S. Esposito's scientific activity

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Neutrino Physics In his first paper, published before he graduated in Physics, he showed how the MSW theory of neutrino oscillations in matter may effectively solve the problem of the solar neutrino deficit. After his graduation, he continued to work of Neutrino Physics, researching on flavor and Pontecorvo oscillations in vacuum, in matter and in presence of a magnetic field. In particular, in collaboration with G. Capone, he studied the propagation of massive neutrinos in magnetized dense media. Such a study has been the basis for the possible understanding of the high pulsar velocities according to the Kusenko-Segrè mechanism and further generalizations. Furthermore, in collaboration with several researchers, he performed a comprehensive investigation on the observable effects induced by neutrino oscillations on the energy spectra of neutrinos emitted by Supernovae (both with and without taking into account possible electromagnetic interactions of such particles). This study will be particularly useful in the detection of Supernova explosions by precise neutrino detectors. He has also proposed (in collaboration with G. Salesi) a simple phenomenological interpretation of several, apparently conflicting, data coming from neutrino oscillations laboratory experiments. The theoretical model proposed, able to predict quite detailed observations effectively measured, points toward a non-negligible CPT symmetry violation in neutrino oscillations.

Physics of the primordial Universe One of his major contributions has been in the field of the nucleosynthesis of light elements in the primordial Universe, in collaboration with G. Mangano, G. Miele and O. Pisanti. First of all, a consistent procedure has been introduced in order to evaluate wave-function renormalization of particles in an heat bath at given temperature. Then, an accurate and comprehensive study of all the physical effects concurring in the primordial nucleosynthesis has been conducted, aimed to give accurate phenomenological predictions on the relative abundances of the light element in the Universe. From this study, a complex and very precise numerical code has been elaborated in order to obtain the numerical values of such abundances (once the parameters of the theory are fixed). Subsequently, an analysis of the available experimental data, both on the light element yields and on the anisotropies of the cosmic background radiation, has been performed comparing them with the theoretical predictions, and giving some constraints on the standard theory of the primordial nucleosynthesis. At the same time it has been conducted a study on the distortions of the cosmic background radiation spectrum, induced by a non vanishing chemical potential for neutrinos during the development of the primordial nucleosynthesis. The copious and important results obtained in this field are currently and largely used by the international scientific community. Finally, he has also studied the phenomenological consequences of a Lorentz symmetry violation at the level of the particle energy-momentum dispersion relations. From this study, the first experimental limits on some theoretical parameters has been deduced, pointing out also the implications of Lorentz violation on cosmological scales.

Tunnelling photon effect Some questions have been studied regarding the tunnel effect of photons in peculiar experimental setups. These questions have arisen in connection to recent observations of light signals propagating (in the mentioned setups) with a group velocity higher than the speed of light in vacuum. He has showed how such observations are not conflicting with the Principle of Relativity and that, moreover, they are well described by Quantum Mechanics. Such results are usually employed in the international laboratories studying this phenomenon. Recently, a detailed study devoted to find the general physical conditions under which photonic Klein tunneling (i.e. with an arbitrarily large transmission coeficcient) takes place has been performed. The key role of spontaneous emission of photons has, then, been studied accurately, while giving specific predictions in one case of particularly relevance for applications.

Field Theory Besides the studies about Lorentz symmetry violation, already mentioned above, he has worked on the interactions between a Kalb-Ramond field and ordinary matter fields, and the proposed model has been applied to some kinds of superconductors. Further theoretical researches on peculiar superconductors has been performed, in collaboration with E. Di Grezia and G. Salesi, predicting novel properties for such physical systems which are worth to be detected experimentally. The study of the phenomenological predictions of the theoretical models proposed has then allowed to give a thorough qualitative and quantitative explanation of several non-standard properties shown by non-conventional superconductors, which are effectively observed. It is quite remarkable that such properties had not yet found previously a consistent systematization in the existing theoretical frameworks. His innovative works on superconductors have earned him the Majorana medal from EJTP in 2008.

Theoretical Physics (other topics) In collaboration with M.W. Evans and E. Recami, he has developed a theory for the phenomena of fermion resonance in atomic systems induced by electromagnetic radiation rather than by static magnetic fields, giving some precise experimental predictions. He has also conducted studies on fundamental questions of Electrodynamics, giving a covariant formulation (particularly acknowledged by the scientific community) of the Majorana-Oppenheimer-Romer theory of electromagnetism, and of Quantum Mechanics, pointing out how true quantum effects are strictly related with the spin of the particles and deriving, in this framework, the usual probabilistic interpretation. Assisted by two student of him, he has performed several accurate experiments on the so-called Mpemba effect, that is, the freezing of initially hot water before that of initially cold one. In fact, although such an effect has been observed since long time, no satisfactory explanation for it has been so far provided. Based also on the experimental results obtained, he has successfully proposed a quantitative explanation of the Mpemba phenomenon in terms of two major effects: supercooling and the appearance of (three) phase transitions before the freezing point. Such phases involve different ordering of clusters of molecules in water, and only two transitions of these have been previously observed. These observations have been subsequently confirmed by other experiments performed in different international laboratories. In collaboration with V. Capano and G. Salesi, he has detected quite an unexpected phenomenon taking place in highly viscous media, that is the formation of a well-defined metastable structure due to the mechanical perturbations (such as, for example, the falling of a steel sphere in glycerol). The accurate experimental studies, though preliminary, has allowed the development of a theoretical model for such non-trivial phenomenon, which is currently under study also due to its potential technical applications. He has also applied methods and results of the quantum theory of fields to the study of phenomena relevant for condensed matter physics, including Majorana fermions and graphene. More in detail, he studied the interactions of Majorana fermions in nanowires coupled to superconductors and mediated by a non-vanishing anapole magnetic moment. Such a study has brought to the development of an ingenious method able to distinguish univocally the presence of Majorana fermions from that of Weyl fermions in condensed matter systems. Concerning the study of light transmission in graphene when an applied magnetic field is present, he discovered a peculiar threshold effect about minimum transmission showed by such systems, which is ruled by the applied field. Also, in collaboration with the University of Bergamo, he developed an accurate protocol (ThermoTex) for testing the thermal properties of (dry and wet) textile fabrics, which is well suited for optimizing the thermal comfort of fabrics, according to the UNI EN 31092 standard. In collaboration with theoretical and experimental groups of the University of Bergamo and of the INFN National Laboratories in Catania, he studied the possible formation of complex structures in pure water and in aqueous solutions of silica gel (TEOS). He analyzed the experimental data obtained from the experimental technique based on the observation of delayed luminescence, by pointing out particular unknown properties of water. Finally, a particular mention deserves his demanding, as well as highly requested, activity as a reviewer of articles on theoretical and mathematical physics for the database Mathematical Reviews of the American Mathematical Society.

Popular Physics His prolonged experience acquired by teaching in secondary schools, as well as his continued collaboration with the Museum of Physics at the University of Naples "Federico II", allowed him to provide significant contributions in the field of popular science and Physics teaching, appreciated both nationally and internationally. In addition to his popular physics papers on special topics (such as, for example, measurements of astronomical interest, or simple problems of astrophysics), particularly relevant is his popular seminar activity, both on general topics (mechanics, electromagnetism, history of physics, etc.) and on particular issues (quantum physics, nuclear and subnuclear physics, turbulent fluid dynamics, etc.), aimed primarily at students. Particularly appreciated is his design and construction activity (with the collaboration of high school and/or university students) of scientific instruments of popular and historical interest, for the Museum of Physics in Naples or high schools: Galileo's inclined plane; Stevin's inclined plane; demonstration unit for Galileo's law of chords; set of pendulums system for the verification of isocronism; set of coupled pendulums for the study of the resonance phenomenon; set of "entropic" pendulums for the study of disorder and chaos; mechanical random events generator; automatic hourglass for the illustration of the working principles of heat engines, etc. Finally, also noteworthy is his work as a reviewer of scientific and popular books, which has been particularly successful in the international arena.

History of Physics His major contribution related to the field of the history of Physics concerns the accurate study of the unknown works by Ettore Majorana. The published, known papers by one of the greatest theoretical physicists of the XX century, according to Enrico Fermi, are only a few, while the unpublished ones are very numerous. In 2003, in collaboration with E. Majorana jr., E. Recami and A. van der Merwe, a book has been published (by Kluwer/Springer) with the English translation of part of the Majorana's works known, in Italian, as "Volumetti" (while the Italian edition has been published in 2006 by Zanichelli, in occasion of the centenary of the birth of Majorana). In this text (accounting for a total of about 500 pages), besides usual topics developed in a very original manner, several frontier research topics appear, whose treatment presents an enormous interest and usefulness even at more than 70 years later. Subsequently, in collaboration with R. Battiston, A. van der Merwe and E. Recami, he has also prepared the English translation of some other unpublished research notes by Majorana, containing material of considerable scientific and historical interest excerpted from the 18 "Quaderni" (research notebooks) by Majorana. It has been published in 2009 by Springer. Other major works have been devoted to the study of the role played by Majorana on the understanding of some peculiar topics, such contributions being previously unknown due to the fact that they were never published by the great scientist. Just to quote one only example, this is the case of the study of the atomic model by Thomas and Fermi, where Majorana introduced an interesting method for the solution of the differential Thomas-Fermi equation (now particularly appreciated by the scientific community), which has been further recognized as useful also in obtaining the solution of an entire class of differential equation appearing in physical applications. The entire set of the accurate historical and scientific researches about the published and unpublished works by Majorana then converged in the publication (2015) of an exhaustive book for the Cambridge University Press. Two chapters are present in this volume pointing out the current applications of Majorana's results, and written by Evgeny Akhmedov and by the Nobel Laureate (Physics, 2004) Frank Wilczek, respectively. Then, in collaboration with A. Drago, in 2004 he has discovered the existence of the text of six unknown lecture notes (out of the ten known ones) prepared for the course on Theoretical Physics delivered by Majorana at the University of Naples in 1938, just before his mysterious disappearance. This has been achieved with the recovery of the so-called "Moreno Paper", where all the lectures delivered by Majorana have been reported by a student of him. The entire set of Majorana's lectures has been published in 2006 by Bibliopolis (in the original Italian version). The detailed scientific, historical and biographical studies about Ettore Majorana, as well as accurate in situ investigations, have then allowed him to reconstruct in quite a detail the story related to the mysterious disappearance of that scientist in 1938. This comes together in a popular book published in 2009 by Liguori, which has provoked large interest in Italy and abroad. Besides the researches about Majorana's work, in recent year he has also been involved (in collaboration with M. Leone, and on behalf of L. A. Radicati of the Scuola Normale Superiore in Pisa) in the cataloguing and study of the documents conserved at the Wick Archive at the Library of the Scuola Normale Superiore in Pisa, where letters, notes and books by Gian Carlo Wick are conserved. This study has been mainly devoted to the study of the (scientific and non scientific) correspondence of the mentioned scientist. Finally, the retrieval of novel documents regarding the work by Enrico Fermi about the construction and development of the first nuclear reactors (and of the atomic bomb) has allowed an accurate study of the role played by the Italian scientist in such projects which, in some respects, reveals particularly interesting and unexpected characteristics. A book by World Scientific (in collaboration with O. Pisanti) appeared in 2010, where some of this material is reported.