arXiv subjects

Alessandro De Angelis

Publications and source records attributed to Alessandro De Angelis.

At least 19 recordsLinked to original sources

arXiv2026

MeV-GeV Gamma-Ray Astrophysics in the Multimessenger Era

Gamma-ray astrophysics probes the most extreme particle accelerators and explosive transients in the Universe. From pioneering theoretical predictions in the 1950s and the first space-borne detections in the 1960s, mostly exploring the sub-MeV region, the field has evolved into a mature, multi-decade enterprise that spans nine orders of magnitude in photon energy up to PeV energies and interfaces naturally with neutrino and gravitational-wave astronomy. Yet the energy range from a few hundred keV to a few GeV -- the "MeV gap", constraining progress on nucleosynthesis, positron annihilation, transient physics, dark-matter signatures, and electromagnetic counterparts to high-energy neutrinos and gravitational waves - remains sensitivity-limited. In this paper, we survey the scientific motivations for gamma-ray astrophysics, sketch a concise history from the first ideas to key milestones in space- and ground- based gamma-ray astronomy, and discuss programmatic attempts to close the MeV gap.

physics.gen-ph↗

arXiv2025

Causality in Physics: From Galileo to Einstein, and Beyond

Causality is one of the most fundamental -- and yet elusive -- concepts in physics. From its intuitive role in everyday experience to its formal and often implicit role in scientific theories, causality has challenged philosophers and physicists alike. In what follows, we take a brief historical and conceptual journey through classical and modern physics, tracing how causality has been treated, questioned, or protected in successive physical frameworks -- from Galilean mechanics to Newtonian dynamics, from Lagrangian and Hamiltonian formulations to special and general relativity, and finally to quantum mechanics and statistical physics. Our aim is to show how the notion of causality has repeatedly receded into the background of our most successful theories, even when it appears to be central to our everyday understanding of the world.

physics.pop-ph↗

arXiv2025

Ugo Amaldi, the DELPHI Collaboration and The Physics Legacy of LEP

This article offers a portrait of the DELPHI experiment at CERN's Large Electron-Positron Collider (LEP) through the scientific life and leadership of Ugo Amaldi. It traces how DELPHI contributed to LEP's physics program, from precision studies at the Z pole to higher-energy running with W-pair production and increasingly ambitious Higgs searches. Along the way, it highlights Ugo Amaldi's technical and organizational innovations, especially his insistence on bold detector choices and his sustained support for young physicists and collaborative leadership. The article also recalls Ugo's influential work on the unification of forces and shows how DELPHI's technologies, software, governance structures, and data-sharing practices anticipated many features of later collider experiments and of contemporary science policy. In this sense, DELPHI's legacy is not only foundational for today's particle physics, but also a lasting and formative element of modern scientific culture.

physics.hist-ph↗

arXiv2025

Galileo Galilei and Satellite Navigation

In 1492, for the first time, an unknown ocean opened up before sailors: weeks of navigation and no idea how to pinpoint their location. Since ancient times, navigators had known how to determine latitude by using the North Star, but the "problem of longitude" was different. More than a century later, Galileo Galilei discovered in Padua Jupiter's satellites and quickly realized that a sailor who could observe their eclipses would know his own longitude. Yet his brilliant insight was 400 years ahead of the technology of his time. Impractical at sea, on land this idea became a formidable tool for cartography and ushered in the age of the image of the world. Today the technique can be realized thanks to artificial satellites, and the Tuscan genius' name has reached space with the European satellite system named Galileo. An exhibition in Paris, organized by the Permanent Representation of Italy to the International Organizations, Sorbonne University, and the Galileo Museum in Florence, and directed by Asia Ruffo di Calabria of the Musee des Arts et Metiers, by Quentin Cheval-Galland of the Sorbonne University, and by Alessandro De Angelis, allowed visitors to observe inventions of the time and some writings by Galileo on the theme of geolocation. The exhibition was held in Paris in June 2024. It was replicated in Prague in October 2024, in Amsterdam in December 2025, and at the Perimeter Institute in Waterloo, Canada, in February 2025.

physics.hist-ph↗

arXiv2023

Galileo Galilei and a forgotten poem on the 1604 supernova

In October 1604, when SN1604, the last naked-eye visible supernova in our Galaxy, exploded, Galileo Galilei was the professor of mathematics and astronomy at the University of Padua, teaching the mechanics of planets. He was therefore the figure of reference to whom all the doubts and questions that such an apparition brought with it were addressed. The University of Padua asked Galilei to outline the situation by exposing in three public conferences his point of view in order to answer the many questions that raged among the academic community and the common people. Three conferences that Galilei held almost immediately between November and December in the Aula Magna of the Bo, the central building of the University. A month after Galilei's lectures a treatise on the supernova appeared in Padua. The unknown Antonio Lorenzini, behind whose name it is easy to see the inspiration of Cesare Cremonini, an Aristotelian professor of natural philosophy in Padua, published a booklet entitled Discourse about the new star which debunked the conclusions of Galilei. One month after was published in Padua by the same editor the Dialogo de Cecco di Ronchitti da Bruzene in perpuosito de la stella nuova, a booklet in Paduan dialect replying to Lorenzini. The Dialogo appears in the national edition of Galilei's works and is attributed to Galileo himself with the help of the monk Girolamo Spinelli; it does not appear instead a poem in octaves, by an unknown author (presumably Galilei), published as an appendix to the first edition of 1605, and immediately replaced in the second edition. We publish it here, with a comment.

physics.hist-ph↗

arXiv2022

A Solution to Galileo's Enigma "Mostro Son Io"

Galileo Galilei was a skilled writer and explored several genres, from the well-known scientific writings (often in the form of dialogs) to theater and poetry. His last published poem, "Mostro son io" (A Monster am I), is a riddle written in the form of a sonnet. We suggest that the solution to Galileo's riddle is the Zodiac.

physics.hist-ph↗

arXiv2021

An immersive Open Source environment using Godot

We present a sample implementation of a Virtual and Augmented Reality immersive environment based on Free and Libre Open Source Hardware and Software and the HTC Vive system, used to enhance the immersive experience of the user and to track her/his movements. The sense of immersion has increased and stimulated using a footplate and a Tibetan bridge, connected to the virtual world as Augmented Reality applications and implemented through an Arduino board, thereby adopting a low cost, open source hardware and software approach. The proposed architecture is relatively affordable from the cost point of view, easy to implement, configure and adapt to different contexts. It can be of great help for organizing laboratory classes for young students to afford the implementation of virtual worlds and Augmented Reality applications.

cs.GR↗

arXiv2021

Axion-Like Particle Searches with IACTs

The growing interest in axion-like particles (ALPs) stems from the fact that they provide successful theoretical explanations of physics phenomena, from the anomaly of the CP-symmetry conservation in strong interactions to the observation of an unexpectedly large TeV photon flux from astrophysical sources, at distances where the strong absorption by the intergalactic medium should make the signal very dim. In this latter condition, which is the focus of this review, a possible explanation is that TeV photons convert to ALPs in the presence of strong and/or extended magnetic fields, such as those in the core of galaxy clusters or around compact objects, or even those in the intergalactic space. This mixing affects the observed $γ$-ray spectrum of distant sources, either by signal recovery or the production of irregularities in the spectrum, called "wiggles", according to the specific microscopic realization of the ALP and the ambient magnetic field at the source, and in the Milky Way, where ALPs may be converted back to $γ$ rays. ALPs are also proposed as candidate particles for the Dark Matter. Imaging Atmospheric Cherenkov telescopes (IACTs) have the potential to detect the imprint of ALPs in the TeV spectrum from several classes of sources. In this contribution, we present the ALP case and review the past decade of searches for ALPs with this class of instruments.

astro-ph.HE↗

arXiv2021

Gamma-ray Astrophysics in the MeV Range: the ASTROGAM Concept and Beyond

The energy range between about 100 keV and 1 GeV is of interest for a vast class of astrophysical topics. In particular, (1) it is the missing ingredient for understanding extreme processes in the multi-messenger era; (2) it allows localizing cosmic-ray interactions with background material and radiation in the Universe, and spotting the reprocessing of these particles; (3) last but not least, gamma-ray emission lines trace the formation of elements in the Galaxy and beyond. In addition, studying the still largely unexplored MeV domain of astronomy would provide for a rich observatory science, including the study of compact objects, solar- and Earth-science, as well as fundamental physics. The technological development of silicon microstrip detectors makes it possible now to detect MeV photons in space with high efficiency and low background. During the last decade, a concept of detector ("ASTROGAM") has been proposed to fulfil these goals, based on a silicon hodoscope, a 3D position-sensitive calorimeter, and an anticoincidence detector. In this paper we stress the importance of a medium size (M-class) space mission, dubbed "ASTROMEV", to fulfil these objectives.

astro-ph.IM↗

arXiv2020

Enrico Fermi in Argentina and his Lectures in Buenos Aires, Cordoba and La Plata

In 1934 Enrico Fermi accepted an invitation to deliver lectures in Argentina, Brazil and Uruguay. He arrived in Buenos Aires on July 30, lectured in Buenos Aires, Cordoba, La Plata and Montevideo, and then moved on August 18 to Sao Paulo via Santos and Rio de Janeiro; he traveled back from Rio to Naples on September 1st. His visit had a large resonance, and halls were crowded despite the fact that he lectured in Italian. The University of Buenos Aires recorded his five lectures and transcribed them in Spanish. They contain the first public presentations of the theory of beta decay and of the works on artificial radioactivity started by the via Panisperna group, but are not included in Fermi's Collected Works edited by the Accademia dei Lincei in Rome and by the University of Chicago, although listed in the Bibliography. In this paper we present the transcription of Fermi's five lectures in Buenos Aires, a summary of the lecture in La Plata and an extended summary of the lecture in Cordoba, translating them in English for the first time.

physics.hist-ph↗

arXiv2020

Hint at an axion-like particle from the redshift dependence of blazar spectra

We consider the largest observed sample including all intermediate-frequency peaked (IBL) and high-frequency peaked (HBL) flaring blazars above 100 GeV up to redshift $z = 0.6$. We show that the best-fit regression line of the emitted spectral indices $Γ_{\rm em} (z)$ is a concave parabola decreasing as $z$ increases, thereby implying a statistical correlation between the $\{Γ_{\rm em} (z) \}$ distribution and $z$. This result contradicts our expectation that such a distribution should be $z$-independent. We argue that the above correlation does not arise from any selection bias. We show that our expectation naturally emerges provided that axion-like particles (ALPs) are put into the game. Moreover, ALPs can also explain why flat spectrum radio quasars emit up to 400 GeV, in sharp contradiction with conventional physics. So, the combination of the two very different but consistent results -- taken at face value -- leads to a hint at an ALP with mass $m = {\cal O} (10^{-10} \, {\rm eV})$ and two-photon coupling in the range $2.94 \times 10^{- 12} \, {\rm GeV}^{- 1} < g_{a γγ} < 0.66 \times 10^{- 10} \, {\rm GeV}^{- 1}$. As a bonus, the Universe would become considerably more transparent above energies $E \gtrsim 1 \, {\rm TeV}$ than dictated by conventional physics. Our prediction can be checked not only by the new generation of observatories like CTA, HAWC, GAMMA-400, LHAASO, TAIGA-HiSCORE and HERD, but also thanks to the planned laboratory experiments ALPS II (upgraded), STAX, IAXO and with other techniques now being developed by Avignone and collaborators.

astro-ph.HE↗

arXiv2019

All-sky Medium Energy Gamma-ray Observatory: Exploring the Extreme Multimessenger Universe

The All-sky Medium Energy Gamma-ray Observatory (AMEGO) is a probe class mission concept that will provide essential contributions to multimessenger astrophysics in the late 2020s and beyond. AMEGO combines high sensitivity in the 200 keV to 10 GeV energy range with a wide field of view, good spectral resolution, and polarization sensitivity. Therefore, AMEGO is key in the study of multimessenger astrophysical objects that have unique signatures in the gamma-ray regime, such as neutron star mergers, supernovae, and flaring active galactic nuclei. The order-of-magnitude improvement compared to previous MeV missions also enables discoveries of a wide range of phenomena whose energy output peaks in the relatively unexplored medium-energy gamma-ray band.

astro-ph.IM↗

arXiv2019

Oral History Interview with Marcello Cresti

Marcello Cresti graduated in Physics in 1950 at the University of Pisa by attending the Scuola Normale Superiore; he became professor of Experimental Physics in Padua in 1965, and then Rector of the University of Padua in 1984. His research was focused on the physics of cosmic rays and elementary particles; he started collaborations with research laboratories in Berkeley, Geneva, and with Max-Planck Institutes, which influenced the evolution of research on fundamental physics.

physics.hist-ph↗

arXiv2019

Supermassive black holes at high redshifts

MeV blazars are the most luminous persistent sources in the Universe and emit most of their energy in the MeV band. These objects display very large jet powers and accretion luminosities and are known to host black holes with a mass often exceeding $10^9 M_{\odot}$. An MeV survey, performed by a new generation MeV telescope which will bridge the entire energy and sensitivity gap between the current generation of hard X-ray and gamma-ray instruments, will detect $>$1000 MeV blazars up to a redshift of $z=5-6$. Here we show that this would allow us: 1) to probe the formation and growth mechanisms of supermassive black holes at high redshifts, 2) to pinpoint the location of the emission region in powerful blazars, 3) to determine how accretion and black hole spin interplay to power the jet.

astro-ph.HE↗

arXiv2019

Cosmic Rays and Interstellar Medium with Gamma-Ray Observations at MeV Energies

Latest precise cosmic-ray (CR) measurements and present gamma-ray observations have started challenging our understanding of CR transport and interaction in the Galaxy. Moreover, because the density of CRs is similar to the density of the magnetic field, gas, and starlight in the interstellar medium (ISM), CRs are expected to affect the ISM dynamics, including the physical and chemical processes that determine transport and star formation. In this context, observations of gamma-ray emission at MeV energies produced by the low-energy CRs are very important and urgent. A telescope covering the energy range between ~0.1 MeV and a few GeV with a sensitivity more than an order of magnitude better than previous instruments would allow for the first time to study in detail the low-energy CRs, providing information on their sources, their spectra throughout the Galaxy, their abundances, transport properties, and their role on the evolution of the Galaxy and star formation. Here we discuss the scientific prospects for studies of CRs, ISM (gas, interstellar photons, and magnetic fields) and associated gamma-ray emissions with such an instrument.

astro-ph.HE↗

arXiv2018

Gamma-Ray Astrophysics

High-energy photons are a powerful probe for astrophysics and for fundamental physics in extreme conditions. During the recent years, our knowledge of the most violent phenomena in the Universe has impressively progressed thanks to the advent of new detectors for gamma rays, both at ground and on satellites. This article reviews the present status of high-energy gamma-ray astrophysics, with emphasis on the recent results and a look to the future.

astro-ph.HE↗

arXiv2017

e-ASTROGAM mission: a major step forward for gamma-ray polarimetry

e-ASTROGAM is a gamma-ray space mission proposed for the fifth Medium-size mission (M5) of the European Space Agency. It is dedicated to the study of the non-thermal Universe in the photon energy range from ~0.15 MeV to 3 GeV with unprecedented sensitivity, angular and energy resolution, together with a groundbreaking capability for gamma-ray polarimetric measurements over its entire bandwidth. We discuss here the main polarization results expected at low energies, between 150 keV and 5 MeV, using Compton interactions in the e-ASTROGAM instrument, from observations of active galactic nuclei, gamma-ray bursts, microquasars, and the Crab pulsar and nebula. The anticipated performance of the proposed observatory for polarimetry is illustrated by simulations of the polarization signals expected from various sources. We show that polarimetric analyses with e-ASTROGAM should provide definitive insight into the geometry, magnetization and content of the high-energy plasmas found in the emitting sources, as well as on the processes of radiation of these plasmas.

astro-ph.HE↗

arXiv2017

The e-ASTROGAM mission (exploring the extreme Universe with gamma rays in the MeV-GeV range)

e-ASTROGAM (`enhanced ASTROGAM') is a breakthrough Observatory mission dedicated to the study of the non-thermal Universe in the photon energy range from 0.3 MeV to 3 GeV. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. In the largely unexplored MeV-GeV domain, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on Galactic ecosystems. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous generation instruments, will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LIGO-Virgo-GEO600-KAGRA, SKA, ALMA, E-ELT, TMT, LSST, JWST, Athena, CTA, IceCube, KM3NeT, and the promise of eLISA. Keywords: High-energy gamma-ray astronomy, High-energy astrophysics, Nuclear Astrophysics, Compton and Pair creation telescope, Gamma-ray bursts, Active Galactic Nuclei, Jets, Outflows, Multiwavelength observations of the Universe, Counterparts of gravitational waves, Fermi, Dark Matter, Nucleosynthesis, Early Universe, Supernovae, Cosmic Rays, Cosmic antimatter.

astro-ph.HE↗