the currently available experimental data for Sr2RuO4
We investigate the black hole thermodynamics in a "deformed" relativity framework where the energy-momentum dispersion law is Lorentz-violating and the Schwarzchild-like metric is momentum-dependent with a Planckian cut-off. We obtain net deviations of the basic thermodynamical quantities from the Hawking-Bekenstein predictions: actually, the black hole evaporation is expected to quit at a nonzero critical mass value (of the order of the Planck mass), leaving a zero temperature remnant, and avoiding a spacetime singularity. Quite surprisingly, the present semiclassical corrections to black hole temperature, entropy, and heat capacity turn out to be identical to the ones obtained within some quantum approaches.
We show that, despite of the reparametrization symmetry of the Lagrangian describing the interaction between a scalar field and gauge vector bosons, the dynamics of the Higgs mechanism is really affected by the representation gauge chosen for the Higgs field. Actually, we find that, varying the parametrization for the two degrees of freedom of the complex scalar field, we obtain different expressions for the Higgs mass: in its turn this entails different expressions for the critical temperatures, ranging from zero to a maximum value, as well as different expressions for other basic thermodynamical quantities.
We succeed to build up a straightforward theoretical model for spin-triplet p-wave superconductors by introducing in Ginzburg-Landau theory a second order parameter and a suitable interaction between the two mean fields.
We have recently proposed a theoretical model for superconductors endowed with two distinct superconducting phases, described by two scalar order parameters which condensate at different critical temperatures. On analyzing the magnetic behavior of such systems, we have found some observable differences with respect to the case of ordinary Ginzburg-Landau superconductors. In particular, at low temperature the London penetration length is strongly reduced and the Ginzburg-Landau parameter k becomes a function of temperature. By contrast, in the temperature region between the two phase transitions k is constant and the system is a type-I or a type-II superconductor depending on the ratio between the critical temperatures.
The recently proposed theoretical model of superconductors endowed with two distinct superconducting phases and critical temperatures is further analyzed by introducing two distinct order parameters, described by two scalar fields which condensate at different temperatures. We find some deviations in basic thermodynamical quantities with respect to the Ginzburg-Landau one-phase superconductors. In particular, by contrast to the usual case where only one jump in specific heat takes place at the normal-superconductor transition temperature, we actually predict an additional discontinuity for C_V when passing from a superconducting phase to the other one.
A complete theoretical model describing artificial disintegration of nuclei by bombardment with alpha-particles, developed by Majorana as early as in 1930, is discussed in detail alongside the basic experimental evidences that motivated it. By following the quantum dynamics of a state resulting from the superposition of a discrete state with a continuum one, whose interaction is described by a given potential term, Majorana obtained (among the other predictions) the explicit expression for the integrated cross section of the nuclear process, which is the direct measurable quantity of interest in the experiments. Though this is the first application of the concept of quasi-stationary states to a Nuclear Physics problem, it seems also that the unpublished Majorana's work anticipates by several years the related seminal paper by Fano on Atomic Physics.
We analyze the phenomenological consequences of a Lorentz violating energy-momentum dispersion relation in order to give a simple explanation for the baryon asymmetry in the Universe. By assuming very few hypotheses, we propose a straightforward mechanism for generating the observed matter-antimatter asymmetry which entails a Lorentz-breakdown energy scale of the order of the Greisen-Zatsepin-Kuzmin cut-off.
We propose a simple model for superconductors endowed with two critical temperatures, corresponding to two second-order phase transitions, in the framework of the Ginzburg-Landau mean-field theory. For very large Cooper pair self-interaction, in addition to the standard condensation occurring in the Ginzburg-Landau theory, we find another phase transition at a lower temperature with a maximum difference of 15% between the two critical temperatures.
An account is given on the first studies on the physics of ammonia, focusing on the infrared spectra of that molecule. Relevant contributions from several authors, in the years until 1932, are pointed out, discussing also an unknown study by E.Majorana on this topic.
Quantitative bounds on Lorentz symmetry violation in the neutrino sector have been obtained by analyzing existing laboratory data on neutron $β$ decay and pion leptonic decays. In particular some parameters appearing in the energy-momentum dispersion relations for $ν_e$ and $ν_μ$ have been constrained in two typical cases arising in many models accounting for Lorentz violation.
We give a straightforward generalization of the Ginzburg-Landau theory for superconductors where the scalar phase field is replaced by an antisymmetric Kalb-Ramond field. We predict that at very low temperatures, where quantum phase effects are expected to play a significant role, the presence of vortices destroys superconductivity.
We study symmetry of space-time in presence of a minimally coupled scalar field interacting with a Kalb--Ramond tensor fields in a homogeneous but initially anisotropic universe. The analysis is performed for the two relevant cases of a pure cosmological constant and a minimal quadratic, renormalizable, interaction term. In both cases, due to expansion, a complete spatial symmetry restoration is dynamically obtained.
We give an account of the appearance and first developments of the statistical model of atoms proposed by Thomas and Fermi, focusing on the main results achieved by Fermi and his group in Rome. Particular attention is addressed to the unknown contribution to this subject by Majorana, anticipating some important results reached later by leading physicists.
We study the direct interaction of an antisymmetric Kalb-Ramond field with a scalar particle derived from a gauge principle. The method outlined in this paper to define a covariant derivative is applied to a simple model leading to a linear coupling between the fields. Although no conserved Noether charge exists, a conserved topological current comes out from the antisymmetry properties of the Kalb-Ramond field. Some interesting features of this current are pointed out.